Papers
115001
Computational modelling of resistance and associated treatment response heterogeneity in metastatic cancers
Maruša Turk, Urban Simončič, Alison Roth, Damijan Valentinuzzi and Robert Jeraj
View article,Computational modelling of resistance and associated treatment response heterogeneity in metastatic cancersPDF,Computational modelling of resistance and associated treatment response heterogeneity in metastatic cancers
Metastatic cancer patients invariably develop treatment resistance. Different levels of resistance lead to observed heterogeneity in treatment response. The main goal was to evaluate treatment response heterogeneity with a computation model simulating the dynamics of drug-sensitive and drug-resistant cells. Model parameters included proliferation, drug-induced death, transition and proportion of intrinsically resistant cells. The model was benchmarked with imaging metrics extracted from 39 metastatic prostate cancer patients who had 18F-NaF-PET/CT scans performed at baseline and at three cycles into chemotherapy or hormonal therapy. Two initial model assumptions were evaluated: considering only inter-patient heterogeneity and both inter-patient and intra-patient heterogeneity in the proportion of intrinsically resistant cells. The correlation between the median proportion of intrinsically resistant cells and baseline patient-level imaging metrics was assessed with Spearman's rank correlation coefficient. The impact of model parameters on simulated treatment response was evaluated with a sensitivity study. Treatment response after periods of six, nine, and 12 months was predicted with the model. The median predicted range of response for patients treated with both therapies was compared with a Wilcoxon rank sum test. For each patient, the time was calculated when the proportion of disease with a non-favourable response outperformed a favourable response. By taking into account inter-patient and intra-patient heterogeneity in the proportion of intrinsically resistant cells, the model performed significantly better (
) than by taking into account only inter-patient heterogeneity (
). The median proportion of intrinsically resistant cells showed a moderate correlation (ρ = 0.55) with mean patient-level uptake, and a low correlation (ρ = 0.36) with the dispersion of mean metastasis-level uptake in a patient. The sensitivity study showed a strong impact of the proportion of intrinsically resistant cells on model behaviour after three cycles of therapy. The difference in the median range of response (MRR) was not significant between cohorts at any time point (p > 0.15). The median time when the proportion of disease with a non-favourable response outperformed the favourable response was eight months, for both cohorts. The model provides an insight into inter-patient and intra-patient heterogeneity in the evolution of treatment resistance.
115002
Influence of cone beam CT (CBCT) scan parameters on size specific dose estimate (SSDE): a Monte Carlo study
Abdullah Abuhaimed, Colin J Martin and Omer Demirkaya
View article,Influence of cone beam CT (CBCT) scan parameters on size specific dose estimate (SSDE): a Monte Carlo studyPDF,Influence of cone beam CT (CBCT) scan parameters on size specific dose estimate (SSDE): a Monte Carlo study
The CT dose index (CTDIvol) is the dosimetric quantity used for multi-slice CT (MSCT) with beams ⩽4 cm. Conversion factors (f size) based on patient size are applied to CTDIvol to adjust for differences in patient size and derive size-specific dose estimates (SSDE) relating to patient dose. The aim of this study is to: (1) investigate use of a similar technique to provide SSDE values for cone beam CT (CBCT) scans, (2) determine whether factors derived for narrow beam MSCT are suitable for CBCT, and (3) investigate the influence of CBCT parameters on f size values.
Monte Carlo simulations were used to model an on-board imager system integrated into a Varian Truebeam linear accelerator, and to assess doses for imaging. The CTDIvol is unsuitable for CBCT dosimetry, thus the assessments were applied to the modification CTDIIEC, recommended by the international electrotechnical commission (IEC). Conversion factors (f size,CBCT) were derived for CBCT to allow adjustment of values for the absorbed dose in water (AD) averaged over the beam width in the middle of the phantoms. Values of AD were evaluated as for CTDI300 measured with a 30 cm long chamber in centres and peripheries of long water phantoms with diameters of 10–40 cm for head and body protocols. Three beam widths 8, 16, and 24 cm were used with tube potentials ranging from 80–140 kV, for full and partial rotation modes. In order to derive f size,CBCT values, calculated values for AD were normalized with respect to the weighted CTDIIEC assessed in standard CTDI phantoms and free-in-air.
Variations in f size,CBCT with beam width were minimal, 1%–5%, but those with tube potential were greater for 80 kV at small diameters reaching 11%. Acquisition mode affected f size,CBCT values by up to 7%. Best-fit curves were derived from the f size,CBCT values and compared to those reported by AAPM TG–204 for MSCT. Conversion factors estimated from these curves for 120 kV were within ±8% and ±13% of the MSCT values over head and body diameters, respectively, representing the majority of the adult population. Therefore, the use of MSCT factors to convert CTDIIEC for CBCT scans may lead to under/overestimation of doses to patients by 5% and 6%, on average, for the head and body protocols, respectively. Best-fit curves of the results from this study provide values that could be used to convert CTDIIEC for specific water-equivalent diameter (Dw) to a SSDE.
115003
Oblique raster scanning: an ion dose delivery procedure with variable energy layers
Ugo Amaldi
View article,Oblique raster scanning: an ion dose delivery procedure with variable energy layersPDF,Oblique raster scanning: an ion dose delivery procedure with variable energy layers
In ion therapy accelerator complexes the dose is delivered 'actively' by subdividing the target in equal energy layers (EELs), which are scanned by a beam spot visiting in sequence the planned spots, previously defined by the treatment planning system. Synchrotrons-based complexes have three problems: (i) the switching from the energy needed to scan one Equal Energy Layer to the next takes time, an effect that is more relevant for the very short treatment times now often required; (ii) the unavoidable 'ripples' of the quadrupoles and bending magnets currents produce large erratic time variations of the extracted current complicating the dose delivery; (iii) in case of superconducting synchrotrons, it is difficult to rapidly change the magnetic field because of the power dumped in the cold masses. These problems are mitigated in the proposed Qblique Raster Scanning procedure, in which the magnet currents of the beamlines vary in synchrony and a beam spot of continuously varying energy moves at a constant velocity in the beam direction scanning layers that are not perpendicular to it. In this paper it is shown that, even for a 13.5 s irradiation of a 0.5 l target, the B-field rates can be as low as dB/dt = 0.1 T s−1 and that the best procedures to follow 0.5 l moving targets, which combines 3D feedback systems with a five-fold rescanning, can be applied by accelerating in the synchrotron about 1010 carbon ions. ORS can be used in combination with respiratory gating,and is advantageous also for (synchro)cyclotrons-based centres: the variable energy beam can be produced with a slowly rotating absorber and a superconducting energy acceptance beamline/gantry system (with ΔE/E = ±1.5%) can substitute the more expensive beam transport systems which have ten times larger energy acceptance (ΔE/E ⩾ ±15%).
115004
Higher SNR PET image prediction using a deep learning model and MRI image
Chih-Chieh Liu and Jinyi Qi
View article,Higher SNR PET image prediction using a deep learning model and MRI imagePDF,Higher SNR PET image prediction using a deep learning model and MRI image
PET images often suffer poor signal-to-noise ratio (SNR). Our objective is to improve the SNR of PET images using a deep neural network (DNN) model and MRI images without requiring any higher SNR PET images in training. Our proposed DNN model consists of three modified U-Nets (3U-net). The PET training input data and targets were reconstructed using filtered-backprojection (FBP) and maximum likelihood expectation maximization (MLEM), respectively. FBP reconstruction was used because of its computational efficiency so that the trained network not only removes noise, but also accelerates image reconstruction. Digital brain phantoms downloaded from BrainWeb were used to evaluate the proposed method. Poisson noise was added into sinogram data to simulate a 6 min brain PET scan. Attenuation effect was included and corrected before the image reconstruction. Extra Poisson noise was introduced to the training inputs to improve the network denoising capability. Three independent experiments were conducted to examine the reproducibility. A lesion was inserted into testing data to evaluate the impact of mismatched MRI information using the contrast-to-noise ratio (CNR). The negative impact on noise reduction was also studied when miscoregistration between PET and MRI images occurs. Compared with 1U-net trained with only PET images, training with PET/MRI decreased the mean squared error (MSE) by 31.3% and 34.0% for 1U-net and 3U-net, respectively. The MSE reduction is equivalent to an increase in the count level by 2.5 folds and 2.9 folds for 1U-net and 3U-net, respectively. Compared with the MLEM images, the lesion CNR was improved 2.7 folds and 1.4 folds for 1U-net and 3U-net, respectively. The results show that the proposed method could improve the PET SNR without having higher SNR PET images.
115005
The following article is Open access
Synthetic 4D-CT of the thorax for treatment plan adaptation on MR-guided radiotherapy systems
Joshua N Freedman, Hannah E Bainbridge, Simeon Nill, David J Collins, Marc Kachelrieß, Martin O Leach, Fiona McDonald, Uwe Oelfke and Andreas Wetscherek
View article,Synthetic 4D-CT of the thorax for treatment plan adaptation on MR-guided radiotherapy systemsPDF,Synthetic 4D-CT of the thorax for treatment plan adaptation on MR-guided radiotherapy systems
MR-guided radiotherapy treatment planning utilises the high soft-tissue contrast of MRI to reduce uncertainty in delineation of the target and organs at risk. Replacing 4D-CT with MRI-derived synthetic 4D-CT would support treatment plan adaptation on hybrid MR-guided radiotherapy systems for inter- and intrafractional differences in anatomy and respiration, whilst mitigating the risk of CT to MRI registration errors.
Three methods were devised to calculate synthetic 4D and midposition (time-weighted mean position of the respiratory cycle) CT from 4D-T1w and Dixon MRI. The first approach employed intensity-based segmentation of Dixon MRI for bulk-density assignment (sCTD). The second step added spine density information using an atlas of CT and Dixon MRI (sCTDS). The third iteration used a polynomial function relating Hounsfield units and normalised T1w image intensity to account for variable lung density (sCTDSL). Motion information in 4D-T1w MRI was applied to generate synthetic CT in midposition and in twenty respiratory phases. For six lung cancer patients, synthetic 4D-CT was validated against 4D-CT in midposition by comparison of Hounsfield units and dose-volume metrics. Dosimetric differences found by comparing sCTD,DS,DSL and CT were evaluated using a Wilcoxon signed-rank test (p = 0.05).
Compared to sCTD and sCTDS, planning on sCTDSL significantly reduced absolute dosimetric differences in the planning target volume metrics to less than 98 cGy (1.7% of the prescribed dose) on average. When comparing sCTDSL and CT, average radiodensity differences were within 97 Hounsfield units and dosimetric differences were significant only for the planning target volume D99% metric. All methods produced clinically acceptable results for the organs at risk in accordance with the UK SABR consensus guidelines and the LungTech EORTC phase II trial. The overall good agreement between sCTDSL and CT demonstrates the feasibility of employing synthetic 4D-CT for plan adaptation on hybrid MR-guided radiotherapy systems.
115006
Deep feature regression (DFR) for 3D vessel segmentation
Jingliang Zhao, Danni Ai, Yang Yang, Hong Song, Yong Huang, Yongtian Wang and Jian Yang
View article,Deep feature regression (DFR) for 3D vessel segmentationPDF,Deep feature regression (DFR) for 3D vessel segmentation
The structural information of coronary arteries has important clinical value for quantitative diagnosis and treatment of coronary artery disease. In this study, a deep feature regression (DFR) method based on a convolutional regression network (CRN) and a stable point clustering mechanism for 3D vessel segmentation is proposed. First, the vessel model is constructed by a vessel section generator and a series of deviation parameter estimators. The generator provides 2D images for the training and prediction processes, while the estimators calculate pose parameters of an input vessel section. Second, estimators are trained by a series of CRNs, in which deep vessel features are automatically learned from 600 000 sample images. Third, we propose a stable point clustering mechanism that evaluates the reliability of the CRN estimation through iterative regression of vessel parameters. This mechanism eliminates the outliers, thereby increasing tracking robustness. Finally, we present a vessel segmentation algorithm using trained deviation parameter estimators. And, the termination criteria are designed based on both the number of stable points and an intensity constraint. The proposed method is evaluated on a public coronary artery data set. The average overlapping ratio and error are 97.5% and 0.27 mm, respectively. A quantitative test on a public cerebral artery data set demonstrates that the proposed DFR method tracks the vessel centerline with high accuracy, for which the average error is less than 0.33 mm.
115007
A study of inter-crystal scatter in dual-layer offset scintillator arrays for brain-dedicated PET scanners
Mohammadreza Teimoorisichani and Andrew L Goertzen
View article,A study of inter-crystal scatter in dual-layer offset scintillator arrays for brain-dedicated PET scannersPDF,A study of inter-crystal scatter in dual-layer offset scintillator arrays for brain-dedicated PET scanners
A dual-layer offset (DLO) detector enables depth-of-interaction (DOI) through light sharing between two layers of scintillation arrays with a single-ended readout (SER) scheme. However, the SER scheme in DLO detectors may lead to a layer misassignment when inter-crystal scattering occurs. The aim of this work is to study inter-crystal scattering and evaluate the effects of layer misidentifications in DLO detectors on the performance of scanners suitable for a brain-dedicated PET insert. The influence of layer misidentification on the coincidence response functions (CRFs) of 3 different DLO detectors with total/front/back layer thicknesses of 15/6/9 mm, 20/8/12 mm, and 25/7.5/17.5 mm and a crystal width of about 3 mm was studied through Monte Carlo simulations. To overcome layer misidentification, we studied a practical DLO detector design in which each layer can be read out independently through a discrete-layer readout (DLR) scheme where light sharing between the layers is avoided. The CRFs of the mentioned DLO detectors assuming SER and DLR were analyzed. To evaluate the effects of layer misidentification on image quality, images of a Derenzo-like phantom were also reconstructed for all DLO and their equivalent single layer PET scanners. Our analysis showed that layer misassignments due to inter-crystal scatter in DLO detectors mainly has effect on the full-width at tenth maximum of the CRFs. According to the reconstructed images of the phantom, no significant improvements in the quality of the images were seen when SER was replaced with DLR. The results suggest that layer misidentification in DLO detectors does not play an important role in the quality of the PET images.
115008
Biomechanically driven intraoperative spine registration during navigated anterior vertebral body tethering
Hugo Jobidon-Lavergne, Samuel Kadoury, Dejan Knez and Carl-Éric Aubin
View article,Biomechanically driven intraoperative spine registration during navigated anterior vertebral body tetheringPDF,Biomechanically driven intraoperative spine registration during navigated anterior vertebral body tethering
The integration of pre-operative biomechanical planning with intra-operative imaging for navigated corrective spine surgery may improve surgical outcomes, as well as the accuracy and safety of manoeuvres such as pedicle screw insertion and cable tethering, as these steps are performed empirically by the surgeon. However, registration of finite element models (FEMs) of the spine remains challenging due to changes in patient positioning and imaging modalities. The purpose of this study was to develop and validate a new method registering a preoperatively constructed patient-specific FEM aimed to plan and assist anterior vertebral body tethering (AVBT) of scoliotic patients, to intraoperative cone beam computed tomography (CBCT) during navigated AVBT procedures. Prior to surgery, the 3D reconstruction of the patient's spine was obtained using biplanar radiographs, from which a patient-specific FEM was derived. The surgical plan was generated by first simulating the standing to intraoperative decubitus position change, followed by the AVBT correction techniques. Intraoperatively, a CBCT was acquired and an automatic segmentation method generated the 3D model for a series of vertebrae. Following a rigid initialization, a multi-level registration simulation using the FEM and the targeted positions of the corresponding reconstructed vertebrae from the CBCT allows for the refinement of the alignment between modalities. The method was tested with 18 scoliotic cases with a mean thoracic Cobb angle of 47° ± 7° having already undergone AVBT. The translation error of the registered FEM vertebrae to the segmented CBCT spine was 1.4 ± 1.2 mm, while the residual orientation error was 2.7° ± 2.6°, 2.8° ± 2.4° and 2.5° ± 2.8° in the coronal, sagittal, and axial planes, respectively. The average surface-to-surface distance was 1.5 ± 1.2 mm. The proposed method is a first attempt to use a patient-specific biomechanical FEM for navigated AVBT, allowing to optimize surgical strategies and screw placement during surgery.
115009
Optical imaging for the characterization of radioactive carbon and oxygen ion beams
Han Gyu Kang, Seiichi Yamamoto, Sodai Takyu, Fumihiko Nishikido, Akram Mohammadi, Ryo Horita, Shinji Sato and Taiga Yamaya
View article,Optical imaging for the characterization of radioactive carbon and oxygen ion beamsPDF,Optical imaging for the characterization of radioactive carbon and oxygen ion beams
Heavy ion therapy is a promising cancer therapy technique due to the sharper Bragg peak and smaller lateral scattering characteristics of heavy ion beams as compared to a proton therapy. Recently, the potential for radioactive ion beam therapy has been investigated in combination with the OpenPET system to improve the accuracy of in vivo beam range verification. However, the characteristics of the radioactive ion beams have not been investigated thoroughly. Optical imaging has been proposed as a novel high-resolution beam range estimation method for heavy ion beams. In this study, high-resolution luminescence imaging and Cerenkov light imaging were performed for the range estimation of radioactive ion beams such as 11C and 15O in the Heavy Ion Medical Accelerator in Chiba (HIMAC) secondary beam line. A polymethyl methacrylate (PMMA) phantom (10.0 × 10.0 × 9.9 cm3) was irradiated by 11C and 15O ion beams. In order to obtain the in-beam luminescence and off-line beam Cerenkov light images, an optical system was used that consisted of a lens and a cooled CCD camera. The Bragg peaks and stopping positions of the 11C and 15O ion beams could be visualized by using the luminescence and Cerenkov light imaging, respectively. The Bragg peaks showed a good correlation with the peak of the luminescence profile with a positional discrepancy of 1 mm and 0.4 mm for the 11C and 15O ion beams, respectively. In conclusion, optical imaging using luminescence and Cerenkov light could be used for the precise range estimation of radioactive ion beams.
115010
Dosimetric impact of esophagus motion in single fraction spine stereotactic body radiotherapy
Xin Wang, Jinzhong Yang, Zhongxiang Zhao, Dershan Luo, Laurence Court, Yongbin Zhang, David Weksberg, Paul D Brown, Jing Li and Amol J Ghia
View article,Dosimetric impact of esophagus motion in single fraction spine stereotactic body radiotherapyPDF,Dosimetric impact of esophagus motion in single fraction spine stereotactic body radiotherapy
Nine patients with single fraction spinal stereotactic body radiation therapy (SBRT) treatment were identified to assess both the intra fraction and daily esophageal motion and associated dosimetric deviation in spinal SBRT. We performed a chained deformable registration of 4D CT phase images to estimate the intra fraction motion magnitude of the esophagus in a breathing cycle. The intra fraction esophageal motion mostly exhibited in the superior–inferior direction with the total motion magnitude increased from the T1 (0.7 mm) to the T11 vertebra level (6.5 mm). The actual dose received by a moving esophagus was estimated by accumulating dose from each phase of the 4D dataset using deformable image registration. In comparison, dose recalculated on the average CT reflects the dose received by a stationary esophagus. Intra fraction motion was found to reduce the maximum dose received by a small volume of esophagus ⩽2 cm3, with the largest absolute and relative dose difference being −80 cGy and −6.4%, respectively. Its effect on the maximum dose received by 5 cm3 of esophagus can be higher or lower with a large percentage difference, but did not result in substantial absolute dose increase to violate the dose constraint of 11.9 Gy we used for plan evaluation. In addition, there was no correlation between the dosimetric deviation and the intra fraction motion magnitude. These findings suggest that 4D CT simulation is not essential with regards to the esophageal dose. The daily motion of the esophagus and its dosimetric impact was investigated by examining the difference of esophagus delineated on both treatment and planning CT after they were registered using boney target. The day to day difference of esophagus was negligible for all cases in this study.
115011
ADMM-based deep reconstruction for limited-angle CT
Jiaxi Wang, Li Zeng, Chengxiang Wang and Yumeng Guo
View article,ADMM-based deep reconstruction for limited-angle CTPDF,ADMM-based deep reconstruction for limited-angle CT
In the real applications of computed tomography (CT) imaging, the projection data of the scanned objects are usually acquired within a limited-angle range because of the limitation of the scanning condition. Under these circ*mstances, conventional analytical algorithms, such as filtered back-projection (FBP), do not work because the projection data are incomplete. The regularization method has proven to be effective for tomographic reconstruction from under-sampled measurements. To deal with the limited-angle CT reconstruction problem, the regularization method is commonly used, but it is difficult to find a generic regularization term and choose the regularization parameters. Moreover, in some cases, the quality of reconstructed images is less than satisfactory. To solve this problem, we developed an alternating direction method of multipliers (ADMM)-based deep reconstruction (ADMMBDR) algorithm for limited-angle CT. First, we used the ADMM algorithm to decompose a regularization reconstruction model. Then, we utilized a deep convolutional neural network (CNN) to replace a part of the ADMM algorithm to reduce artifacts and avoid the choice of the regularization term and the regularization parameter. Furthermore, we conducted some numerical experiments to evaluate the feasibility and the advantages of the proposed algorithm. The results showed that the proposed algorithm had a better performance than several state-of-the-art algorithms; with respect to structure preservation and artifact reduction.
115012
Observation and modulation of the dissolution of histotripsy-induced bubble clouds with high-frame rate plane wave imaging
Kenneth B Bader, Samuel A Hendley, Gregory J Anthony and Viktor Bollen
View article,Observation and modulation of the dissolution of histotripsy-induced bubble clouds with high-frame rate plane wave imagingPDF,Observation and modulation of the dissolution of histotripsy-induced bubble clouds with high-frame rate plane wave imaging
Focused ultrasound therapies are a noninvasive means to ablate tissue. Histotripsy utilizes short ultrasound pulses with sufficient tension to nucleate bubble clouds that impart lethal strain to the surrounding tissues. Tracking bubble cloud dissolution between the application of histotripsy pulses is critical to ensure treatment efficacy. In this study, plane wave B-mode imaging was employed to monitor bubble cloud motion and grayscale at frame rates up to 11.25 kHz. Minimal changes in the area or position of the bubble clouds were observed 50 ms post excitation. The bubble cloud grayscale was observed to decrease with the square root of time, indicating a diffusion-driven process. These results were qualitatively consistent with an analytic model of gas diffusion during the histotripsy process. Finally, the rate of bubble cloud dissolution was found to be dependent on the output of the imaging pulse, indicating an interaction between the bubble cloud and imaging parameters. Overall, these results highlight the utility of plane wave B-mode imaging for monitoring histotripsy bubble clouds.
115013
Intelligent inverse treatment planning via deep reinforcement learning, a proof-of-principle study in high dose-rate brachytherapy for cervical cancer
Chenyang Shen, Yesenia Gonzalez, Peter Klages, Nan Qin, Hyunuk Jung, Liyuan Chen, Dan Nguyen, Steve B Jiang and Xun Jia
View article,Intelligent inverse treatment planning via deep reinforcement learning, a proof-of-principle study in high dose-rate brachytherapy for cervical cancerPDF,Intelligent inverse treatment planning via deep reinforcement learning, a proof-of-principle study in high dose-rate brachytherapy for cervical cancer
Inverse treatment planning in radiation therapy is formulated as solving optimization problems. The objective function and constraints consist of multiple terms designed for different clinical and practical considerations. Weighting factors of these terms are needed to define the optimization problem. While a treatment planning optimization engine can solve the optimization problem with given weights, adjusting the weights to yield a high-quality plan is typically performed by a human planner. Yet the weight-tuning task is labor intensive, time consuming, and it critically affects the final plan quality. An automatic weight-tuning approach is strongly desired. The procedure of weight adjustment to improve the plan quality is essentially a decision-making problem. Motivated by the tremendous success in deep learning for decision making with human-level intelligence, we propose a novel framework to adjust the weights in a human-like manner. This study used inverse treatment planning in high-dose-rate brachytherapy (HDRBT) for cervical cancer as an example. We developed a weight-tuning policy network (WTPN) that observes dose volume histograms of a plan and outputs an action to adjust organ weighting factors, similar to the behaviors of a human planner. We trained the WTPN via end-to-end deep reinforcement learning. Experience replay was performed with the epsilon greedy algorithm. After training was completed, we applied the trained WTPN to guide treatment planning of five testing patient cases. It was found that the trained WTPN successfully learnt the treatment planning goals and was able to guide the weight tuning process. On average, the quality score of plans generated under the WTPN's guidance was improved by ~8.5% compared to the initial plan with arbitrarily set weights, and by 10.7% compared to the plans generated by human planners. To our knowledge, this was the first time that a tool was developed to adjust organ weights for the treatment planning optimization problem in a human-like fashion based on intelligence learnt from a training process, which was different from existing strategies based on pre-defined rules. The study demonstrated potential feasibility to develop intelligent treatment planning approaches via deep reinforcement learning.
115014
NEMA NU 4-2008 and in vivo imaging performance of RAYCAN trans-PET/CT X5 small animal imaging system
J Teuho, C Han, L Riehakainen, A Honkaniemi, M Tirri, H Liljenbäck, J Virta, S Gu, S Liu, L Wan et al
View article,NEMA NU 4-2008 and in vivo imaging performance of RAYCAN trans-PET/CT X5 small animal imaging systemPDF,NEMA NU 4-2008 and in vivo imaging performance of RAYCAN trans-PET/CT X5 small animal imaging system
The RAYCAN Trans-PET/CT X5 is a preclinical positron emission tomography and computed tomography (PET/CT) system intended for in vivo imaging of rats and mice, featuring all-digital readout electronics for PET data acquisition.
The National Electrical Manufacturers Association (NEMA) NU 4-2008 performance evaluation was conducted on the RAYCAN Trans-PET/CT X5 in addition to assessing in vivo imaging performance of the system on live animals. The performance characteristics of the system were evaluated, including system spatial resolution, count rate performance, sensitivity and image quality. The system imaging performance is assessed in dynamic in vivo PET imaging.
The system resolution defined as full width half maximum (FWHM) was 2.07 mm, 2.11 mm and 1.31 mm for the tangential, radial and axial resolution, respectively, at the center of the field of view. The peak noise equivalent count rate (NECR) values measured were 61 kcps at 0.19 MBq ml−1 for the rat size phantom and 126 kcps at 1.53 MBq ml−1 for the mouse size phantom. Scatter fractions were 24% and 14% for the rat and mouse phantom. The measured peak sensitivity of the system was 1.70%. Image quality in static imaging was deemed sufficient based on the image quality phantom study, with average activity concentration of 155 ± 8.6 kBq ml−1 and image uniformity of 5.57% when using two-dimensional filtered backprojection algorithm (2D-FBP). Rods in the image quality phantom were visualized easily up to 2 mm in size. In dynamic in vivo PET imaging, time-activity-curves from several regions were successfully measured, characterizing the radioactivity distribution in myocardial blood pool, liver, left ventricle and the lung.
In conclusion, the RAYCAN Trans-PET/CT X5 system can be considered a suitable option for basic imaging needs in preclinical imaging.
115015
Energy dependence of a scintillating fiber detector for preclinical dosimetry with an image guided micro-irradiator
C Le Deroff, A-M Frelin and X Ledoux
View article,Energy dependence of a scintillating fiber detector for preclinical dosimetry with an image guided micro-irradiatorPDF,Energy dependence of a scintillating fiber detector for preclinical dosimetry with an image guided micro-irradiator
The dosimetry of preclinical micro-irradiators is challenging due to their millimetric beams and medium x-ray energy range. Plastic scintillator dosimeters (PSD) are good candidates for such a purpose as they provide a high spatial resolution although they show an energy dependence below 100 keV. The purpose of this study was to assess the energy dependence of a dedicated PSD (called DosiRat) for micro-irradiators dosimetry.
The response of the PSD relative to air kerma was measured for different beam qualities (40–225 kV) with the X-RAD 225Cx irradiator. The corresponding energy spectra, determined by Monte Carlo simulations, allowed for correcting the differences in absorbed dose between the DosiRat material (polystyrene) and the air and therefore allowed to compare DosiRat intrinsic energy response to the Birks scintillation quenching model. The energy response of DosiRat was then assessed under preclinical conditions through percentage depth dose curves (PDD) and relative output factor (ROF) measurements in water for beam diameters ranging from 1 to 25 mm.
DosiRat energy response showed a coefficient of variation of 23% from 40 to 225 kV, mainly explained by the mass energy-absorption coefficient variation between polystyrene and air. A remaining variation was shown to be caused by the quenching of the scintillation and was correctly reproduced by the Birks model (with kB = 10.27 mg MeV−1 cm−2). PDD and ROF measurements highlighted an energy response variation with depth and collimation up to 10%. A dose accuracy better than 1% was finally achieved with appropriate calibration and correction factors (CF), for beam collimations larger than the detector (
2 mm diameter).
DosiRat energy dependence was fully characterized in preclinical energy range and shown to be negligible with convenient calibration and corrections factors. It provided accurate dosimetry for medium energy (225 kV) and millimetric beams (down to 2.5 mm).
115016
Data acquisition system for MAET with magnetic field measurements
Keivan Kaboutari, Ahmet Önder Tetik, Elyar Ghalichi, Mehmet Soner Gözü, Reyhan Zengin and Nevzat Güneri Gençer
View article,Data acquisition system for MAET with magnetic field measurementsPDF,Data acquisition system for MAET with magnetic field measurements
Magneto-acousto-electrical tomography (MAET) is an imaging modality to image the electrical conductivity of biological tissues. It is based on electrical current induction by using ultrasound under a static magnetic field. The aim of this study is to develop a data acquisition system for MAET based on magnetic field measurements. The static magnetic field is generated by six permanent neodymium magnets. A 16-element linear phased array (LPA) transducer is utilized to generate acoustic pressure waves inside the phantom. To measure the magnetic field intensity generated by the induced currents, contactless receiver sensors are developed using two similar disk multiple layer coils, which are Helmholtz coil sensor. Physical properties and electrical characteristics of the sensors are assessed. A two-stage cascaded amplifier is designed and utilized in the receiving system. The gain of the cascaded amplifier at 1 MHz is adjusted to be 96 dB. Experimental studies are conducted with two different phantoms, having 3 S m−1 and 58 S m−1 electrical conductivity, respectively. A-scan and B-scan images of phantoms are obtained with the LPA transducer. Comparison of the ultrasound (A-scan) and MAET signals reveals that 3 S m−1 conductive inhom*ogeneity can be detected with this data acquisition system. Furthermore, the front and rear interfaces of an inhom*ogeneity (
) of 58 S m−1 conductivity are detectable.
115017
Development of a deep neural network for generating synthetic dual-energy chest x-ray images with single x-ray exposure
Donghoon Lee, Hwiyoung Kim, Byungwook Choi and Hee-Joung Kim
View article,Development of a deep neural network for generating synthetic dual-energy chest x-ray images with single x-ray exposurePDF,Development of a deep neural network for generating synthetic dual-energy chest x-ray images with single x-ray exposure
Dual-energy chest radiography (DECR) is a medical imaging technology that can improve diagnostic accuracy. This technique can decompose single-energy chest radiography (SECR) images into separate bone- and soft tissue-only images. This can, however, double the radiation exposure to the patient. To address this limitation, we developed an algorithm for the synthesis of DECR from a SECR through deep learning.
To predict high resolution images, we developed a novel deep learning architecture by modifying a conventional U-net to take advantage of the high frequency-dominant information that propagates from the encoding part to the decoding part. In addition, we used the anticorrelated relationship (ACR) of DECR for improving the quality of the predicted images. For training data, 300 pairs of SECR and their corresponding DECR images were used. To test the trained model, 50 DECR images from Yonsei University Severance Hospital and 662 publicly accessible SECRs were used. To evaluate the performance of the proposed method, we compared DECR and predicted images using a structural similarity approach (SSIM). In addition, we quantitatively evaluated image quality calculating the modulation transfer function and coefficient of variation.
The proposed model selectively predicted the bone- and soft tissue-only CR images from an SECR image. The strategy for improving the spatial resolution by ACR was effective. Quantitative evaluation showed that the proposed method with ACR showed relatively high SSIM (over 0.85). In addition, predicted images with the proposed ACR model achieved better image quality measures than those of U-net.
In conclusion, the proposed method can obtain high-quality bone- and soft tissue-only CR images without the need for additional hardware for double x-ray exposures in clinical practice.
115018
Qualitative microwave imaging of breast cancer with contrast agents
Mehmet Nuri Akıncı, Mehmet Çayören and Ersin Göse
View article,Qualitative microwave imaging of breast cancer with contrast agentsPDF,Qualitative microwave imaging of breast cancer with contrast agents
A microwave imaging (MWI) methodology for early diagnosis of breast cancer is presented. Instead of generating a tomographic image of the breast, the proposed technique aims to reconstruct a map of malignant tumours inside the breast by adopting an extended form of factorization method. The implementation of factorization method requires (i) two multi-static scattered field measurements around the breast, which correspond to two different states of the breast, and (ii) the inhom*ogeneous Green's function associated to the breast. For this purpose, the paper proposes the use of contrast agents, which selectively increase the dielectric properties of the malign tissues. Two multi-static field measurements are collected before and after the administration of contrast agents. Later, the inhom*ogeneous Green's function of the breast is estimated by back-propagating the scattered field measurements, which are taken before the contrast agent usage. The feasibility and efficiency of the proposed technique are demonstrated with numerical examples that are performed on a slice of the realistic breast phantoms, which are derived from real three dimensional magnetic resonance imaging (3D-MRI) measurements.
115019
Dual-source photon counting detector CT with a tin filter: a phantom study on iodine quantification performance
Ashley Tao, Richard Huang, Shengzhen Tao, Gregory J Michalak, Cynthia H McCollough and Shuai Leng
View article,Dual-source photon counting detector CT with a tin filter: a phantom study on iodine quantification performancePDF,Dual-source photon counting detector CT with a tin filter: a phantom study on iodine quantification performance
Photon counting detectors (PCD) can provide spectral information to enable iodine quantification through multi-energy imaging but performance is limited by current PCD technology. The purpose of this work is to evaluate iodine quantification in a phantom study using dual-source PCD-CT (DS-PCD-CT), and compare to single-source (SS)-PCD-CT and traditional DS energy integrating detector (EID)-based dual-energy CT.
A multi-energy CT phantom with iodine inserts (0 to 15 mg ml−1 concentration) was imaged on a research SS-PCD-CT scanner (CTDIvol = 18 mGy). A DS-PCD-CT was emulated by acquiring two sequential scans (CTDIvol = 9 mGy each) using tube potentials: 140 kVp/80 kVp, 140 kVp/100 kVp and 140 kVp/120 kVp. For each kVp, 1 or 2 energy bins were reconstructed to achieve either dual-energy or quadruple energy CT. In addition to these energy combinations, a Sn filter was used for the high tube potential (140 kVp) of each kVp pair. For comparison, the same phantom was also scanned on a commercially available DS-EID-CT with matched radiation dose (CTDIvol = 18 mGy). Material decomposition was performed in image space using a standard least-squares based approach to generate iodine and water-specific images. The root-mean-square-error (RMSE) measured over each insert from the iodine image was used to determine iodine accuracy.
The iodine RMSE from SS-PCD (140 kVp with 2 energy bins) was 2.72 mg ml−1. The use of a DS configuration with 1 energy bin per kVp (140 kVp/80 kVp) resulted in a RMSE of 2.29 mg ml−1. Two energy bins per kVp further reduced iodine RMSE to 1.83 mg ml−1. The addition of a Sn filter to the latter quadruple energy mode reduced RMSE to 1.48 mg ml−1. RMSE for DS-PCD-CT (2 energy bins per kVp) decreased by 1.3% (Sn140 kVp/80 kVp) and 15% (Sn140 kVp/100 kVp) as compared to DS-EID-CT.
DS-PCD-CT with a Sn filter improved iodine quantification as compared to both SS-PCD-CT and DS-EID-CT.
115020
The potential of photon-counting CT for quantitative contrast-enhanced imaging in radiotherapy
Mikaël Simard, Andréanne Lapointe, Arthur Lalonde, Houda Bahig and Hugo Bouchard
View article,The potential of photon-counting CT for quantitative contrast-enhanced imaging in radiotherapyPDF,The potential of photon-counting CT for quantitative contrast-enhanced imaging in radiotherapy
The aim of this study is to use a simulation environment to evaluate the potential of using photon-counting CT (PCCT) against dual-energy CT (DECT) in the context of quantitative contrast-enhanced CT for radiotherapy. An adaptation of Bayesian eigentissue decomposition by Lalonde et al (2017 Med. Phys. 44 5293–302) that incorporates the estimation of contrast agent fractions and virtual non-contrast (VNC) parameters is proposed, and its performance is validated against conventional maximum likelihood material decomposition methods for single and multiple contrast agents. PCCT and DECT are compared using two simulation frameworks: one including ideal CT numbers with image-based Gaussian noise and another defined as a virtual patient with projection-based Poisson noise and beam hardening artifacts, with both scenarios considering spectral distortion for PCCT. The modalities are compared for their accuracy in estimating four key physical parameters: (1) the contrast agent fraction, as well as VNC parameters relevant to radiotherapy such as the (2) electron density, (3) proton stopping power and (4) photon linear attenuation coefficient. Considering both simulation frameworks, a reduction of root mean square (RMS) errors with PCCT is noted for all physical parameters evaluated, with the exception of the error on the contrast agent fraction being about constant through modalities in the virtual patient. Notably, for the virtual patient, RMS errors on VNC electron density and stopping power are respectively reduced from 2.0% to 1.4% and 2.7% to 1.4% when going from DECT to PCCT with four energy bins. The increase in accuracy is comparable to the differences between contrast-enhanced and non-contrast DECT. This study suggests that in a realistic simulation environment, the overall accuracy of radiotherapy-related parameters can be increased when using PCCT with four energy bins instead of DECT. This confirms the potential of PCCT to provide robust and quantitative tissue parameters for contrast-enhanced CT required in radiotherapy applications.
115021
Microwave thermal ablation using CT-scanner for predicting the variation of ablated region over time: advantages and limitations
L Strigari, S Minosse, D D'Alessio, L Farina, M Cavagnaro, B Cassano, R Pinto, G Vallati and V Lopresto
View article,Microwave thermal ablation using CT-scanner for predicting the variation of ablated region over time: advantages and limitationsPDF,Microwave thermal ablation using CT-scanner for predicting the variation of ablated region over time: advantages and limitations
This study aims at investigating in real-time the structural and dynamical changes occurring in an ex vivo tissue during a microwave thermal ablation (MTA) procedure. The experimental set-up was based on ex vivo liver tissue inserted in a dedicated box, in which 3 fibre-optic (FO) temperature probes were introduced to measure the temperature increase over time. Computed tomography (CT) imaging technique was exploited to experimentally study in real-time the Hounsfield Units (HU) modification occurring during MTA. The collected image data were processed with a dedicated MATLAB tool, developed to analyse the FO positions and HU modifications from the CT images acquired over time before and during the ablation procedures. The radial position of a FO temperature probe (rFO) and the value of HU in the region of interest (ROI) containing the probe (HUo), along with the corresponding value of HU in the contralateral ROI with respect to the MTA antenna applicator (HUc), were determined and registered over time during and after the MTA procedure. Six experiments were conducted to confirm results. The correlation between temperature and the above listed predictors was investigated using univariate and multivariate analysis. At the multivariate analysis, the time, rFO and HUc resulted significant predictive factors of the logarithm of measured temperature. The correlation between predicted and measured temperatures was 0.934 (p < 0.001). The developed tool allows identifying and registering the image-based parameters useful for predicting the temperature variation over time in each investigated voxel by taking into consideration the HU variation.
115022
Ultrasound multiple scattering with microbubbles can differentiate between tumor and healthy tissue in vivo
Kaustav Mohanty, Virginie Papadopoulou, Isabel G Newsome, Sarah Shelton, Paul A Dayton and Marie Muller
View article,Ultrasound multiple scattering with microbubbles can differentiate between tumor and healthy tissue in vivoPDF,Ultrasound multiple scattering with microbubbles can differentiate between tumor and healthy tissue in vivo
Most solid tumors are characterized by highly dense, isotropic vessel networks. Characterization of such features has shown promise for early cancer diagnosis. Ultrasound diffusion has been used to characterize the micro-architecture of complex media, such as bone and the lungs. In this work, we examine a non-invasive diffusion-based ultrasound technique to assess neo-vascularization. Because the diffusion constant reflects the density of scatterers in heterogeneous media, we hypothesize that by injecting microbubbles into the vasculature, ultrasound diffusivity can reflect vascular density (VD), thus differentiating the microvascular patterns between tumors and healthy tissue. The diffusion constant and its anisotropy are shown to be significantly different between fibrosarcoma tumors (n = 16) and control tissue (n = 18) in a rat animal model in vivo. The diffusion constant values for control and tumor were found to be 1.38 ± 0.51 mm2µs−1 and 0.65 ± 0.27 mm2µs−1, respectively. These results are corroborated with VD from acoustic angiography (AA) data, confirming increased vessel density in tumors compared to controls. The diffusion constant offers a promising way to quantitatively assess vascular networks when combined with contrast agents, which may allow early tumor detection and characterization.
115023
Deformable image registration for dose mapping between external beam radiotherapy and brachytherapy images of cervical cancer
B Rigaud, A Klopp, S Vedam, A Venkatesan, N Taku, A Simon, P Haigron, R de Crevoisier, K K Brock and G Cazoulat
View article,Deformable image registration for dose mapping between external beam radiotherapy and brachytherapy images of cervical cancerPDF,Deformable image registration for dose mapping between external beam radiotherapy and brachytherapy images of cervical cancer
For locally advanced cervical cancer (LACC), anatomy correspondence with and without BT applicator needs to be quantified to merge the delivered doses of external beam radiation therapy (EBRT) and brachytherapy (BT). This study proposed and evaluated different deformable image registration (DIR) methods for this application.
Twenty patients who underwent EBRT and BT for LACC were retrospectively analyzed. Each patient had a pre-BT CT at EBRT boost (without applicator) and a CT and MRI at BT (with applicator). The evaluated DIR methods were the diffeomorphic Demons, commercial intensity and hybrid methods, and three different biomechanical models. The biomechanical models considered different boundary conditions (BCs). The impact of the BT devices insertion on the anatomy was quantified. DIR method performances were quantified using geometric criteria between the original and deformed contours. The BT dose was deformed toward the pre-CT BT by each DIR method. The impact of boundary conditions to drive the biomechanical model was evaluated based on the deformation vector field and dose differences. The GEC-ESTRO guideline dose indices were reported.
Large organ displacements, deformations, and volume variations were observed between the pre-BT and BT anatomies. Rigid registration and intensity-based DIR resulted in poor geometric accuracy with mean Dice similarity coefficient (DSC) inferior to 0.57, 0.63, 0.42, 0.32, and 0.43 for the rectum, bladder, vagin*, cervix and uterus, respectively. Biomechanical models provided a mean DSC of 0.96 for all the organs. By considering the cervix-uterus as one single structure, biomechanical models provided a mean DSC of 0.88 and 0.94 for the cervix and uterus, respectively. The deformed doses were represented for each DIR method.
Caution should be used when performing DIR for this application as standard techniques may have unacceptable results. The biomechanical model with the cervix-uterus as one structure provided the most realistic deformations to propagate the BT dose toward the EBRT boost anatomy.
115024
Experimental validation of magnetically focused proton beams for radiosurgery
Grant A McAuley, Anthony V Teran, Patrick Q McGee, Theodore T Nguyen, James M Slater, Jerry D Slater and Andrew J Wroe
View article,Experimental validation of magnetically focused proton beams for radiosurgeryPDF,Experimental validation of magnetically focused proton beams for radiosurgery
We performed experiments using a triplet of quadrupole permanent magnets to focus protons and compared their dose distributions with unfocused collimated beams using energies and field sizes typically employed in proton radiosurgery. Experiments were performed in a clinical treatment room wherein small-diameter proton beams were focused by a magnet triplet placed immediately upstream of a water tank. The magnets consisted of segments of Sm2Co17 rare-earth permanent magnetic material adhered into Halbach cylinders with nominal field gradients of 100, 150, 200, and 250 T m−1. Unmodulated beams with initial diameters of 3 mm–20 mm were delivered using a single scattering system with nominal energies of 127 and 157 MeV (respective ranges of ~10 cm and 15 cm in water), commonly used for proton radiosurgery at our institution. For comparison, small-diameter unfocused collimated beams were similarly delivered. Transverse and depth dose distributions were measured using radiochromic film and a diode detector, respectively, and compared between the focused and unfocused beams (UNF). The focused beams produced low-eccentricity beam spots (defined by the 80% dose contour) at Bragg depth, with full width at 80% maximum dose values ranging from 3.8 to 7.6 mm. When initial focused beam diameters were larger than matching unfocused diameters (19 of 29 cases), the focused beams peak-to-entrance dose ratios were 13% to 73% larger than UNF. In addition, in 17 of these cases the efficiency of dose delivery to the target was 1.3× to 3.3× larger. Both peak-to-entrance dose ratios and efficiency tended to increase with initial beam diameter, while efficiency also tended to increase with magnet gradient. These experimental results are consistent with our previous Monte Carlo (MC) studies and suggest that a triplet of quadrupole Halbach cylinders could be clinically useful for irradiating small-field radiosurgical targets with fewer beams, lower entrance dose, and shorter treatment times.
115025
The following article is Open access
Hydrogels as a water bolus during hyperthermia treatment
Hana Dobšíček Trefná and Anna Ström
View article,Hydrogels as a water bolus during hyperthermia treatmentPDF,Hydrogels as a water bolus during hyperthermia treatment
The feasibility of using hydrogels as a water bolus during hyperthermia treatment was assessed. Three types of gels, high methoxyl (HM) pectin/alginate, xanthan/locust bean gum (LBG) and xanthan/LBG/agarose were evaluated based on their dielectric, rheological and mechanical properties. The most suitable, xanthan/LBG/agarose gel was further used as a water bolus in a hyperthermia array applicator. The gels composed of polysaccharides carrying low charge displayed dielectric properties close to those of water, while the dielectric properties of HM pectin/alginate gel was deemed unsuitable for the current application. The mechanical examination shows that the xanthan/LBG gel has a non-brittle behaviour at room temperature, in contrast to the agarose gel. The moduli of the xanthan/LBG gel weaken however considerably between the temperature range of 40 °C and 50 °C, reducing its potential to be used as water bolus. The ternary system of xanthan/LBG/agarose had advantageous behaviour as it was dominated by the thermal hysteresis typical of agarose upon temperature increase, but governed by the typical non-brittle behaviour of the xanthan/LBG at low temperatures. The final evaluation within the hyperthermia applicator showed excellent signal transmission from the antennas. The agarose/xanthan/LBG gel reduced the scattering of electromagnetic waves, enabled a tight closure between the body and the antennas, and offered a less bulky solution than the currently used water-filled plastic bags. The results presented here open up a new application area for hydrogels in improving heat delivery during hyperthermia treatment and other near-field microwave applications.
115026
Non-invasive myocardial performance mapping using 3D echocardiographic stress–strain loops
João Pedrosa, Jürgen duch*enne, Sandro Queirós, Ganna Degtiarova, Olivier Gheysens, Piet Claus, Jens-Uwe Voigt and Jan D'hooge
View article,Non-invasive myocardial performance mapping using 3D echocardiographic stress–strain loopsPDF,Non-invasive myocardial performance mapping using 3D echocardiographic stress–strain loops
Regional contribution to left ventricular (LV) ejection is of much clinical importance but its assessment is notably challenging. While deformation imaging is often used, this does not take into account loading conditions. Recently, a method for intraventricular pressure estimation was proposed, thus allowing for loading conditions to be taken into account in a non-invasive way. In this work, a method for 3D automatic myocardial performance mapping in echocardiography is proposed by performing 3D myocardial segmentation and tracking, thus giving access to local geometry and strain. This is then used to assess local LV stress–strain relationships which can be seen as a measure of local myocardial work. The proposed method was validated against 18F-fluorodeoxyglucose positron emission tomography, the reference method to clinically assess local metabolism. Averaged over all patients, the mean correlation between FDG-PET and the proposed method was 
. In conclusion, stress–strain loops were, for the first time, estimated from 3D echocardiography and correlated to the clinical gold standard for local metabolism, showing the future potential of real-time 3D echocardiography (RT3DE) for the assessment of local metabolic activity of the heart.
115027
Applying a variable relative biological effectiveness (RBE) might affect the analysis of clinical trials comparing photon and proton therapy for prostate cancer
Maria Marteinsdottir and Harald Paganetti
View article,Applying a variable relative biological effectiveness (RBE) might affect the analysis of clinical trials comparing photon and proton therapy for prostate cancerPDF,Applying a variable relative biological effectiveness (RBE) might affect the analysis of clinical trials comparing photon and proton therapy for prostate cancer
The purpose of this study was the evaluation of the impact of a variable relative biological effectiveness (RBE) compared to a constant RBE value of 1.1 in proton therapy prostate trials due to uncertainties in α/β ratio.
Twenty patients receiving passive scattered proton therapy (PSPT) and fifteen patients receiving intensity modulated proton therapy (IMPT) were compared to twenty patients treated with 7-field intensity modulated photon therapy (IMRT). For proton beam therapy (PBT), the RBE was estimated using two different RBE models. Tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP) were assessed.
For one of the RBE models, dosimetric indices assuming a low α/β were ~10%–11% larger compared to using a fixed RBE. A different model resulted in 1%–3% lower values independent of α/β. Comparing PBT with IMRT revealed a negligible difference in TCP for a fixed RBE. Applying a variable RBE revealed an increase in TCP by 6% for PBT compared to IMRT for one model but a decrease of 2% for the other. Variable RBE values in PSPT resulted in an increase in NTCP for rectum from 7% to 11% for a fixed RBE with one model but a decrease to 6% for another. For IMPT, NTCP increased from 5% to 9% for a fixed RBE for one model but decreased to 3% using the other. The NTCP for bladder increased for PSPT for both models, from 11% to 19% and 14%, respectively. For IMPT, the NTCP increased from 12% to 17% using one model but decreased to 11% with the other.
In radiation therapy for prostate cancer, disregarding variable RBE may lead to either underestimation or overestimation of the expected TCP and NTCP, depending on the RBE model and α/β. This should be considered when estimating uncertainties when comparing PBT and IMRT outcomes in clinical trials.
115028
Sentinel lymph node fingerprinting
Uri Nahum, Carlo Seppi, Peter A von Niederhäusern, Simon Pezold, Stephan K Haerle and Philippe C Cattin
View article,Sentinel lymph node fingerprintingPDF,Sentinel lymph node fingerprinting
Background. When locating the sentinel lymph node (SLN), surgeons use state-of-the-art imaging devices, such as a 1D gamma probe or less widely spread a 2D gamma camera. These devices project the 3D subspace onto a 1D respectively 2D space, hence loosing accuracy and the depth of the SLN which is very important, especially in the head and neck area with many critical structures in close vicinity. Recent methods which use a multi-pinhole collimator and a single gamma detector image try to gain a depth estimation of the SLN. The low intensity of the sources together with the computational cost of the optimization process make the reconstruction in real-time, however, very challenging.
Results. In this paper, we use an optimal design approach to improve the classical pinhole design, resulting in a non-symmetric distribution of the pinholes of the collimator. This new design shows a great improvement of the accuracy when reconstructing the position and depth of the radioactive tracer. Then, we introduce our Sentinel lymph node fingerprinting (SLNF) algorithm, inspired by MR-fingerprinting, for fast and accurate reconstruction of the tracer distribution in 3D space using a single gamma detector image. As a further advantage, the method requires no pre-processing, i.e. filtering of the detector image. The method is very stable in its performance even for low exposure times. In our ex vivo experiments, we successfully located multiple Technetium 99m (Tc-99m) sources with an exposure time of only one second and still, with a very small L2-error.
Conclusion. These promising results under short exposure time are very encouraging for SLN biopsy. Although, this device has not been tested on patients yet, we believe: that this approach will give the surgeon accurate 3D positions of the SLN and hence, can potentially reduce the trauma for the patient.
115029
The following article is Open access
Monte Carlo simulations of out-of-field surface doses due to the electron streaming effect in orthogonal magnetic fields
Victor N Malkov, Sara L Hackett, Jochem W H Wolthaus, Bas W Raaymakers and Bram van Asselen
View article,Monte Carlo simulations of out-of-field surface doses due to the electron streaming effect in orthogonal magnetic fieldsPDF,Monte Carlo simulations of out-of-field surface doses due to the electron streaming effect in orthogonal magnetic fields
The out-of-field surface dose contribution due to backscattered or ejected electrons, focused by the magnetic field, is evaluated in this work. This electron streaming effect (ESE) can contribute to out-of-field skin doses in orthogonal magnetic resonance guided radiation therapy machines.
Using the EGSnrc Monte Carlo package, a phantom is set-up along the central axis of an incident 10 
10 cm2 7 MV FFF photon beam. The phantom exit or entry surface is inclined with respect to the magnetic field, and an out-of-field water panel is positioned 10 cm away from, and centered on, the isocenter. The doses from streaming backscattered or ejected electrons, for either a 0.35 T or 1.5 T magnetic field, are evaluated in the out-of-field water panel for surface inclines of 10, 30, and 45°.
The magnetic field focuses electrons emitted from the inclined phantom. Dose distributions at the surface of the out-of-field water panel are sharper in the 1.5 T magnetic field as compared to 0.35 T. The maximum doses for the 0.35 T simulations are 23.2%, 37.8%, and 39.0% for the respective 10, 30, and 45° simulations. For 1.5 T, for the same angles, the maximum values are 17.1%, 29.8%, and 35.8%. Dose values drop to below 2% within the first 1 cm of the out-of-field water phantom. The phantom thickness is an important variable in the magnitude of the ESE dose.
The ESE can produce large out-of-field skin doses and must be a consideration in treatment planning in the MRgRT work-flow. Treatments often include multiple beams which will serve to spread out the effect, and many beams, such as anterior–posterior, will reduce the skin dose due to the ESE. A 1 cm thick shielding of either a bolus placed on the patient or mounted on the present RF coils would greatly reduce the ESE dose contributions. Further exploration of the capabilities of treatment planning systems to screen for this effect is required.
Note
11NT01
Small field correction factors determination for several active detectors using a Monte Carlo method in the Elekta Axesse linac equipped with circular cones
Andrea Girardi, Christian Fiandra, Francesca Romana Giglioli, Elena Gallio, Omar Hammad Ali and Riccardo Ragona
View article,Small field correction factors determination for several active detectors using a Monte Carlo method in the Elekta Axesse linac equipped with circular conesPDF,Small field correction factors determination for several active detectors using a Monte Carlo method in the Elekta Axesse linac equipped with circular cones
A Monte Carlo (MC) method was used to determine small field output correction factors for several active detectors (Exradin A16, Exradin A26, PTW microLion, PTW microDiamond, Exradin W1 and IBA RAZOR) for an Elekta Axesse linac equipped with circular cones. MC model of the linac was built with the GamBet software, using the Penelope code system. The dose-to-water simulation for each cone, ranging from 5 to 30 mm of diameter size, was used to calculate field factors and the results were validated together with Gafchromic EBT3 film. Output factors (OFs) were measured with the active detectors and correction factors were determined using the MC results. The MC simulations agreed with films within 1.2%. OFs measured with Exradin W1 scintillator were in agreement within 0.8% with MC simulations. The Exradin A16 and A26 microchambers under-responded for small fields relative to the MC (−13.1% and −4.6%, respectively). PTW microLion, IBA RAZOR and PTW microDiamond overestimated the output factor for the smallest field (+3.9%, +5.4 and +7.1%, respectively). The present study pointed out that it is crucial to apply the appropriate correction factors in order to provide accurate measurements in small beams geometry. The results showed that the Exradin W1 can be used for very small field dosimetry without correction factors, which shall be contrariwise employed for other detectors.
