bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐J‐158: Experimental Investigation of Proton Radiography Based On Time‐Resolved Dose Measurements
Authors: Testa M , Doolan P , H Bentefour E , Paganetti H , Lu H‐M 
Published: July 2014

Purpose:To use proton radiography for i) in‐vivo range verification of the brain fields of medulloblastoma patients in order to reduce the exit dose to the cranial skin and thus the risk of permanent alopecia; ii) for performing patient specific optimization of the calibration from CT‐Hounsfield units to proton relative stopping power in order to minimize uncertainties of proton rangMethods:We developed and tested a prototype proton radiography system based on a single‐plane scintillation screen coupled with a fast CCD camera (1ms sampling rate, 0.29×0.29 mm2 pixel size, 30×30 cm2 field of view). The method is based on the principle that, for passively scattered beams, the radiological depth of any point in the plateau of a spread‐out Bragg‐Peak (SOBP) can be inferred from the time‐pattern of the dose rate measurements. We performed detector characterization measurements using complex‐shape homogeneous phantoms and an Alderson phantoResults:Detector characterization tests confirmed the robustness of the technique. The results of the phantom measurements are encouraging in terms of achievable accuracy of the water equivalent thickness. A technique to minimize the degradation of spatial resolution due to multiple Coulomb scattering is discussed. Our novel radiographic technique is rapid (100 ms) and simultaneous over the whole field. The dose required to produce one radiograph, with the current settings, is ∼3 cGConclusion:The results obtained with this simple and innovative radiography method are promising and motivate further development of technique. The system requires only a single‐plane 2D dosimeter and it uses the clinical beam for a fraction of second with low dose to the patient
SU‐E‐J‐159: Intra‐Patient Deformable Image Registration Uncertainties Quantified Using the Distance Discordance Metric
Authors: Saleh Z , Thor M , Apte A , Sharp G , Muren L , Deasy J 
Published: July 2014

Purpose:The quantitative evaluation of deformable image registration (DIR) is currently challenging due to lack of a ground truth. In this study we test a new method proposed for quantifying multiple‐image based DIRrelated uncertainties, for DIR of pelvic images.Methods:19 patients were analyzed, each with 6 CT scans, who previously had radiotherapy for prostate cancer. Manually delineated structures for rectum and bladder, which served as ground truth structures, were delineated on the planning CT and each subsequent scan. For each patient, voxel‐by‐voxel DIR‐related uncertainties were evaluated, following B‐spline based DIR, by applying a previously developed metric, the distance discordance metric (DDM; Saleh et al., PMB (2014) 59:733). The DDM map was superimposed on the first acquired CT scan and DDM statistics were assessed, also relative to two metrics estimating the agreement between the propagated and the manually delineated structures.Results:The highest DDM values which correspond to greatest spatial uncertainties were observed near the body surface and in the bowel due to the presence of gas. The mean rectal and bladder DDM values ranged from 1.1–11.1 mm and 1.5–12.7 mm, respectively. There was a strong correlation in the DDMs between the rectum and bladder (Pearson R = 0.68 for the max DDM). For both structures, DDM was correlated with the ratio between the DIR‐propagated and manually delineated volumes (R = 0.74 for the max rectal DDM). The maximum rectal DDM was negatively correlated with the Dice Similarity Coefficient between the propagated and the manually delineated volumes (R= −0.52).Conclusion:The multipleimage based DDM map quantified considerable DIR variability across different structures and among patients. Besides using the DDM for quantifying DIR‐related uncertainties it could potentially be used to adjust for uncertainties in DIR‐based accumulated dose distributions.
SU‐E‐J‐163: Suppressing Motion Related Artifacts in 4D‐CT Or 4D‐CBCT Reconstruction Using Projections and Digitally Reconstructed Projections: Proof of Principle
Authors: Yi B , Lasio G , Liu Y , Yu C , Mistry N 
Published: July 2014

Purpose:It has been always challenging to reconstruct good quality 4D‐CT or 4D‐CBCT when the data are under‐sampled for each individual phase. For example, CBCT data is often acquired with limited number of projections and while it is sufficient to reconstruct decent motion averaged images; reconstructing a 4D image from this limited data leads to motion induced artifacts. However, inherent in the projection data are both components that capture the moving and non‐moving parts of the image. In this work, we test the feasibility of using such a dataset to separate out the moving and non‐moving components and then reconstruct individual phase images to acquire a complete 4D reconstruction with reduced artifacts.Methods:To test our theory, we simulated a simple 2D+time respiratory phantom, and demonstrated the feasibility using a simple filtered backprojection algorithm along with the proposed motion suppression technique to reconstruct 2D+time images. However, the concepts can be expanded to 3D+time (i.e. 4D) datasets both using conventional CT or CBCT acquisition. The core of the technique rests on separating out the motion components from individual projection data by selecting the minimum intensity between projections and digitally reconstructed projections. This information is then later added back into the final images reconstructed at each individual phase to suppress motion artifacts.Results:Initial results on a 2D+time simulated phantom proves that severe under‐sampling artifacts can be eliminated and individual phase images can be reconstructed with high fidelity when compared to standard under‐sampled filtered backprojection.Conclusion:The technique is successfully demonstrated using simple backprojection, and hence computational complexity is comparable to standard backprojection (for CT) or FDK (for CBCT). Computational complexity will be significantly better when compared to traditional iterative methods that use regularization and penalty functions.NIH R01CA133539
SU‐E‐J‐164: An Investigation of a Low‐Cost ‘dry’ Optical‐CT Scanning System for 3D Dosimetry
Authors: Bache S , Malcolm J , Adamovics J , Oldham M 
Published: July 2014

Purpose:To characterize and explore the efficacy of a novel low‐cost, lowfluid, broad‐beam optical‐CT system for 3D‐dosimetry in radiochromic Presage dosimeters. Leading current optical‐CT systems incorporate expensive glass‐based telecentric lens technology, and a fluid bath with substantial amounts of fluid (which introduces an inconvenience factor) to minimize refraction artifacts. Here we introduce a novel system which addresses both these limitations by: (1) the use of Fresnel lenses in a telecentric arrangement, and (2) a ‘solid’ fluid bath which dramatically reduces the amount of fluid required for refractive‐index (RI) matching. MaterialsMethods:A fresnel based telecentric optical‐CT system was constructed which expands light from a single red LED source into a nominally parallel beam into which a cubic ‘dry‐tank’ is placed. The drytank consists of a solid polyurethane cube (with the same RI as Presage) but containing a cylindrical cavity (11.5cm diameter × 11cm) into which the dosimeter is placed for imaging. A narrow (1‐3mm) gap between the walls of the dosimeter and dry‐tank is filled with a fluid of similar RI. This arrangement reduces the amount of RI fluid from about 1000cc to 75cc, yielding substantial practical benefit in convenience and cost. The new system was evaluated in direct comparison against Eclipse planning system from a 4‐field parallel‐opposed treatmenResults:Gamma calculations of dose from DFOS‐dry system versus Eclipse showed 92% and 97% agreement with 4mm/4% and 5mm/5% criteria, respectively, in the central 80% of dose distribution. Reconstructions showed some edge artifacts, as well as some dose underestimation towards the dosimeter edge.Conclusion:The implementation of Fresnel based ‘dry’ optical‐CT for 3Ddosimetry would represent an important advance enhancing costeffectiveness and practical viability. The performance of the prototype presented here is not yet comparable to the state‐of‐the‐art, but shows sufficient promise for further investigation to elevate image quality to match gold‐standard optical‐CT systems.This work was supported by NIH R01CA100835
SU‐E‐J‐165: Ghost Marker Prediction, Detection and Elimination in Marker‐Based Optical Tracking Systems
Authors: Yan G , Li J , Mittauer K , Huang Y , Lu B , Liu C 
Published: July 2014

Purpose:In optical tracking system (OTS), ghost marker (GM) limits users' flexibility in marker placement and can lead to incorrect patient setup or system execution failure. This work aims to model the phenomenon of GM and propose robust algorithms for GM prediction, detection and elimination.Methods:Two GMs occur when two markers and two sensors of the OTS are coplanar. However, when one marker gradually moves out of the plane and breaks the coplanar condition, both GMs briefly remain before they completely disappear. To explain this effect, we expanded line‐line intersection definition and the coplanar condition: two lines intersect when their distance is less than threshold Ω and involved points are said to be coplanar within Ω. We fixed one marker and moved the other through the plane with a 0.1 mm step length. Sensor positions were calculated using a back projection method when coplanar condition was strictly satisfied. Ω was determined as line‐line distance when ghost marker first appeared. The prediction algorithm checks whether any two given markers are coplanar with the two sensors within Ω; the detection algorithm checks whether any marker is near the intersection of lines connecting sensors and two other markers. A backtracking pattern matching algorithm matches markers to reference markers and eliminates unmatched ones as GMs. The algorithms were validated with two phantoms and 40 SBRT patients using 5~8 markers.Results:The prediction success rates were 97.7% and 89.6% and the detection success rates were 100% on the two phantoms (1544 ' 2045 samples). The matching success rates were 100% on both phantoms and patients.Conclusion:The proposed model precisely explains the phenomenon of GMs in marker‐based OTS. The proposed detection and matching algorithms guarantee complete elimination of GMs, thus avoiding errors in SBRT tracking and providing user maximum flexibility in marker placement.
SU‐E‐J‐168: Automated Pancreas Segmentation Based On Dynamic MRI
Authors: Gou S , Rapacchi S , Hu P , Sheng K 
Published: July 2014

Purpose:MRI guided radiotherapy is particularly attractive for abdominal targets with low CT contrast. To fully utilize this modality for pancreas tracking, automated segmentation tools are needed. A hybrid gradient, region growth and shape constraint (hGReS) method to segment 2D upper abdominal dynamic MRI is developed for this purpose.Methods:2D coronal dynamic MR images of 2 healthy volunteers were acquired with a frame rate of 5 f/second. The regions of interest (ROIs) included the liver, pancreas and stomach. The first frame was used as the source where the centers of the ROIs were annotated. These center locations were propagated to the next dynamic MRI frame. 4‐neighborhood region transfer growth was performed from these initial seeds for rough segmentation. To improve the results, gradient, edge and shape constraints were applied to the ROIs before final refinement using morphological operations.Results from hGReS and 3 other automated segmentation methods using edge detection, region growth and level set were compared to manual contouring. Results:For the first patient, hGReS resulted in the organ segmentation accuracy as measure by the Dices index (0.77) for the pancreas. The accuracy was slightly superior to the level set method (0.72), and both are significantly more accurate than the edge detection (0.53) and region growth methods (0.42). For the second healthy volunteer, hGReS reliably segmented the pancreatic region, achieving a Dices index of 0.82, 0.92 and 0.93 for the pancreas, stomach and liver, respectively, comparing to manual segmentation. Motion trajectories derived from the hGReS, level set and manual segmentation methods showed high correlation to respiratory motion calculated using a lung blood vessel as the reference while the other two methods showed substantial motion tracking errors. hGReS was 10 times faster than level set.Conclusion:We have shown the feasibility of automated segmentation of the pancreas anatomy based on dynamic MRI.
SU‐E‐J‐175: Proton Dose Calculation On Scatter‐Corrected CBCT Image: Feasibility Study for Adaptive Proton Therapy
Authors: Park Y , Winey B , Sharp G 
Published: July 2014

Purpose:To demonstrate feasibility of proton dose calculation on scattercorrected CBCT images for the purpose of adaptive proton therapy.Methods:Two CBCT image sets were acquired from a prostate cancer patient and a thorax phantom using an on‐board imaging system of an Elekta infinity linear accelerator. 2‐D scatter maps were estimated using a previously introduced CT‐based technique, and were subtracted from each raw projection image. A CBCT image set was then reconstructed with an open source reconstruction toolkit (RTK). Conversion from the CBCT number to HU was performed by soft tissue‐based shifting with reference to the plan CT. Passively scattered proton plans were simulated on the plan CT and corrected/uncorrected CBCT images using the XiO treatment planning system. For quantitative evaluation, water equivalent path length (WEPL) was compared in those treatment plans.Results:The scatter correction method significantly improved image quality and HU accuracy in the prostate case where large scatter artifacts were obvious. However, the correction technique showed limited effects on the thorax case that was associated with fewer scatter artifacts. Mean absolute WEPL errors from the plans with the uncorrected and corrected images were 1.3 mm and 5.1 mm in the thorax case and 13.5 mm and 3.1 mm in the prostate case. The prostate plan dose distribution of the corrected image demonstrated better agreement with the reference one than that of the uncorrected image.Conclusion:A priori CT‐based CBCT scatter correction can reduce the proton dose calculation error when large scatter artifacts are involved. If scatter artifacts are low, an uncorrected CBCT image is also promising for proton dose calculation when it is calibrated with the soft‐tissue based shifting.
SU‐E‐J‐176: Results of Images Acquired with Backscattered MV Radiation Using a Pinhole Collimator
Authors: Bernard D , Turian J , Wu Z , Darwish N , Chu J , Bernard D 
Published: July 2014

Purpose:To ascertain the feasibility of acquiring real time images of small lung tumors from scattered photons while undergoing radiation treatment. There are several methodologies currently used to track tumor location such as MV‐cine acquisition and kV fluoroscopy. However, MVcine offers no information parallel to the beam axis while kV fluoroscopy offers little potential for soft tissue discernability while also increasing the patient dose. This study investigates the feasibility of observing an actual simulated tumor while exploring techniques that may improve image quality.Methods:A prototype imager consisting of a gamma camera pinhole collimator and a computed radiography (CR) plate were used in conjunction with a Varian TrueBeam linac. One study consisted of a 2.5 cm diameter solid water cylinder representing a solid tumor imbedded within a lung equivalent material slab. The cylinder with the lung slab was sandwiched between 1 cm lung equivalent slabs and these were sandwiched between 2 slabs of solid water. The top water slab was 1 cm thick. The other imaging study consisted of three different density plugs, 0.46, 1.09, and 1.82 g/cm3 placed on the accelerator couch. The gantry was orientated 70° relative to the CR plate. The slabs and plugs were irradiated with 2000 MU and 500 MU respectively using the 6FFF mode.Results:The solid water plug was visually discernible in the slab phantom. The ratio of the signal coming from the higher density plugs (placed on the treatment couch) to that between the plugs increased from 1.02 to about 3.0 after subtracting the background image acquired with no plugs present.Conclusion:Preliminary results indicate that a lung tumor could be visualized with scattered radiation during treatment. Improvements in discerning an object can be enhanced by filtering out the head leakage and background scattered radiation not emanating from the imaged object.
SU‐E‐J‐177: Understanding the Seminal Vesicle's Motion Relative to the Prostate: Range and Pattern
Authors: Sheng Y , Li T , Yin F , Ge Y , Wu Q 
Published: July 2014

Purpose:To investigate inter‐fractional (inter‐fx) and intra‐fractional (intra‐fx) seminal vesicle (SV) motion to determine motion management strategies for prostate SBRT.Methods:9 prostate SBRT patients (37Gy/5fx) were studied. All patients were implanted with fiducial markers in the prostate for soft tissue tracking. SVs were contoured on 5 pairs of preand post‐treatment CBCTs and the planning CT. All CT/CBCT images were registered according to fiducial markers. Inter‐fx motion was analyzed by comparing pre‐treatment CBCT with planning CT; intra‐fx motion was analyzed by comparing pre‐ and post‐treatment CBCTs. Both the center of mass (COM) and boarders of SV were assessed to determine motion ranges. SV were segmented into left SV (LSV) and right SV (RSV) to analyze independent motion patterns.Results:Inter‐fx SV motion is significant in all directions. The 95% range of COM is 9.4, 14.3 and 10.3 mm for LR, AP and SI direction. Larger motion variation is observed with SV boarder. A 5 mm margin can provide 60% and 58% CTV coverage for COM and border. Intra‐fx SV motion is smaller than inter‐fx. A 5 mm margin can provide 93% and 84% CTV coverage for COM and boarder. LSV and RSV show different motion patterns in LR direction with correlation of −0.194 for COM while AP motion is strongly correlated (0.837). SV COM shows weak correlation with RSV COM, LSV COM, right boarder of RSV and left boarder of LSV (coefficient of 0.326, 0.450, 0.087, −0.192). SV COM's AP motion is strongly correlated with both LSV and RSV.Conclusion:SV moves substantially both inter‐ and intra‐fractionally, indicating the difficulty of covering CTV with fixed 5mm margin. Additional considerations/strategies in margin design are required. SV boarder motion shows independence from COM, indicating potential underdose to CTV if tracking with COM. Soft tissue imaging is highly desired for SV localization.
SU‐E‐J‐178: A Normalization Method Can Remove Discrepancy in Ventilation Function Due to Different Breathing Patterns
Authors: Qu H , Yu N , Stephans K , Xia P 
Published: July 2014

Purpose:To develop a normalization method to remove discrepancy in ventilation function due to different breathing patterns.Methods:Twenty five early stage non‐small cell lung cancer patients were included in this study. For each patient, a ten phase 4D‐CT and the voluntarily maximum inhale and exhale CTs were acquired clinically and retrospectively used for this study. For each patient, two ventilation maps were calculated from voxel‐to‐voxel CT density variations from two phases of the quiet breathing and two phases of the extreme breathing. For the quiet breathing, 0% (inhale) and 50% (exhale) phases from 4D‐CT were used. An in‐house tool was developed to calculate and display the ventilation maps. To enable normalization, the whole lung of each patient was evenly divided into three parts in the longitude direction at a coronal image with a maximum lung cross section. The ratio of cumulated ventilation from the top one‐third region to the middle one‐third region of the lung was calculated for each breathing pattern. Pearson's correlation coefficient was calculated on the ratios of the two breathing patterns for the group.Results:For each patient, the ventilation map from the quiet breathing was different from that of the extreme breathing. When the cumulative ventilation was normalized to the middle one‐third of the lung region for each patient, the normalized ventilation functions from the two breathing patterns were consistent. For this group of patients, the correlation coefficient of the normalized ventilations for the two breathing patterns was 0.76 (p < 0.01), indicating a strong correlation in the ventilation function measured from the two breathing patterns.Conclusion:For each patient, the ventilation map is dependent of the breathing pattern. Using a regional normalization method, the discrepancy in ventilation function induced by the different breathing patterns thus different tidal volumes can be removed.
SU‐E‐J‐179: Prediction of Pelvic Nodal Coverage Using Mutual Information Between Cone‐Beam and Planning CTs
Authors: Jani S , Kishan A , O' Connell D , King C , Steinberg M , Low D , Lamb J 
Published: July 2014

Purpose:To investigate if pelvic nodal coverage for prostate patients undergoing intensity modulated radiotherapy (IMRT) can be predicted using mutual image information computed between planning and cone‐beam CTs (CBCTs).Methods:Four patients with high‐risk prostate adenocarcinoma were treated with IMRT on a Varian TrueBeam. Plans were designed such that 95% of the nodal planning target volume (PTV) received the prescription dose of 45 Gy (N=1) or 50.4 Gy (N=3). Weekly CBCTs (N=25) were acquired and the nodal clinical target volumes and organs at risk were contoured by a physician. The percent nodal volume receiving prescription dose was recorded as a ground truth. Using the recorded shifts performed by the radiation therapists at the time of image acquisition, CBCTs were aligned with the planning kVCT. Mutual image information (MI) was calculated between the CBCT and the aligned planning CT within the contour of the nodal PTV. Due to variable CBCT fields‐of‐view, CBCT images covering less than 90% of the nodal volume were excluded from the analysis, resulting in the removal of eight CBCTs.Results:A correlation coefficient of 0.40 was observed between the MI metric and the percent of the nodal target volume receiving the prescription dose. One patient's CBCTs had clear outliers from the rest of the patients. Upon further investigation, we discovered image artifacts that were present only in that patient's images. When those four images were excluded, the correlation improved to 0.81.Conclusion:This pilot study shows the potential of predicting pelvic nodal dosimetry by computing the mutual image information between planning CTs and patient setup CBCTs. Importantly, this technique does not involve manual or automatic contouring of the CBCT images. Additional patients and more robust exclusion criteria will help validate our findings.