bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐324: The Influence of Patient Positioning Uncertainties in Proton Radiotherapy On Proton Range and Dose Distributions
Authors: Liebl J , Paganetti H , Winey B 
Published: July 2014

Purpose:Proton radiotherapy allows radiation treatment delivery with high dose gradients. The nature of such dose distributions increases the influence of patient positioning uncertainties on their fidelity when compared to photon radiotherapy. The present work quantitatively analyzes the influence of setup uncertainties on proton range and dose distributions.Methods:38 clinical passive scattering treatment fields for small lesions in the head were studied. Dose distributions for shifted and rotated patient positions were Monte Carlo‐simulated. Proton range uncertainties at the 50% and 90%‐dose falloff position were calculated considering 18 arbitrary combinations of maximal patient position shifts and rotations for two patient positioning methods. Normal tissue complication probabilities (NTCPs), equivalent uniform doses (EUDs) and tumor control probabilities (TCPs) were studied for organs at risk (OARs) and target volumes of eight patients.Results:We identified a median 1σ proton range uncertainty at the 50%‐dose falloff of 2.8 mm for anatomy‐based patient positioning and 1.6 mm for fiducial‐based patient positioning as well as 7.2 mm and 5.8 mm for the 90%‐dose falloff position respectively. These range uncertainties were correlated to heterogeneity indices (HIs) calculated for each treatment field (38% < R2 < 50%). A NTCP increase of more than 10% (absolute) was observed for less than 2.9% (anatomy‐based positioning) and 1.2% (fiducial‐based positioning) of the studied OARs and patient shifts. TCP decreases larger than 10% (absolute) were seen for less than 2.2% of the target volumes or non‐existent. EUD changes were up to 178% for OARs and 35% for target volumes.Conclusion:The influence of patient positioning uncertainties on proton range in therapy of small lesions in the human brain and target and OAR dosimetry were studied. Observed range uncertainties were correlated with HIs. The clinical practice of using multiple compensator‐smeared treatment beams selected to avoid distal OAR sparing is considered to be safe.J. L. was supported by a scholarship of the University of Vienna
SU‐F‐BRF‐06: Density Correction for Deformable Image Registration to Improve CT Number Mapping
Authors: Yang J , Zhang Y , Zhang L , Balter P , Court L 
Published: July 2014

Purpose:To improve the accuracy of CT number mapping inside the lung using deformable image registration for cases having substantially large lung volume differences.Methods:The deep‐inspiration‐breath‐hold (DIBH) CT image and the end‐of‐exhalation (EE) phase image in 4DCT of three thoracic cancer patients were enrolled in this study. The lung volumes were manually delineated and the lung volume ratio of DIBH‐CT over EECT is 1.7, 1.8, and 2.0 respectively, demonstrating large volume differences. A demons‐based deformable registration was first applied to register the EECT to the DIBH‐CT for each patient, and the resulting deformation field deformed the EE‐CT image to the DIBH‐CT space. Based on the assumption that the mass of lung remains the same during respiration, we created a mass preserving model to correlate the lung density variations with the lung volumetric changes, which were characterized by the Jacobian derived from the deformation field. The Jacobian is used to correct the lung CT number transferred from the EE‐CT image. The deformed images with and without the density correction were compared using absolute intensity difference created by subtracting the deformed image from the DIBH‐CT image.Results:The deformable registration could register the lung shape very well, but the CT numbers inside the lung could not be registered correctly. Without density correction, the mean and standard deviation of the absolute CT number difference inside the lung were 59±48, 69±49, and 71±42 for the three cases. After density correction, these numbers changed to 18±35, 20±35, and 14±29, respectively, demonstrating an improvement in the accuracy of CT number mapping. The accumulative histogram of the intensity difference also showed that density correction improved CT number mapping.Conclusion:Density correction improved the CT number mapping inside the lung using deformable image registration for difficult cases having large lung volume differences.This work is partially supported by the CPRIT (Cancer Prevention Research Institute of Texas) grant RP110732.
SU‐F‐BRF‐14: Increasing the Accuracy of Dose Calculation On Cone‐Beam Imaging Using Deformable Image Registration in the Case of Prostate Translation
Authors: Fillion O , Gingras L , Archambault L 
Published: July 2014

Purpose:Artifacts can reduce the quality of dose re‐calculations on CBCT scans during a treatment. The aim of this project is to correct the CBCT images in order to allow for more accurate and exact dose calculations in the case of a translation of the tumor in prostate cancer.Methods:Our approach is to develop strategies based on deformable image registration algorithms using the elastix software (Klein et al., 2010) to register the treatment planning CT on a daily CBCT scan taken during treatment. Sets of images are provided by a 3D deformable phantom and comprise two CT and two CBCT scans: one of both with the reference anatomy and the others with known deformations (i.e. translations of the prostate). The reference CT is registered onto the deformed CBCT and the deformed CT serves as the control for dose calculation accuracy. The planned treatment used for the evaluation of dose calculation is a 2‐Gy fraction prescribed at the location of the reference prostate and assigned to 7 rectangular fields.Results:For a realistic 0.5‐cm translation of the prostate, the relative dose discrepancy between the CBCT and the CT control scan at the prostate's centroid is 8.9 ± 0.8 % while dose discrepancy between the registered CT and the control scan lessens to −2.4 ± 0.8 %. For a 2‐cm translation, clinical indices like the V90 and the D100 are more accurate by 0.7 ± 0.3 % and 8.0 ± 0.5 cGy respectively when using registered CT than when using CBCT for dose calculation.Conclusion:The results show that this strategy gives doses in agreement within a few percents with those from calculations on actual CT scans. In the future, various deformations of the phantom anatomy will allow a thorough characterization of the registration strategies needed for more complex anatomies.
SU‐F‐18C‐02: Evaluations of the Noise Power Spectrum of a CT Iterative Reconstruction Technique for Radiation Therapy
Authors: Dolly S , Chen H , Anastasio M , Mutic S , Li H 
Published: July 2014

Purpose:To quantitatively assess the noise power spectrum (NPS) of the new, commercially released CT iterative reconstruction technique, iDose4 from Philips, to compare it with filtered back‐projection techniques (FBP), and to provide clinical practice suggestions for radiation therapy.Methods:A uniform phantom was CT imaged with 120kVp tube potential over a range of mAs (250‐3333). The image sets were reconstructed using two reconstruction algorithms (FBP and iDose4 with noise reduction levels 1, 3, and 6) and three reconstruction filters (standard B, smooth A, and sharp C), after which NPS variations were analyzed and compared on region of interest (ROI) sizes (16×16 to 128×128 pixels), ROI radii (0–65 mm), reconstruction algorithms, reconstruction filters, and mAs.Results:The NPS magnitude and shape depended considerably on ROI size and location for both reconstruction algorithms. Regional noise variance became more stationary as ROI size decreased, minimizing NPS artifacts. The optimal 32×32‐pixel ROI size balanced the trade‐off between stationary noise and adequate sampling. NPS artifacts were greatest at the center of reconstruction space and decreased with increasing ROI distance from the center. The optimal ROI position was located near the phantom's radial midpoint (∼40mm). For sharper filters, the NPS magnitude and the maximum magnitude frequency increased. Higher dose scans yielded lower NPS magnitudes for both reconstruction algorithms and all filters. Compared to FBP, the iDose4 algorithm reduced the NPS magnitude while preferentially reducing noise at mid‐range spatial frequencies, altering noise texture. This reduction was more significant with increasing iDose4 noise reduction level.Conclusion:Compared to pixel standard deviation, NPS has greater clinical potential for task‐based image quality assessment, describing both the magnitude and spatial frequency characteristics of image noise. While iDose4 reduces the NPS magnitude more dramatically than FBP, further studies are needed to assess the impacts of noise texture alteration on its clinical usage.
SU‐F‐18C‐04: A Combination of Monoenergetic Reconstruction and Stoichiometric Calibration for Tissue Characterization Using Dual Energy Computed Tomography
Authors: Bedwani S , Tremblay J , Bouchard H 
Published: July 2014

Purpose:Dual energy computed tomography (DECT) pre‐reconstruction methods require the prior knowledge of the X‐ray source spectrum to allow extracting physical parameters needed for radiation therapy dose calculation, such as electron density (ED) and the effective atomic number (EAN). While DECT stoichiometric calibration may provide reliable performance for typical radiation therapy clinical conditions, it is yet to be adapted to prereconstruction methods. The presence of noise and inaccurate spectrum description may lead to systematic errors and artifacts which compromise the accuracy of treatment planning.Methods:A new technique is investigated which consists in applying a DECT stoichiometric calibration method to a set of monoenergetic images obtained with a DECT prereconstruction method. To evaluate the performance of this extended method, a simulation environment is developed to generate DECT scans under well controlled conditions, to reconstruct monoenergetic images of a tissue‐equivalent phantom from transformed sinograms and to extract ED and EAN maps using a DECT formalism.Result:Under simulated clinical conditions, the accuracy in determining ED with the extended method versus a pre‐reconstruction method alone is shown to be better than 0.35% versus 0.5%, respectively. In the presence of a realistic noise level, EAN determination presents a relative mean error that drops from 2.5% to 0.5% once the calibration is applied. Considering a spectrum alteration by a 1 mm Cu layer, EAN errors are up to 30% for the pre‐reconstruction method alone versus less than 3% for the extended method.Conclusion:This study shows that combining pre‐reconstruction DECT methods with a stoichiometric calibration considerably improves the accuracy and reliability of tissue characterization for radiation therapy in a clinical context. The presented method could potentially be adapted as gold standard for dose calculation methods based on DECT.
SU‐F‐18C‐08: A Validation Study of a Commercially Available Software Package's Absorbed Dose Estimates in a Physical Phantom
Authors: Supanich M , Siegelman J 
Published: July 2014

Purpose:This study assesses the accuracy of the absorbed dose estimates from CT scans generated by Monte Carlo (MC) simulation using a commercially available radiation dose monitoring software program.Methods:Axial CT studies of an anthropomorphic abdomen phantom with dose bores at a central location and 4 peripheral locations were conducted using a fixed tube current at 120 kV. A 100 mm ion chamber and a 0.6 cc ion chamber calibrated at diagnostic energy levels were used to measure dose in the phantom at each of the 5 dose bore locations. Simulations using the software program's Monte Carlo engine were run using a mathematical model of the anthropomorphic phantom to determine conversion coefficients between the CTDIvol used for the study and the dose at the location of the dose bores. Simulations were conducted using both the software's generic CT beam model and a refined model generated using HVL and bow tie filter profile measurements made on the scanner used for the study.Results:Monte Carlo simulations completed using the generalized beam model differed from the measured conversion factors by an absolute value average of 13.0% and 13.8% for the 100 mm and 0.6 cc ion chamber studies, respectively. The MC simulations using the scanner specific beam model generated conversion coefficients that differed from the CTDIvol to measured dose conversion coefficients by an absolute value average of 7.3% and 7.8% for the 100 mm and 0.6 cc ion chamber cases, respectively.Conclusion:A scanner specific beam model used in MC simulations generates more accurate dose conversion coefficients in an anthropomorphic phantom than those generated with a generalized beam model. Agreement between measured conversion coefficients and simulated values were less than 20% for all positions using the universal beam model.
SU‐F‐18C‐09: Assessment of OSL Dosimeter Technology in the Validation of a Monte Carlo Radiation Transport Code for CT Dosimetry
Authors: Carver D , Kost S , Pickens D , Price R , Stabin M 
Published: July 2014

Purpose:To assess the utility of optically stimulated luminescent (OSL) dosimeter technology in calibrating and validating a Monte Carlo radiation transport code for computed tomography (CT).Methods:Exposure data were taken using both a standard CT 100‐mm pencil ionization chamber and a series of 150‐mm OSL CT dosimeters. Measurements were made at system isocenter in air as well as in standard 16‐cm (head) and 32‐cm (body) CTDI phantoms at isocenter and at the 12 o' clock positions. Scans were performed on a Philips Brilliance 64 CT scanner for 100 and 120 kVp at 300 mAs with a nominal beam width of 40 mm. A radiation transport code to simulate the CT scanner conditions was developed using the GEANT4 physics toolkit. The imaging geometry and associated parameters were simulated for each ionization chamber and phantom combination. Simulated absorbed doses were compared to both CTDI100 values determined from the ion chamber and to CTDI100 values reported from the OSLs. The dose profiles from each simulation were also compared to the physical OSL dose profiles.Results:CTDI100 values reported by the ion chamber and OSLs are generally in good agreement (average percent difference of 9%), and provide a suitable way to calibrate doses obtained from simulation to real absorbed doses. Simulated and real CTDI100 values agree to within 10% or less, and the simulated dose profiles also predict the physical profiles reported by the OSLs.Conclusion:Ionization chambers are generally considered the standard for absolute dose measurements. However, OSL dosimeters may also serve as a useful tool with the significant benefit of also assessing the radiation dose profile. This may offer an advantage to those developing simulations for assessing radiation dosimetry such as verification of spatial dose distribution and beam width.
SU‐F‐18C‐12: On the Relationship of the Weighted Dose to the Surface Dose In Abdominal CT – Patient Size Dependency
Authors: Zhou Y , Scott A , Allahverdian J 
Published: July 2014

Purpose:It is possible to measure the patient surface dose non‐invasively using radiolucent dosimeters. However, the patient size specific weighted dose remains unknown. We attempted to study the weighted dose to surface dose relationship as the patient size varies in abdominal CT.Methods:Seven abdomen phantoms (CIRS TE series) simulating patients from an infant to a large adult were used. Size specific doses were measured with a 100 mm CT chamber under axial scans using a Siemens Sensation 64 (mCT) and a GE 750 HD. The scanner settings were 120 kVp, 200 mAs with fully opened collimations. Additional kVps (80, 100, 140) were added depending on the phantom sizes. The ratios (r) of the weighted CT dose (Dw) to the surface dose (Ds) were related to the phantom size (L) defined as the diameter resulting the equivalent cross‐sectional area.Results:The Dw versus Ds ratio (r) was fitted to a linear relationship: r = 1.083 − 0.007L (R square = 0.995), and r = 1.064 − 0.007L (R square = 0.953), for Siemens Sensation 64 and GE 750 HD, respectively. The relationship appears to be independent of the scanner specifics.Conclusion:The surface dose to the weighted dose ratio decreases linearly as the patient size increases. The result is independent of the scanner specifics. The result can be used to obtain in vivo CT dosimetry in abdominal CT.
SU‐F‐18C‐13: Low‐Dose X‐Ray CT Reconstruction Using a Hybrid First‐Order Method
Authors: Liu L , Lin W , Jin M 
Published: July 2014

Purpose:To develop a novel reconstruction method for X‐ray CT that can lead to accurate reconstruction at significantly reduced dose levels combining low X‐ray incident intensity and few views of projection data.Methods:The noise nature of the projection data at low X‐ray incident intensity was modeled and accounted by the weighted least‐squares (WLS) criterion. The total variation (TV) penalty was used to mitigate artifacts caused by few views of data. The first order primal‐dual (FOPD) algorithm was used to minimize TV in image domain, which avoided the difficulty of the non‐smooth objective function. The TV penalized WLS reconstruction was achieved by alternated FOPD TV minimization and projection onto convex sets (POCS) for data fidelity constraints. The proposed FOPD‐POCS method was evaluated using the FORBILD jaw phantom and the real cadaver head CT data.Results:The quantitative measures, root mean square error (RMSE) and contrast‐to‐noise ratio (CNR), demonstrate the superior denoising capability of WLS over LS‐based TV iterative reconstruction. The improvement of RMSE (WLS vs. LS) is 15%∼21% and that of CNR is 17%∼72% when the incident counts per ray are ranged from 1×105 to 1×103. In addition, the TV regularization can accurately reconstruct images from about 50 views of the jaw phantom. The FOPD‐POCS reconstruction reveals more structural details and suffers fewer artifacts in both the phantom and real head images. The FOPD‐POCS method also shows fast convergence at low X‐ray incident intensity.Conclusion:The new hybrid FOPD‐POCS method, based on TV penalized WLS, yields excellent image quality when the incident X‐ray intensity is low and the projection views are limited. The reconstruction is computationally efficient since the FOPD minimization of TV is applied only in the image domain. The characteristics of FOPD‐POCS can be exploited to significantly reduce radiation dose of X‐ray CT without compromising accuracy for diagnosis or treatment planning.
SU‐F‐18C‐15: Model‐Based Multiscale Noise Reduction On Low Dose Cone Beam Projection
Authors: Yao W , Farr J 
Published: July 2014

Purpose:To improve image quality of low dose cone beam CT for patient positioning in radiation therapy.Methods:In low dose cone beam CT (CBCT) imaging systems, Poisson process governs the randomness of photon fluence at x‐ray source and the detector because of the independent binomial process of photon absorption in medium. On a CBCT projection, the variance of fluence consists of the variance of noiseless imaging structure and that of Poisson noise, which is proportional to the mean (noiseless) of the fluence at the detector. This requires multiscale filters to smoothen noise while keeping the structure information of the imaged object. We used a mathematical model of Poisson process to design multiscale filters and established the balance of noise correction and structure blurring. The algorithm was checked with low dose kilo‐voltage CBCT projections acquired from a Varian OBI system.Results:From the investigation of low dose CBCT of a Catphan phantom and patients, it showed that our model‐based multiscale technique could efficiently reduce noise and meanwhile keep the fine structure of the imaged object. After the image processing, the number of visible line pairs in Catphan phantom scanned with 4 ms pulse time was similar to that scanned with 32 ms, and soft tissue structure from simulated 4 ms patient head‐and‐neck images was also comparable with scanned 20 ms ones. Compared with fixed‐scale technique, the image quality from multiscale one was improved.Conclusion:Use of projection‐specific multiscale filters can reach better balance on noise reduction and structure information loss. The image quality of low dose CBCT can be improved by using multiscale filters.
MO‐B‐16A‐02: In Memoriam of Donald D. Tolbert: Surviving the Politics of Radiation Therapy
Authors: Bayouth J , Limmer J 
Published: July 2014

Today's healthcare work environment is ever‐changing and without a doubt will continue to do so for the foreseeable future. How physicists are employed, evaluated, and valued are important aspects of our careers. With increasing demands and challenges being placed on the medical physics workforce, it is important to have the skills and knowledge to prepare for potential challenges to the status‐quo of our employment status. Surviving in a world of change, consolidation, increased workload, and financial constraints is not a given, and preparing for those changes and challenges will benefit individuals as well as the medical physics community at large.Learning Objectives:

Understand the challenges of succeeding in different work environments.
Learn strategies to help define the role of a medical physicist to various administrators, physicians, and department staff and directors.
Learn how to successfully communicate and interact with University, Hospital, and Department administrators.
MO‐E‐18C‐02: Hands‐On Monte Carlo Project Assignment as a Method to Teach Radiation Physics
Authors: Pater P , Vallieres M , Seuntjens J 
Published: July 2014

Purpose:To present a hands‐on project on Monte Carlo methods (MC) recently added to the curriculum and to discuss the students' appreciation.Methods:Since 2012, a 1.5 hour lecture dedicated to MC fundamentals follows the detailed presentation of photon and electron interactions. Students also program all sampling steps (interaction length and type, scattering angle, energy deposit) of a MC photon transport code. A handout structured in a step‐by‐step fashion guides student in conducting consistency checks. For extra points, students can code a fully working MC simulation, that simulates a dose distribution for 50 keV photons. A kerma approximation to dose deposition is assumed. A survey was conducted to which 10 out of the 14 attending students responded. It compared MC knowledge prior to and after the project, questioned the usefulness of radiation physics teaching through MC and surveyed possible project improvements.Results:According to the survey, 76% of students had no or a basic knowledge of MC methods before the class and 65% estimate to have a good to very good understanding of MC methods after attending the class. 80% of students feel that the MC project helped them significantly to understand simulations of dose distributions. On average, students dedicated 12.5 hours to the project and appreciated the balance between hand‐holding and questions/implications.Conclusion:A lecture on MC methods with a hands‐on MC programming project requiring about 14 hours was added to the graduate study curriculum since 2012. MC methods produce “gold standard” dose distributions and slowly enter routine clinical work and a fundamental understanding of MC methods should be a requirement for future students. Overall, the lecture and project helped students relate crosssections to dose depositions and presented numerical sampling methods behind the simulation of these dose distributions.Research funding from governments of Canada and Quebec. PP acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290)