bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐J‐274: Image Distortion Quantification and Image Registration QA in GammaKnife Radiosurgery Using A Modus GRID3D Phantom
Authors: Lu L , Noa K , Woods K , Weldon M , Gupta N 
Published: July 2014

Purpose:To quantify image distortion in MRI and CT images used in GammaKnife radiosurgery planning with a Modus GRID3D phantom.Methods:Image distortion in GammaKnife radiosurgery can affect treatment efficacy by inaccurately depicting tumors and organs at risk in the brain. It is therefore important that a quantified QA check on image distortion be performed periodically. A commercial 3‐dimensional grid phantom and its associated software, GRID3D (Modus Medical Devices Inc.), was used in determining image distortion on the MRI machines and the CT‐simulator that are used clinically for GammaKnife treatment planning. The GammaKnife head frame and frame box were placed on the phantom and imaged on each MRI and CT machine according to GammaKnife imaging protocols used clinically at our institution. The obtained images were imported into the GRID3D Image Distortion Analysis System where the distortion of each image set was calculated. The calculation works by quantifying the 3D spatial deviation between the reconstructed image sets and the program's reference phantom. For registration QA, the CT and MR image sets were registered with each other. The regular analysis of grids alignment allows us to evaluate the quality of image registration from MRI to CT (commonly used in the Gamma Knife preplan scheme) and vice versa.Results:Distortion analysis using the GRID3D phantom numerically represented image distortion in the x, y, and z direction for each MRI machine and CT simulator used clinically for GammaKnife treatments. The spatial deviation between images in each direction is generally less than or equal to 1 mm when the imager is functioning properly. Image registration QA using the GRID3D phantom proves to be very efficient.Conclusion:The quantified image distortion check is important and should be incorporated into routine QA practice. It is especially important to perform this check immediately after a major machine upgrade.
SU‐E‐J‐275: Impact of the Intra and Inter Observer Variability in the Delineation of Parotid Glands On the Dose Calculation During Head and Neck Helical Tomotherapy
Authors: Jodda A , Piotrowski T 
Published: July 2014

Purpose:The intra‐ and inter‐observer variability in delineation of the parotids on the kilo‐voltage computed tomography (kVCT) and mega‐voltage computed tomography (MVCT) were examined to establish their impact on the dose calculation during adaptive head and neck helical tomotherapy (HT).Methods:Three observers delineated left and right parotids for ten randomly selected patients with oropharynx cancer treated on HT. The pre‐treatment kVCT and the MVCT from the first fraction of irradiation were selected to delineation. The delineation procedure was repeated three times by each observer. The parotids were delineated according to the institutional protocol. The analyses included intra‐observer reproducibility and inter‐structure, ‐observer and ‐modality variability of the volume and dose.Results:The differences between the left and right parotid outlines were not statistically significant (p>0.3). The reproducibility of the delineation was confirmed for each observer on the kVCT (p>0.2) and on the MVCT (p>0.1). The inter‐observer variability of the outlines was significant (p<0.001) as well as the inter‐modality variability (p<0.006). The parotids delineated on the MVCT were 10% smaller than on the kVCT. The inter‐observer variability of the parotids delineation did not affect the average dose (p=0.096 on the kVCT and p=0.176 on the MVCT). The dose calculated on the MVCT was higher by 3.3% than dose from the kVCT (p=0.009).Conclusion:Usage of the institutional protocols for the parotids delineation reduces intra‐observer variability and increases reproducibility of the outlines. These protocols do not eliminate delineation differences between the observers, but these differences are not clinically significant and do not affect average doses in the parotids. The volumes of the parotids delineated on the MVCT are smaller than on the kVCT, which affects the differences in the calculated doses.
SU‐E‐T‐05: A 2D EPID Transit Dosimetry Model Based On An Empirical Quadratic Formalism
Authors: Tan Y , Metwaly M , Glegg M , Baggarley S , Elliott A 
Published: July 2014

Purpose:To describe a 2D electronic portal imaging device (EPID) transit dosimetry model, based on an empirical quadratic formalism, that can predict either EPID or in‐phantom dose distribution for comparisons with EPID captured image or treatment planning system (TPS) dose respectively.Methods:A quadratic equation can be used to relate the reduction in intensity of an exit beam to the equivalent path length of the attenuator. The calibration involved deriving coefficients from a set of dose planes measured for homogeneous phantoms with known thicknesses under reference conditions. In this study, calibration dose planes were measured with EPID and ionisation chamber (IC) in water for the same reference beam (6MV, 100mu, 20×20cm2) and set of thicknesses (0–30cm). Since the same calibration conditions were used, the EPID and IC measurements can be related through the quadratic equation. Consequently, EPID transit dose can be predicted from TPS exported dose planes and in‐phantom dose can be predicted using EPID distribution captured during treatment as an input. The model was tested with 4 open fields, 6 wedge fields, and 7 IMRT fields on homogeneous and heterogeneous phantoms. Comparisons were done using 2D absolute gamma (3%/3mm) and results were validated against measurements with a commercial 2D array device.Results:The gamma pass rates for comparisons between EPID measured and predicted ranged from 93.6% to 100.0% for all fields and phantoms tested. Results from this study agreed with 2D array measurements to within 3.1%. Meanwhile, comparisons in‐phantom between TPS computed and predicted ranged from 91.6% to 100.0%. Validation with 2D array device was not possible for inphantom comparisons.Conclusion:A 2D EPID transit dosimetry model for treatment verification was described and proven to be accurate. The model has the advantage of being generic and allows comparisons at the EPID plane as well as multiple planes in‐phantom.
SU‐E‐T‐09: A Dosimetric Analysis of Various Clinically Used Bolus Materials
Authors: Stowe M , Yeager C , Zhou F , Hand C 
Published: July 2014

Purpose:To evaluate the dosimetric effect of various clinically used bolus materials.Methods:Materials investigated include solid water, superflab, wet gauze, wet sheets, Play‐Doh™, and gauze embedded with petroleum jelly. Each bolusing material was scanned in a Philips CT to determine the Hounsfield unit (HU) and to verify uniformity throughout the material. Using the corresponding HU, boluses of 0.5 cm and 1.0 cm thicknesses were created in the Eclipse treatment planning system (TPS) on a solid water phantom. Dose was calculated at various depths for beam energies 6 MV, 6 MeV, 9 MeV, and 12 MeV to determine the effects of each material on deposition of dose. In addition, linac‐based measurements at these energies were made using a farmer chamber in solid water. Wet sheets and wet gauze were measured with various water content to quantify the effects on dose.Results:Preliminary CT scans find a range in HU of bolus materials from −120 to almost 300. There is a trend in the dose at depth based on the HU of the material; however inconsistencies are found when the bolus materials have a negative HU value. The measured data indicates that there is a linear relationship between the mass of water in a material and the dose reading, the slope of which is material dependent.Conclusion:Due to the variation in HU of the bolus materials studied, it is recommended that any new bolus be evaluated before clinical use to determine physical and dosimetric properties. If possible, patients should have bolus included in their CT scans; or if the bolus is created in the TPS, the HU should correspond to the material used. For water‐soaked materials, once the bolus material is selected (gauze or sheet), the bolusing effect is only dependent on the amount of water applied to the material.
SU‐E‐T‐12: A Feasibility Study of Patient Specific QA Using Gafchromic Film of Dynamic Feathering in Junctions of Craniospinal Irradiation
Authors: Stanford J , Duggar W , Yang C 
Published: July 2014

Purpose:Cranio‐spinal irradiation is the most complicated format of the conventional external beam radiation therapy because it involves matches of non‐coplanar beams which are susceptible to daily setup errors. This study explores the efficacy of Gafchromic film dosimetry to quantitatively verify the junctions for cranio‐spinal radiation feathered with field in field technique.Methods:15cm in thickness of solid water phantom was scanned vertically and exported to the Pinnacle TPS as primary phantom data set. A patient cranio‐spinal plan, consisted of two bilateral whole brain beams dynamically matched with a posterior spinal beam using field in field technique, was transferred to the phantom and recalculated for one fraction with set monitor units identical to the original plan. Next, planar dose distribution on the phantom was exported to the FilmQA Pro 2013 software (Ashland, Inc.) in binary format for comparison with the measured dose distribution. An EBT2 film was sandwiched in the middle of the phantom and the phantom was set up according to the QA plan based on the room laser system. The shifts instructions associated with the patient original plan were made and the beams from the patient original plan delivered to the solid water phantom via the record and verify system in QA mode. The dose distribution from the measured film was compared with the planned reference distribution using gamma analysis and profile comparison.Results:Gamma passing rate of 91 % with DTA 3mm and 5% dose difference was obtained within the junction region, significantly greater passing rate above 95 % was obtained in the homogeneous region of the brain field.Conclusion:This study confirms that Gafchromic film dosimetry can be used to validate the efficacy of FIF feathering technique for cranio‐spinal treatment. FIF technique with Gafchromic dosimetry may now be the new standard for delivering efficient and accurate cranio‐spinal radiation with confidence.
SU‐E‐T‐21: A Novel Sampling Algorithm to Reduce Intensity‐Modulated Radiation Therapy (IMRT) Optimization Time
Authors: Tiwari P , Xie Y , Chen Y , Deasy J 
Published: July 2014

Purpose:The IMRT optimization problem requires substantial computer time to find optimal dose distributions because of the large number of variables and constraints. Voxel sampling reduces the number of constraints and accelerates the optimization process, but usually deteriorates the quality of the dose distributions to the organs. We propose a novel sampling algorithm that accelerates the IMRT optimization process without significantly deteriorating the quality of the dose distribution.Methods:We included all boundary voxels, as well as a sampled fraction of interior voxels of organs in the optimization. We selected a fraction of interior voxels using a clustering algorithm, that creates clusters of voxels that have similar influence matrix signatures. A few voxels are selected from each cluster based on the pre‐set sampling rate.Results:We ran sampling and no‐sampling IMRT plans for de‐identified head and neck treatment plans. Testing with the different sampling rates, we found that including 10% of inner voxels produced the good dose distributions. For this optimal sampling rate, the algorithm accelerated IMRT optimization by a factor of 2–3 times with a negligible loss of accuracy that was, on average, 0.3% for common dosimetric planning criteria.Conclusion:We demonstrated that a sampling could be developed that reduces optimization time by more than a factor of 2, without significantly degrading the dose quality.
SU‐E‐T‐25: A Study of the Optimal PTV Margin for Patients Receiving CBCT‐Guided Prostate IMRT Based On CBCT Dose Calculation
Authors: Gill S , Pearson D , Dalhart A , Reddy K , Chen C 
Published: July 2014

Purpose:Variation in daily setup and rectum/bladder filling leads to uncertainties in the delivery of prostate IMRT. To determine the optimal PTV margin for CBCT‐guided prostate IMRT, daily CBCTs were used to estimate prostate and OAR doses, compared to those expected from planning.Methods:Patients diagnosed with prostate cancer were treated with prostate IMRT to 70Gy in 28 fractions. Daily CBCT was utilized for image guidance. The prostate CTV and OARs were contoured on all CBCTs. IMRT plans were created using 1 mm, 3 mm, 5 mm and 7 mm CTV to PTV margins. Dosimetric analysis of the plans following daily CBCT translational shifts was performed.Results:28 CBCT sessions were evaluated for preliminary results. Planned prostate CTV V100% was 100% for all PTV margins. Based on CBCT analysis, the actual cumulative V100% was 96.65±4.73%, 98.82±2.72%, 99.86±0.53% and 99.96±0.11% for 1‐, 3‐, 5‐ and 7 mm margins, respectively. The planned rectum V70Gy was 0.88%, 2.67%, 6.02% and 13.42%, for 1‐mm, 3‐mm, 5‐mm and 7‐mm PTV margins. The actual cumulative V70Gy for the rectum was 5.47±2.7%, 9.64±3.12%, 13.68±3.39% and 20.82±3% for 1‐, 3‐, 5‐ and 7 mm margins, respectively. The planned vs. delivered rectum V60 Gy was 6.99 vs. 14.73±3.63% (1 mm), 9.83 vs. 18.43±3.73% (3), 13.61 vs. 22.5±3.86% (5) and 23.20 vs. 30.82±4 % (7). The planned vs. delivered bladder V70Gy was 0.01%, 0.24%, 0.98% and 1.75% vs. 0.24±0.25%, 0.93±0.69%, 2.46±1.36% and 4.07±2% for 1‐, 3‐, 5‐ and 7 mm margins, respectively.Conclusion:Daily setup variation during prostate IMRT yields differences in the actual vs. expected doses received by the prostate CTV, rectum and bladder. The magnitude of these differences is significantly affected by the PTV margin utilized. A 3–5 mm PTV margin appears to be optimal for prostate IMRT when daily CBCT is used for image guidance.
SU‐E‐T‐29: A Web Application for GPU‐Based Monte Carlo IMRT/VMAT QA with Delivered Dose Verification
Authors: Folkerts M , Graves Y , Tian Z , Gu X , Jia X , Jiang S 
Published: July 2014

Purpose:To enable an existing web application for GPU‐based Monte Carlo (MC) 3D dosimetry quality assurance (QA) to compute “delivered dose” from linac logfile data.Methods:We added significant features to an IMRT/VMAT QA web application which is based on existing technologies (HTML5, Python, and Django). This tool interfaces with python, c‐code libraries, and command line‐based GPU applications to perform a MC‐based IMRT/VMAT QA. The web app automates many complicated aspects of interfacing clinical DICOM and logfile data with cutting‐edge GPU software to run a MC dose calculation. The resultant web app is powerful, easy to use, and is able to re‐compute both plan dose (from DICOM data) and delivered dose (from logfile data). Both dynalog and trajectorylog file formats are supported. Users upload zipped DICOM RP, CT, and RD data and set the expected statistic uncertainty for the MC dose calculation. A 3D gamma index map, 3D dose distribution, gamma histogram, dosimetric statistics, and DVH curves are displayed to the user. Additional the user may upload the delivery logfile data from the linac to compute a “delivered dose” calculation and corresponding gamma tests. A comprehensive PDF QA report summarizing the results can also be downloaded.Results:We successfully improved a web app for a GPU‐based QA tool that consists of logfile parcing, fluence map generation, CT image processing, GPU based MC dose calculation, gamma index calculation, and DVH calculation. The result is an IMRT and VMAT QA tool that conducts an independent dose calculation for a given treatment plan and delivery log file. The system takes both DICOM data and logfile data to compute plan dose and delivered dose respectively.Conclusion:We sucessfully improved a GPU‐based MC QA tool to allow for logfile dose calculation. The high efficiency and accessibility will greatly facilitate IMRT and VMAT QA.
SU‐E‐T‐33: An EPID‐Based Method for Testing Absolute Leaf Position for MLC Without Backup Jaws
Authors: Hancock S , Whitaker M 
Published: July 2014

Purpose:Methods in common use for MLC leaf position QA are limited to measurements relative to an arbitrary reference position. The authors previously presented an EPID‐based method for efficiently testing accuracy of leaf position relative to the mechanical isocenter for MLC with backup jaws. The purpose of this work is to extend that method to the general case of MLC without backup jaws.Methods:A pair of collimator walkout images is used to determine the location of the mechanical isocenter relative to the center of one field using a parameter called X‐offset. The method allows for shift of the imager panel to cover subsets of MLC leaves within the limited field of view of the imager. For a shifted panel position, an image of three beam strips defined by a subset of MLC leaves allows determination of the position of each leaf relative to the isocenter. The location of the isocenter is determined by applying X‐offset to an image of a single rectangular field obtained at that panel position. The method can also be used to test backup jaws instead of MLC leaves. A software tool was developed to efficiently analyze the images.Results:The software tool reports leaf position and deviation from nominal position, and provides visual displays to facilitate rapid qualitative interpretation. Test results using this method agree well with results using the previous method requiring backup jaws. Test results have been successfully used to recalibrate one model MLC (Elekta MLCi2™). Work in progress includes extension of the software tool to other MLC models, and quantification of reproducibility of the measurements.Conclusion:This work successfully demonstrates a method to efficiently and accurately measure MLC leaf position, or backup jaw position, relative to the mechanical isocenter of the collimator.
SU‐E‐T‐34: An in Vivo Study On Pulsed Low Dose‐Rate Radiotherapy for Prostate Cancer
Authors: Wang B , Cvetkovic D , Chen X , Zhang P , Zhang C , Chen L , Ma C 
Published: July 2014

Purpose:Re‐irradiation with conventional radiotherapy techniques (CRT) may pose significant risks due to high accumulative radiation doses. Pulsed low dose‐rate radiotherapy (PLDR) has been used in clinical trials for recurrent cancer treatment. In our previous studies, PLDR irradiation showed significantly lower toxicity than CRT, resulting in much longer survival of mice after PLDR total body irradiation (TBI) than conventional TBI. The purpose of this study was to investigate tumor control efficacy of PLDR treatment for prostate cancer with an animal model of prostate cancer LNCaP.Methods:We used an orthotopic murine model of LNCaP cell line for this study. LNCaP cells were implanted into immune‐suppressed male nude mice via surgery. We monitored the tumor growth with MRI. The tumor‐bearing mice were allocated into a PLDR(n=9), CRT(n=7), and control group(n=7) randomly. The mice in the PLDR and CRT groups were irradiated with 2Gy dose for one time. For the CRT treatment, the mice received 2Gy at a dose‐rate of 300 MU/minute. For the PLDR treatment, the 2Gy dose was further divided into ten pulses of 0.2Gy at the same dose‐rate with an interval of 3 minutes between the pulses.Results:Sizable tumor growth delays were observed for the PLDR and CRT groups through weekly MRI scans. The mean values of the normalized tumor volumes (± standard deviation of the mean) were 1.53±0.07, 1.53±0.14, and 1.81±0.09 at one week after treatment, 2.28±0.13, 2.19±0.16, and 3.04±0.25 at two weeks after treatment, and 3.31±0.23, 3.14±0.24 and 4.62±0.49 at three weeks after treatment, for the PLDR, CRT, and control groups, respectively.Conclusion:The PLDR and CRT treatments showed comparable tumor control rates in this study. Our in vivo results indicate that PLDR may be a viable option for treating recurrent prostate cancer due to its equivalent tumor control but low normal tissue toxocities.
SU‐E‐T‐35: An Investigation of the Accuracy of Cervical IMRT Dose Distribution Using 2D/3D Ionization Chamber Arrays System and Monte Carlo Simulation
Authors: Zhang Y , Liu D , Yang J , Liu H 
Published: July 2014

Purpose:The purpose of this work is to compare the verification results of three solutions (2D/3D ionization chamber arrays measurement and Monte Carlo simulation), the results will help make a clinical decision as how to do our cervical IMRT verification.Methods:Seven cervical cases were planned with Pinnacle 8.0m to meet the clinical acceptance criteria. The plans were recalculated in the Matrixx and Delta4 phantom with the accurate plans parameters. The plans were also recalculated by Monte Carlo using leaf sequences and MUs for individual plans of every patient, Matrixx and Delta4 phantom. All plans of Matrixx and Delta4 phantom were delivered and measured. The dose distribution of iso slice, dose profiles, gamma maps of every beam were used to evaluate the agreement. Dose‐volume histograms were also compared.Results:The dose distribution of iso slice and dose profiles from Pinnacle calculation were in agreement with the Monte Carlo simulation, Matrixx and Delta4 measurement. A 95.2%/91.3% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Pinnacle distributions within 3mm/3% gamma criteria. A 96.4%/95.6% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Monte Carlo simulation within 2mm/2% gamma criteria, almost 100% gamma pass ratio within 3mm/3% gamma criteria. The DVH plot have slightly differences between Pinnacle and Delta4 measurement as well as Pinnacle and Monte Carlo simulation, but have excellent agreement between Delta4 measurement and Monte Carlo simulation.Conclusion:It was shown that Matrixx/Delta4 and Monte Carlo simulation can be used very efficiently to verify cervical IMRT delivery. In terms of Gamma value the pass ratio of Matrixx was little higher, however, Delta4 showed more problem fields. The primary advantage of Delta4 is the fact it can measure true 3D dosimetry while Monte Carlo can simulate in patients CT images but not in phantom.
SU‐E‐T‐39: Analyses of Plan Quality Using Different Gantry Rotation Time On Volumetric Modulated Arc Therapy in Rectal Carcinoma
Authors: Chi Z , Li R , qiu r , cao y , Han C 
Published: July 2014

Purpose:To compare plan quality of volumetric modulated arc radiotherapy (VMAT) using different gantry rotation times.Methods:In ten rectal carcinoma patients, plans with different gantry rotation times were designed by Oncentra4.3 planning system, each of them was optimized by experienced planners using almost similar parameters and dose constraints except the different gantry rotation time. The gantry rotation time was increased from 30s to 150s by step of 30(30s, 60s, 90s, 120s, and 150s). Plans (VMAT30s, VMAT60s, VMAT90s, VMAT120s and VMAT150s) were normalized so that at least 95% of PTV would receive the prescription dose 50 Gray in 25 fractions. Dose‐volume histograms and isodose distributions were evaluated. Conformity indices (CI), homogeneous indices (HI), monitor units (MUs), delivery time were also compared.Results:As the increasing of gantry rotation time, VMAT150s provided comparable organs at risk sparing and better target coverage and conformity than VMAT30s. In the normal tissue such as bladder and femurs, the VMAT plans show almost the same V30 and Dmean for them compared with IMRT plans, meanwhile the conformity indices (CI) was better than IMRT plans(p=0.021). However, there was no significant different among the VMAT60s, VMAT90s, VMAT120s and VMAT150s (p=0.054). VMAT150s increased delivery time and monitor units in plans without improving plan quality compared to VMAT60s, VMAT90s and VMAT120s.Conclusion:VMAT60s, VMAT90s, VMAT120s and VMAT150s achieved comparable treatment plans in rectal carcinoma. Slower gantry movement in VMAT150s only improves slight improvement than the others.