bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐375: Evaluation of a MapCHECK2(tm) Planar 2‐D Diode Array for High‐Dose‐Rate Brachytherapy Treatment Delivery Verifications
Authors: Macey N , Siebert M , Shvydka D , Parsai E 
Published: June 2015

Purpose:Despite improvements of HDR brachytherapy delivery systems, verification of source position is still typically based on the length of the wire reeled out relative to the parked position. Yet, the majority of errors leading to medical events in HDR treatments continue to be classified as missed targets or wrong treatment sites. We investigate the feasibility of using dose maps acquired with a two‐dimensional diode array to independently verify the source locations, dwell times, and dose during an HDR treatment.Methods:Custom correction factors were integrated into frame‐by‐frame raw counts recorded for a Varian VariSource™ HDR afterloader Ir‐192 source located at various distances in air and in solid water from a MapCHECK2™ diode array. The resultant corrected counts were analyzed to determine the dwell position locations and doses delivered. The local maxima of polynomial equations fitted to the extracted dwell dose profiles provided the X and Y coordinates while the distance to the source was determined from evaluation of the full width at half maximum (FWHM). To verify the approach, the experiment was repeated as the source was moved through dwell positions at various distances along an inclined plane, mimicking a vaginal cylinder treatment.Results:Dose map analysis was utilized to provide the coordinates of the source and dose delivered over each dwell position. The accuracy in determining source dwell positions was found to be +/−1.0 mm of the preset values, and doses within +/−3% of those calculated by the BrachyVision™ treatment planning system for all measured distances.Conclusion:Frame‐by‐frame data furnished by a 2 ‐D diode array can be used to verify the dwell positions and doses delivered by the HDR source over the course of treatment. Our studies have verified that measurements provided by the MapCHECK2™ can be used as a routine QA tool for HDR treatment delivery verification.
SU‐E‐T‐382: Evaluation of Clinical Application and Dosimetric Comparison for Treatment Plans of Gamma Knife and CyberKnife for Arteriovenous Malformations
Authors: Kuo C 
Published: June 2015

Purpose:To analyze and compare the characteristics of dose distributions between Gamma Knife (GK) and CyberKnife (CK), in treating arteriovenous malformations (AVMs), and evaluate the influences on their clinical applications.Methods:Twenty four patients with AVMs treated with CK of prescribed dose (PD) of 16–25 Gy in single fraction were selected. Each patient's CT images used for CK treatment planning with contours of targets and critical organs were exported and then loaded into the GK planning system. GK treatment plan with the same PD used in CK was generated for each patient. The metrics for dose comparison between GK and CK included conformity index (CI), gradient index (GI) of 75%, 50% and 25% of the PD, heterogeneity index (HI), volume of brain tissues covered by 10 Gy and 12 Gy, maximum dose to brainstem and beam‐on time. Paired Samples t‐test was used to analyze these metrics for significance (p value).Results:The CI were 0.744 ± 0.075 (GK) and 0.768 ± 0.086 (CK), p = 0.281. The GI75%, GI50%, and GI25% in GK and CK were 1.735 ± 0.100 and 2.439 ± 0.338 (p < 0.001), 3.169 ± 0.265 and 4.972 ± 0.852 (p < 0.001), and 8.650 ± 0.914 and 14.261 ± 2.476 (p < 0.001). The HI were 0.728 ± 0.072 (GK) and 0.313 ± 0.069 (CK), p < 0.001. There were significant differences both for volume of brain tissues covered by 10 Gy and 12 Gy in GK and CK (p < 0.001). GK had smaller maximum dose to brainstem. CK had shorter beam‐on time.Conclusion:GK has similar dose conformity as CK, and has better normal tissue sparing but is less efficient than CK.
SU‐E‐T‐388: Evaluation of Electronic Brachytherapy Dose Distributions in Tissue Equivalent Materials
Authors: Johnson M , Ahmad S , Johnson D 
Published: June 2015

Purpose:To study the measured and calculated dose distributions for electronic brachytherapy (EBT) in various tissue equivalent homogenous materials.Methods:Calculated dose distributions in water were generated using published TG‐43 parameters in Varian BrachyVision software for a 50 kVp, 50 cm Xoft source. Dose distributions were measured within a 3D‐scanning tank using dosimeters including: PTW 0.125 cc, pin‐point, and parallel‐plate ion chambers, Sun Nuclear “Edge” diode and Gafchromic EBT3 film. Multi‐channel film dosimetry was used in film analysis. EBT3 film curves were calibrated via radial dose comparison to both independently measured and published data. The resulting film calibration was utilized to measure dose distributions created by titanium filtered source utilized in clinical brachytherapy applications. Data was collected within homogenous PMMA, vinyl, polystyrene, paraffin, and water‐equivalent plastic phantoms.Results:Ion‐chamber data was corrected to effective points of measurement and normalized prior to comparison between calculated and measured dose distributions. Measurements made in water and water equivalent materials compared well with results from treatment planning software. The maximum percent differences (relative to water) observed between 1 cm and 3.5 cm depth from source for each of the phantom materials are as follows: PMMA 35%, polystyrene 41%, plastic‐water 23%, vinyl 115%, and paraffin 46%.Conclusion:The increased probability of photoelectric interactions occurring within the patient during electronic brachytherapy will emphasize the radiological differences between varying human tissues in dose deposition. These differences can Result in clinically significant dose perturbations and it is therefore recommended to move to a model based dose calculation, as outlined in TG‐186, to improve the dosimetric accuracy of low energy EBT.
SU‐E‐T‐390: Evaluation of Heterogeneity Corrections Made by RayStation Treatment Planning
Authors: Rodriguez M , Bartolac S , Rezaee M , Bissonnette J 
Published: June 2015

Purpose:To examine the agreement between absorbed doses calculated by RayStation treatment planning algorithm to those measured with gafchromic film and ion chamber when the photon beam is perturbed by attenuation or lateral scatter of lung material.Methods:A gafchromic EBT2 film was placed in the center of a 30×30×20 cm3 solid water phantom with a 5 cm lung slab placed at 10 cm depth. The film was irradiated at SSD = 100 cm with a 6 MV photon beam, 10×10 and 5×5 cm2 field sizes and with the beam parallel to the film and lung slab. A CT was performed to the phantom arrangement for RayStation dose calculation. The films were scanned in an Epson 10000X flatbed scanner and analyzed using the red channel, 16 bits, 76 dpi. PDD curves at the central axis and profiles at dmax were also measured in water using a CC13 (0.13 CC) ion chamber. Measurements and calculation of PDD curves at the central axis and profiles at dmax and 20 cm depth were compared using the criteria suggested by the AAPM Task Group # 53.Results:The PDD curves measured with gafchromic film and those measured in water with ion chamber agree with the ones calculated by RayStation within the uncertainty of the measurements which is within 3%. The passing rate values of the measured and calculated profiles for the 2 field sizes are within 94% for both at dmax and at 20 cm depth.Conclusion:Raystation dose calculation engine models inhomogeneity corrections. Differences between the calculated PDD curves and profiles and those measured with gafchromic film are within the uncertainty of the measurements and inside of the agreement tolerance suggested by TG53. Therefore, RayStation treatment planning has an acceptable algorithm to correct dose delivered by photon beams perturbed by lung tissue.
SU‐E‐T‐391: Evaluation of Image Parameters Impact On the CT Calibration Curve for Proton Therapy
Authors: Xiao Z , Reyhan M , Huang Q , Zhang M , Yue N , Chen T 
Published: June 2015

Purpose:The calibration of the Hounsfield units (HU) to relative proton stopping powers (RSP) is a crucial component in assuring the accurate delivery of proton therapy dose distributions to patients. The purpose of this work is to assess the uncertainty of CT calibration considering the impact of CT slice thickness, position of the plug within the phantom and phantom sizes.Methods:Stoichiometric calibration method was employed to develop the CT calibration curve. Gammex 467 tissue characterization phantom was scanned in Tomotherapy Cheese phantom and Gammex 451 phantom by using a GE CT scanner. Each plug was individually inserted into the same position of inner and outer ring of phantoms at each time, respectively. 1.25 mm and 2.5 mm slice thickness were used. Other parameters were same.Results:HU of selected human tissues were calculated based on fitted coefficient (Kph, Kcoh and KKN), and RSP were calculated according to the Bethe‐Bloch equation. The calibration curve was obtained by fitting cheese phantom data with 1.25 mm thickness. There is no significant difference if the slice thickness, phantom size, position of plug changed in soft tissue. For boney structure, RSP increases up to 1% if the phantom size and the position of plug changed but keep the slice thickness the same. However, if the slice thickness varied from the one in the calibration curve, 0.5%–3% deviation would be expected depending on the plug position. The Inner position shows the obvious deviation (averagely about 2.5%).Conclusion:RSP shows a clinical insignificant deviation in soft tissue region. Special attention may be required when using a different slice thickness from the calibration curve for boney structure. It is clinically practical to address 3% deviation due to different thickness in the definition of clinical margins.
SU‐E‐T‐392: Evaluation of Ion Chamber/film and Log File Based QA to Detect Delivery Errors
Authors: Nelson C , Ohrt J , Mason B , Kirsner S 
Published: June 2015

Purpose:Ion chamber and film (ICAF) is a method used to verify patient dose prior to treatment. More recently, log file based QA has been shown as an alternative for measurement based QA. In this study, we delivered VMAT plans with and without errors to determine if ICAF and/or log file based QA was able to detect the errors.Methods:Using two VMAT patients, the original treatment plan plus 7 additional plans with delivery errors introduced were generated and delivered. The erroneous plans had gantry, collimator, MLC, gantry and collimator, collimator and MLC, MLC and gantry, and gantry, collimator, and MLC errors. The gantry and collimator errors were off by 4⁰ for one of the two arcs. The MLC error introduced was one in which the opening aperture didn't move throughout the delivery of the field. For each delivery, an ICAF measurement was made as well as a dose comparison based upon log files. Passing criteria to evaluate the plans were ion chamber less and 5% and film 90% of pixels pass the 3mm/3% gamma analysis(GA). For log file analysis 90% of voxels pass the 3mm/3% 3D GA and beam parameters match what was in the plan.Results:Two original plans were delivered and passed both ICAF and log file base QA. Both ICAF and log file QA met the dosimetry criteria on 4 of the 12 erroneous cases analyzed (2 cases were not analyzed). For the log file analysis, all 12 erroneous plans alerted a mismatch in delivery versus what was planned. The 8 plans that didn't meet criteria all had MLC errors.Conclusion:Our study demonstrates that log file based pre‐treatment QA was able to detect small errors that may not be detected using an ICAF and both methods of were able to detect larger delivery errors.
SU‐E‐T‐396: Evaluation of Novel Open Face Intracranial Immobilization Devices
Authors: Wiant D , Maurer J , Liu H , Hayes L , Sintay B 
Published: June 2015

Purpose:Focal intracranial treatments, such as stereotactic radiosurgery, require that motion be minimized during treatment. This level of immobilization is typically achieved with custom thermoplastic masks that cover the patient's face. These masks they do not allow active monitoring of patient position during treatment, and in many cases they induce claustrophobia and anxiety. This work evaluates potential motion using a newly developed faceless mask system designed to reduce anxiety and allow intrafraction monitoring.Methods:Custom masks were created for five healthy volunteers using both the standard mask and the mask with integrated bite system (IBS). Each volunteer was monitored with surface imaging system for 15 minutes to evaluate physiological motion. They were then asked to move as much as possible to evaluate forced motion. The real time surface imaging information was recorded and analyzed off‐line.Results:The mean root‐mean‐square (RMS) of the linear displacements over the 15 minute monitoring periods ranged from 0.3 mm – 0.7 mm with the standard mask and 0.3 mm – 0.5 mm for the mask with IBS. The maximum individual variance was 0.4 mm (2 standard deviations) both with and without IBS. The maximum RMS displacement during forced movements was 9.2 mm without IBS and 4.9 mm with IBS. The mean RMS difference in position before and after forced motion over all patients and movements (with and without IBS) was 0.5 mm +/−0.5 mm (2 SD), i.e. the volunteers were returning to within 0.5 mm of their initial position after forced movements.Conclusion:The intracranial mask system is able to provide sub‐millimeter immobilization for resting volunteers, and the system can limit motion to < 5 mm under the adverse conditions, providing adequate immobilization for any type of intracranial treatment while potentially improving patient comfort and reducing anxiety and claustrophobic episodesThis work was partially supported by Qfix.
SU‐E‐T‐397: Evaluation of Planned Dose Distributions by Monte Carlo (0.5%) and Ray Tracing Algorithm for the Spinal Tumors with CyberKnife
Authors: Cho H , Hepel J , Brindle J 
Published: June 2015

Purpose:To analyze and evaluate dose distribution between Ray Tracing (RT) and Monte Carlo (MC) algorithms of 0.5% uncertainty on a critical structure of spinal cord and gross target volume and planning target volume.Methods:Twenty four spinal tumor patients were treated with stereotactic body radiotherapy (SBRT) by CyberKnife in 2013 and 2014. The MC algorithm with 0.5% of uncertainty is used to recalculate the dose distribution for the treatment plan of the patients using the same beams, beam directions, and monitor units (MUs).Results:The prescription doses are uniformly larger for MC plans than RT except one case. Up to a factor of 1.19 for 0.25cc threshold volume and 1.14 for 1.2cc threshold volume of dose differences are observed for the spinal cord.Conclusion:The MC recalculated dose distributions are larger than the original MC calculations for the spinal tumor cases. Based on the accuracy of the MC calculations, more radiation dose might be delivered to the tumor targets and spinal cords with the increase prescription dose.
SU‐E‐T‐398: Evaluation of Radiobiological Parameters Using Serial Tumor Imaging During Radiotherapy as An Inverse Ill‐Posed Problem
Authors: Chvetsov A , Sandison G , Schwartz J , Rengan R 
Published: June 2015

Purpose:Combination of serial tumor imaging with radiobiological modeling can provide more accurate information on the nature of treatment response and what underlies resistance. The purpose of this article is to improve the algorithms related to imaging‐based radiobilogical modeling of tumor response.Methods:Serial imaging of tumor response to radiation therapy represents a sum of tumor cell sensitivity, tumor growth rates, and the rate of cell loss which are not separated explicitly. Accurate treatment response assessment would require separation of these radiobiological determinants of treatment response because they define tumor control probability. We show that the problem of reconstruction of radiobiological parameters from serial imaging data can be considered as inverse ill‐posed problem described by the Fredholm integral equation of the first kind because it is governed by a sum of several exponential processes. Therefore, the parameter reconstruction can be solved using regularization methods.Results:To study the reconstruction problem, we used a set of serial CT imaging data for the head and neck cancer and a two‐level cell population model of tumor response which separates the entire tumor cell population in two subpopulations of viable and lethally damage cells. The reconstruction was done using a least squared objective function and a simulated annealing algorithm. Using in vitro data for radiobiological parameters as reference data, we shown that the reconstructed values of cell surviving fractions and potential doubling time exhibit non‐physical fluctuations if no stabilization algorithms are applied. The variational regularization allowed us to obtain statistical distribution for cell surviving fractions and cell number doubling times comparable to in vitro data.Conclusion:Our results indicate that using variational regularization can increase the number of free parameters in the model and open the way to development of more advanced algorithms which take into account tumor heterogeneity, for example, related to hypoxia.
SU‐E‐T‐407: Evaluation of the Stopping Power and Imaging Visibility for Iodine Based Contrast in Proton Therapy
Authors: Singh H , Zhao L , Rana S , Chacko M , Zheng Y 
Published: June 2015

Purpose:The purpose of this study was to investigate the difference between calculated and measured relative linear stopping power (RLSP) for contrast medium in proton therapy. Furthermore, the visibility for different concentrations in prostate phantom on orthogonal X‐ray system was evaluatedMethods and Materials:In prostate cancer patient, rectal balloon along with the contrast media was used to visualize the balloon position, thus facilitating the patient setup during each fraction of the uniform scanning proton treatment. There were no fiducial markers implanted in the prostate for this patient. A blue wax phantom with outer dimensions 10cm(H) × 14.5cm(L) × 10cm(W) was made in house. To hold iodine based contrast solution, a rectangular shaped hole with dimensions 7cm(H) × 8cm(L) × 4cm(W) was made inside the phantom. Organically bound 8.5% iodine based Cystografin Dilute contrast agent with molecular formula C11H9I3N2O4.C7H17NO5 was used in this study. Six solutions were prepared; each mixture of water and iodine based contrast agent at different concentrations as 0%, 5%, 10%, 20%, 30% and 50%. During computed tomographic(CT) simulation, solutions were placed together at the isocenter of CT and scanned at 120kVp using the same protocol as for prostate cancer patients. The treatment planning was done in CMS‐XiO system. Multi‐layer‐ion‐chamber (MLIC) was used to measure residual proton range.Results:The 50% concentration contrast solution was used during treatment for better visualization on orthogonal X‐ray image. The measured RLSP for 5%, 10%, 20%, 30% & 50% solutions were 1.005, 1.010, 1.018, 1.023 & 1.033; and similarly calculated RLSP from XiO were 1.090, 1.135, 1.222, 1.299 & 1.448 respectively.Conclusion:The treatment planning system could overestimates the relative stopping power of contrast solution with high concentrations. It is recommended to override the contrast with measured RLSP for high atomic number based contrast solution in treatment planning for proton therapy.
SU‐E‐T‐411: Evaluation of Treatment Plan Quality Between Two Treatment Planning Systems for VMAT
Authors: Yang T , Xu W , Ge R , Qu B , Xu S 
Published: June 2015

Purpose:To investigate the treatment plan quality between two treatment planning systems (TPS) for volumetric modulated Arc therapy (VMAT).Methods:VMAT plans based on Varian Eclipse (Ver10.0) and Philips Pinnacle (Ver9.10) TPS were respectively generated by 10 cervical cancer patients by using 2, 3 arcs, controlling the gantry movement with the space of 2 degrees and setting the same optimization constraint as soon as possible. The delivery system with VMAT was Varian Clinac iX machine. The prescription dose was 50Gy/23f for regions at high risk (PTV1), and 45Gy/23f for regions at low risk (PTV). The difference of treatment plans was evaluated by dose distribution and delivery efficiency.Results:The VMAT 2‐arcs plans based on Pinnacle in the conformal indexes of PTV(CI: 0.77±0.05 vs 0.75±0.02, p>0.05), and OARs (such as V30, V40 of rectum and bladder) showed slightly better than those of Eclipse TPS, and the homogeneity indexes (HI) of in Pinnacle were slightly worse than the Eclipse (PTV: 0.17±0.01 vs 0.14±0.01, p <0.05; PTV1: 0.06±0.01 vs 0.04±0.002, p <0.05), there were statistical difference. The MUs with 2‐arcs (750±91 vs 1118±84, p <0.05) and 3‐arcs (837±86 vs 1215±208, p <0.05) of the Eclipse plans had a clear advantages over the Pinnacle ones, with the statistical difference. The 3‐arc plans in Eclipse showed an advantage over the 2‐arcs ones and the plan quality of 3‐arcs in Pinnacle had no advantage comparing with 2 arcs, but the MUs of 3 Arcs in both Eclipse (837±86 vs 750±92, p <0.05) and Pinnacle (1215±208 vs 1118±84, p >0.05) were more than those of 2‐arcs.Conclusion:For patients with cervical cancer, the VMAT treatment plans of two TPSs could achieve clinical acceptable dose distribution. However, we will still need more cases to further study and determine the optimization and performance characteristics of the two commercial TPSs.
SU‐E‐T‐413: Examining Acquisition Rate for Using MatriXX Ion Chamber Array to Measure HDR Brachytherapy Treatments
Authors: Wagar M , Bhagwat M , O'Farrell D , Friesen S , Buzurovic I , Damato A , Devlin P , Cormack R 
Published: June 2015

Purpose:There are unique obstacles to implementing the MatriXX ionchamber array as a QA tool in Brachytherapy given that the device is designed for use in the MV energy range. One of the challenges we investigate is the affect of acquisition rates on dose measurement accuracy for HDR treatment plans.Methods:A treatment plan was optimized in Oncentra Brachy TPS to deliver a planar dose to a 5×5cm region at 10mm depth. The applicator was affixed to the surface of the MatriXX array. The plan was delivered multiple times using a Nucleatron HDR afterloader with a 2.9Ci Ir192 source. For each measurement the sampling rate of the MatriXX movie mode was varied (30ms and 500ms). This experiment was repeated with identical parameters, following a source exchange, with an 11.2Ci Ir192 source. Finally, a single snap measurement was acquired. Analysis was preformed to evaluate the fidelity of the dose delivery for each iteration of the experiment. Evaluation was based on the comparison between the measured and TPS predicted dose.Results:Higher sample rates induce a greater discrepancy between the predicted and measured dose. Delivering the plan using a lower activity source also produced greater discrepancy in the measurement due to the increased delivery time. Analyzing the single snap measurement showed little difference from the 500ms integral dose measurement.Conclusion:The advantage of using movie mode for HDR treatment delivery QA is the ability for real time source tracking in addition to dose measurement. Our analysis indicates that 500ms is an optimal frame rate.