bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐479: IMRT Plan Recalculation in Patient Based On Dynalog Data and the Effect of a Single Failing MLC Motor
Authors: Morcos M , Mitrou E 
Published: June 2015

Purpose:Using Linac dynamic logs (Dynalogs) we evaluate the impact of a single failing MLC motor on the deliverability of an IMRT plan by assessing the recalculated dose volume histograms (DVHs) taking the delivered MLC positions and beam hold‐offs into consideration.Methods:This is a retrospective study based on a deteriorating MLC motor (leaf 36B) which was observed to be failing via Dynalog analysis. To investigate further, Eclipse‐importable MLC files were generated from Dynalogs to recalculate the actual delivered dose and to assess the clinical impact through DVHs. All deliveries were performed on a Varian 21EX linear accelerator equipped with Millennium‐120 MLC. The analysis of Dynalog files and subsequent conversion to Eclipse‐importable MLC files were all performed by in‐house programming in Python. Effects on plan DVH are presented in the following section on a particular brain‐IMRT plan which was delivered with a failing MLC motor which was then replaced.Results:Global max dose increased by 13.5%, max dose to the brainstem PRV increased by 8.2%, max dose to the optic chiasm increased by 7.6%, max dose to optic nerve increased by 8.8% and the mean dose to the PTV increased by 7.9% when comparing the original plan to the fraction with the failing MLC motor. The reason the dose increased was due to the failure being on the B‐bank which is the lagging side on a sliding window delivery, therefore any failures on this side will cause an over‐irradiation as the B‐bank leaves struggles to keep the window from growing.Conclusion:Our findings suggest that a single failing MLC motor may jeopardize the entire delivery. This may be due to the bad MLC motor drawing too much current causing all MLCs on the same bank to underperform. This hypothesis will be investigated in a future study.
SU‐E‐T‐483: In Vivo Dosimetry of Conventional and Rotational Intensity Modulated Radiotherapy Using Integral Quality Monitor (IQM)
Authors: Lin L , Qian J , Gonzales R , Keck J , Armour E , Wong J 
Published: June 2015

Purpose:To investigate the accuracy, sensitivity and constancy of integral quality monitor (IQM), a new system for in vivo dosimetry of conventional intensity modulated radiation therapy (IMRT) or rotational volumetric modulated arc therapy (VMAT)Methods:A beta‐version IQM system was commissioned on an Elekta Infinity LINAC equipped with 160‐MLCs Agility head. The stationary and rotational dosimetric constancy of IQM was evaluated, using five‐field IMRT and single‐or double‐arc VMAT plans for prostate and head‐and‐neck (H&N) patients. The plans were delivered three times over three days to assess the constancy of IQM response. Picket fence (PF) fields were used to evaluate the sensitivity of detecting MLC leaf errors. A single leaf offset was intentionally introduced during delivery of various PF fields with segment apertures of 3×1, 5×1, 10×1, and 24×1cm2. Both 2mm and 5mm decrease in the field width were used.Results:Repeated IQM measurements of prostate and H&N IMRT deliveries showed 0.4 and 0.5% average standard deviation (SD) for segment‐by‐segment comparison and 0.1 and 0.2% for cumulative comparison. The corresponding SDs for VMAT deliveries were 6.5, 9.4% and 0.7, 1.3%, respectively. Statistical analysis indicates that the dosimetric differences detected by IQM were significant (p < 0.05) in all PF test deliveries. The largest average IQM signal response of a 2 mm leaf error was found to be 2.1% and 5.1% by a 5mm leaf error for 3×1 cm2 field size. The same error in 24×1 cm2 generates a 0.7% and 1.4% difference in the signal.Conclusion:IQM provides an effective means for real‐time dosimetric verification of IMRT/ VMAT treatment delivery. For VMAT delivery, the cumulative dosimetry of IQM needs to be used in clinical practice.
SU‐E‐T‐484: In Vivo Dosimetry Tolerances in External Beam Fast Neutron Therapy
Authors: Young L , Gopan O 
Published: June 2015

Purpose:Optical stimulated luminescence (OSL) dosimetry with Landauer Al2O3:C nanodots was developed at our institution as a passive in vivo dosimetry (IVD) system for patients treated with fast neutron therapy. The purpose of this study was to establish clinically relevant tolerance limits for detecting treatment errors requiring further investigation.Methods:Tolerance levels were estimated by conducting a series of IVD expected dose calculations for square field sizes ranging between 2.8 and 28.8 cm. For each field size evaluated, doses were calculated for open and internal wedged fields with angles of 30°, 45°, or 60°. Theoretical errors were computed for variations of incorrect beam configurations. Dose errors, defined as the percent difference from the expected dose calculation, were measured with groups of three nanodots placed in a 30 × 30 cm solid water phantom, at beam isocenter (150 cm SAD, 1.7 cm Dmax). The tolerances were applied to IVD patient measurements.Results:The overall accuracy of the nanodot measurements is 2–3% for open fields. Measurement errors agreed with calculated errors to within 3%. Theoretical estimates of dosimetric errors showed that IVD measurements with OSL nanodots will detect the absence of an internal wedge or a wrong wedge angle. Incorrect nanodot placement on a wedged field is more likely to be caught if the offset is in the direction of the “toe” of the wedge where the dose difference in percentage is about 12%. Errors caused by an incorrect flattening filter size produced a 2% measurement error that is not detectable by IVD measurement alone.Conclusion:IVD with nanodots will detect treatment errors associated with the incorrect implementation of the internal wedge. The results of this study will streamline the physicists’ investigations in determining the root cause of an IVD reading that is out of normally accepted tolerances.
SU‐E‐T‐486: In Vivo Skin Dosimetry Using the Exradin W1 Plastic Scintillation Detector for Passively Scattered Proton Beam Therapy
Authors: Alsanea F , Wootton L , Kudchadker R , Usama M , Beddar S 
Published: June 2015

Purpose:To evaluate the accuracy and usefulness of plastic scintillation detectors used for skin dosimetry of patients undergoing passive scatter proton therapy.Methods:Following an IRB approved protocol, six patients undergoing passively scattered proton beam therapy for prostate cancer were selected for in vivo skin dosimetry using the Exradin W1 plastic scintillator. The detector was calibrated on a Cobalt‐60 unit, and phantom measurements in the proton beam with the W1 and a calibrated parallel plate ion chamber were used to account for the under‐response due to high LET at energies used for treatment. Measurements made in a heated water tank were used to account for temperature dependence. For in vivo measurements, the W1 is fixed to the patient's skin with medical tape in the center of each of two laterally opposed treatment fields. Measurements will be performed once per week for each patient for the duration of treatment, for a total of thirty six measurements. The measured dose will be compared to the expected dose, extracted from the Eclipse treatment planning system. The average difference over all measurements and per‐patient will be computed, as well as standard deviations.Results:The calibrated detector exhibited a 7% under‐response in 225 and 250 MeV beams, and a 4% under‐response when used at 37 °C (relative to the response at the calibration temperature of 20 °C). Patient measurements are ongoing.Conclusion:The Exradin W1 plastic scintillator detector is a strong candidate for in vivo skin dosimetry in passively scattered proton beams as PSDs are water equivalent and very small (2mm in diameter), permitting accurate measurements that do not perturb the delivered dose.This project was supported in part by award number CA182450 from the National Cancer Institute.
SU‐E‐T‐490: Independent Three‐Dimensional (3D) Dose Verification of VMAT/SBRT Using EPID and Cloud Computing
Authors: Ding A , Han B , Bush K , Wang L , Xing L 
Published: June 2015

Purpose:Dosimetric verification of VMAT/SBRT is currently performed on one or two planes in a phantom with either film or array detectors. A robust and easy‐to‐use 3D dosimetric tool has been sought since the advent of conformal radiation therapy. Here we present such a strategy for independent 3D VMAT/SBRT plan verification system by a combined use of EPID and cloud‐based Monte Carlo (MC) dose calculation.Methods:The 3D dosimetric verification proceeds in two steps. First, the plan was delivered with a high resolution portable EPID mounted on the gantry, and the EPID‐captured gantry‐angle‐resolved VMAT/SBRT field images were converted into fluence by using the EPID pixel response function derived from MC simulations. The fluence was resampled and used as the input for an in‐house developed Amazon cloud‐based MC software to reconstruct the 3D dose distribution. The accuracy of the developed 3D dosimetric tool was assessed using a Delta4 phantom with various field sizes (square, circular, rectangular, and irregular MLC fields) and different patient cases. The method was applied to validate VMAT/SBRT plans using WFF and FFF photon beams (Varian TrueBeam STX).Results:It was found that the proposed method yielded results consistent with the Delta4 measurements. For points on the two detector planes, a good agreement within 1.5% were found for all the testing fields. Patient VMAT/SBRT plan studies revealed similar level of accuracy: an average γ‐index passing rate of 99.2± 0.6% (3mm/3%), 97.4± 2.4% (2mm/2%), and 72.6± 8.4 % ( 1mm/1%).Conclusion:A valuable 3D dosimetric verification strategy has been developed for VMAT/SBRT plan validation. The technique provides a viable solution for a number of intractable dosimetry problems, such as small fields and plans with high dose gradient.
SU‐E‐T‐491: Influence of Applicator Dimensions On Doses to Bladder, Rectum and Sigmoid in HDR Brachytherapy for Cervical Cancer
Authors: Dumane V , Rhome R , Yuan Y , Gupta V 
Published: June 2015

Purpose:To study the influence of dimensions of the tandem and ring applicator on bladder D2cc, rectum D2cc and sigmoid D2cc in HDR treatment planning for cervical cancer.Methods:53 plans from 13 patients treated at our institution with the tandem and ring applicator were retrospectively reviewed. Prescription doses were one of the following: 8 Gy × 3, 7 Gy × 4 and 5.5 Gy × 5. Doses to the D2ccs of the bladder, rectum and the sigmoid were recorded. These doses were normalized to their relative prescriptions doses. Correlations between the normalized bladder D2cc, rectum D2cc and sigmoid D2cc were investigated and linear regression models were developed to study the dependence of these doses on the ring diameter and the applicator angle.Results:Normalized doses to the D2cc of the bladder, rectum and sigmoid showed statistically significant correlation (P < 0.05) to the applicator angle. Significant correlation was also noted for the normalized D2cc of the rectum and the sigmoid with the ring diameter. The normalized bladder D2cc was found to decrease with applicator angle on an average by 22.65% ± 4.43% while the same for the rectum and sigmoid were found to increase on an average by 14.43% ± 1.65% and 14.01% ± 1.42% respectively. Both the rectum and sigmoid D2cc reduced with increasing ring diameter by 12.93% ± 1.95% and 11.27% ± 1.79%. No correlation was observed between the normalized bladder D2cc and the ring diameter.Conclusion:Preliminary regression models developed in this study can potentially aid in the choice of the appropriate applicator angle and ring diameter for tandem and ring implant so as to optimize doses to the bladder, rectum and sigmoid.
SU‐E‐T‐498: Initial Characterization of the New EBT XD Gafchromic Film
Authors: Grams M , Gustafson J , Long K , de los Santos L Fong 
Published: June 2015

PurposeTo assess the dosimetric accuracy of the new EBT XD (eXtended Dose) Gafchromic film and to compare the lateral scan effect between EBT XD and EBT3 film.Methods:All films were exposed in solid water using a 6 MV beam and were analyzed with FilmQA Pro software and an Epson 10000 XL scanner. Calibration was performed using films exposed to 8 known doses from 0–3000 cGy. To assess dosimetric accuracy, a 15×18 cm2 60° EDW delivered a dose range of 200–2900 cGy to 4 separate EBT XD films. Comparison to treatment planning system (TPS) predictions was made using a gamma analysis with 2%/2mm passing criteria. To assess the lateral scan effect, 21 × 21 cm2 open fields delivered doses of 1000, 2000, and 3000 cGy isocentrically to both EBT3 and EBT XD films at 10 cm depth. Films were centered and scanned such that the widest parts of the exposed film extended lateral to the center of the scanner bed in order to maximize the lateral scan effect. Ratios of measured to TPS predicted doses for EBT3 and EBT XD film were calculated at 5 cm and 8 cm lateral from the center of the scanner bed to quantitatively assess the lateral scan effect.ResultsThe average gamma passing rate for the EDW was 98.9% (range 98.7 – 99.1%). EBT XD film exhibited minimal lateral scan effect (<1%) up to 30 Gy. In contrast, EBT3 showed an under‐response of 13% and 25% at lateral positions of 5 cm and 8 cm respectively for the 30 Gy exposure.ConclusionEBT XD can accurately measure dose over a wide dynamic range. The non‐polarizing structure of its active ingredient essentially eliminates the lateral scan effect up to at least 30 Gy. EBT XD film is therefore well suited for SRS/SBRT verification measurements.
SU‐E‐T‐503: Intensity Modulated Proton Therapy (IMPT) Versus Intensity Modulated X‐Ray Therapy (IMRT) for Patient with Hepatocellular Carcinoma: A Dosimetric Comparison
Authors: Singh H , Zhao L , Prabhu K , Rana S , Zheng Y 
Published: June 2015

PurposeThis study compares the dosimetric parameters in treatment of unresectable hepatocellular carcinoma between intensity modulated proton therapy (IMPT) and intensity modulated x‐ray radiation therapy (IMRT). Methods and Materials: We studied four patients treated at our institution. All patients were simulated supine with 4D‐CT using a GE light speed simulator with a maximum slice thickness of 3mm. The average CT and an internal target volume to account for respiration motion were used for planning. Both IMRT and IMPT plans were created using Elekta's CMSXiO treatment planning system (TPS). The prescription dose was 58.05 CGE in 15 fractions. The IMRT plans had five beams with combination of co‐planar and non‐co‐planar. The IMPT plans had 2 to 3 beams. Dose comparison was performed based on the averaged results of the four patients.ResultsThe mean dose and V95% to PTV were 58.24CGE, 98.57% for IMPT, versus 57.34CGE and 96.68% for IMRT, respectively. The V10, V20, V30 and mean dose of the normal liver for IMPT were 23.10%, 18.61%, 13.75% and 9.78 CGE; and 47.19%, 37.55%, 22.73% and 17.12CGE for IMRT. The spinal cord didn't receive any dose in IMPT technique, but received a maximum of 18.77CGE for IMRT. The IMPT gave lower maximum dose to the stomach as compared to IMRT (19.26 vs 26.35CGE). V14 for left and right kidney was 0% and 2.32% for IMPT and 3.89% and 29.54% for IMRT. The mean dose, V35, V40 and V45 for small bowl were similar in both techniques, 0.74CGE, 6.27cc, 4.85cc and 3.53 cc for IMPT, 3.47CGE, 9.73cc, 7.61cc 5.35cc for IMRT.ConclusionBased on this study, IMPT plans gave less dose to the critical structures such as normal liver, kidney, stomach and spinal cord as compared to IMRT plans, potentially leading to less toxicity and providing better quality of life for patients.
SU‐E‐T‐511: Inter‐Rater Variability in Classification of Incidents in a New Incident Reporting System
Authors: Pappas D , Reis S , Ali A , Kapur A 
Published: June 2015

PurposeTo determine how consistent the results of different raters are when reviewing the same cases within the Radiation Oncology Incident Learning System (ROILS).MethodsThree second‐year medical physics graduate students filled out incident reports in spreadsheets set up to mimic ROILS. All students studied the same 33 cases and independently entered their assessments, for a total of 99 reviewed cases. The narratives for these cases were obtained from a published International Commission on Radiological Protection (ICRP) report which included shorter narratives selected from the Radiation Oncology Safety Information System (ROSIS) database. Each category of questions was reviewed to see how consistent the results were by utilizing free‐marginal multirater kappa analysis. The percentage of cases where all raters shared full agreement or full disagreement was recorded to show which questions were answered consistently by multiple raters for a given case. The consistency among the raters was analyzed between ICRP and ROSIS cases to see if either group led to more reliable results.ResultsThe categories where all raters agreed 100 percent in their choices were the event type (93.94 percent of cases 0.946 kappa) and the likelihood of the event being harmful to the patient (42.42 percent of cases 0.409 kappa). The categories where all raters disagreed 100 percent in their choices were the dosimetric severity scale (39.39 percent of cases 0.139 kappa) and the potential future toxicity (48.48 percent of cases 0.205 kappa). ROSIS had more cases where all raters disagreed than ICRP (23.06 percent of cases compared to 15.58 percent, respectively).ConclusionDespite reviewing the same cases, the results among the three raters was widespread. ROSIS narratives were shorter than ICRP, which suggests that longer narratives lead to more consistent results. This study shows that the incident reporting system can be optimized to yield more consistent results.
SU‐E‐T‐512: Intrinsic Characteristics of the Nine Detectors and Evaluation of Their Performance in Non‐Equilibrium Radiation Dosimetry
Authors: Markovic M , Stathakis S , Jurkovic I , Mavroidis P , Papanikolaou N 
Published: June 2015

PurposeThe aim for the study was to compare intrinsic characteristics of the nine detectors and evaluate their performance in non‐equilibrium radiation dosimetry.MethodsThe intrinsic characteristics of the nine detectors that were evaluated are based on the composition and size of the active volume, operating voltage, initial recombination of the collected charge, temperature, the effective cross section of the detectors. The shortterm stability and collection efficiency has been investigated. The minimum radiation detection sensitivity and detectors leakage current has been measured. The sensitivity to changes in energy spectrum as well as change in incident beam angles were measured an analyzed.ResultsThe short‐term stability of the measurements within every detector showed consistency in the measured values with the highest value of the standard deviation of the mean not exceeding 0.5%. Air ion chamber detectors showed minimum sensitivity to change in incident beam angles while diode detectors underestimated measurements up to 16%. Comparing the slope of the tangents for detector's sensitivity curve, diode detectors illustrate more sensitivity to change in photon spectrum than ion chamber detectors. The change in radiation detection sensitivity with increase in dose delivered has been observed for semiconductor detectors with maximum deviation 0.01% for doses between 1 Gy and 10 Gy. Leakage current has been mainly influenced by bias voltage (ion chamber detectors) and room light intensity (diode detectors). With dose per pulse varying from 1.47E−4 to 5.1E−4 Gy/pulse the maximum change in collection efficiency was 1.4% for the air ion chambers up to 8% for liquid filled ion chamber.ConclusionBroad range of measurements performed showed all the detectors susceptible to some limitations and while they are suitable for use in broad scope of applications, careful selection has to be made for particular range of measurements.
SU‐E‐T‐514: Investigating the Dose Distributions of Equiangular Spaced Noncoplanar Beams
Authors: Mitchell T , Maxim P , Hadsell M , Loo B 
Published: June 2015

PurposeIt has been demonstrated that the use of noncoplanar beams in radiation therapy may Result in dose distributions that are comparable or better than standard coplanar beams [Pugachev, 2001]. A radiation therapy system designed with a noncoplanar beam geometry could allow for a full ring diagnostic quality imaging system to be placed around the patient. Additionally, if the noncoplanar beams were fixed in number and in their angle with respect to the patient's axial plane, then both treatment and imaging could be achieved concurrently without the need for moving parts, which could greatly reduce treatment times. For such a system to be designed, it is necessary to determine the appropriate number of beams and the beam angles to achieve optimal dose distributions. For simplicity, the beam angles are assumed to be equiangular in the patient's axial plane, and only the beam angle with respect to the axial plane are varied. This study aims to investigate the dose distributions produced by equiangular noncoplanar beams for multiple beam numbers and beam angles, and to compare these dose distributions with distributions achieved in coplanar volumetric arc therapy (VMAT).MethodsDose distributions produced by noncoplanar beams were calculated using the Varian Eclipse treatment planning system by varying the gantry, collimator, and couch angles to simulate the noncoplanar delivery method. Noncoplanar intensity‐modulated (NC‐IMRT) beams using 8, 12, and 16 beams with angles varying from 45 degrees to 54 with respect to the patient's axial plane were studied.ResultsThe NC‐IMRT beams produced dose distributions comparable to VMAT plans for a number of treatment sites, and were capable of meeting similar dose‐volume histogram constraints.ConclusionThis study has demonstrated that a noncoplanar beam delivery method with fixed beam numbers and beam angles is capable of delivering dose distributions comparable to VMAT plans currently in use.
SU‐E‐T‐515: Investigating the Linear Energy Transfer Dependency of Different PRESAGE Formulations in a Proton Beam
Authors: Carroll M , Alqathami M , Blencowe A , Ibbott G 
Published: June 2015

PurposePrevious studies have reported an under‐response of PRESAGE in a proton beam as a Result of the extremely high LET in the distal end of the spread out Bragg peak (SOBP). This work is a preliminary investigation to quantify the effect of the formulation, specifically the concentration of halocarbon radical initiator relative to leuco dye, on radical recombination resulting in LET dependence.MethodsThe traditional PRESAGE formulation developed by Heuris Pharma was altered to constitute radical initiator concentrations of 5, 15, and 30% (low, medium, and high) by weight with all other components balanced to maintain proportionality. Chloroform was specifically examined in this study and all dosimeters were made in‐house. Cylindrical PRESAGE dosimeters (3.5cm diameter and 6cm length) were made for each formulation and irradiated by a 200‐MeV proton beam to 500 cGy across a 2cm SOBP. Dosimeters were read out using the DMOS optical‐CT scanner. The dose distributions were analyzed and dose profiles were used to compare the relative dose response to find the stability across the high‐LET region of the SOBP. LET dependence was measured by the variation to ion chamber measurements for the final 25% of the SOBP (∼0.5cm) prior to the distal‐90 of each profile.ResultsRelative to ion chamber data, all PRESAGE dosimeters showed an under‐response at the distal end of the SOBP. The medium concentration formulation matched most closely with an average 8.3% under‐response closely followed by the low concentration at 12.2% and then the high concentration at 22.8%. In all three cases, the highest points of discrepancy were in the distal most regions.ConclusionThe radical initiator concentration in PRESAGE can be tailored to reduce the LET dependence in a proton beam. This warrants further study to quantify comprehensively the effect of concentration of different halocarbon radical initiators on LET dependency.Grant number 5RO1CA100835