bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐155: Validation of a Commercial Monte Carlo Dose Calculation Algorithm for Proton Therapy
Authors: Saini J , St. James S , Traneus E , Wong T , Stewart R , Bloch C
Published: July 2016

Purpose:

Compare proton pencil beam scanning dose measurements to GATE/GEANT4 (GMC) and RayStation™ Monte Carlo (RMC) simulations.

Methods:

Proton pencil beam models of the IBA gantry at the Seattle Proton Therapy Center were developed in the GMC code system and a research build of the RMC. For RMC, a preliminary beam model that does not account for upstream halo was used. Depth dose and lateral profiles are compared for the RMC, GMC and a RayStation™ pencil beam dose (RPB) model for three spread out Bragg peaks (SOBPs) in homogenous water phantom. SOBP comparisons were also made among the three models for a phantom with a (i) 2 cm bone and a (ii) 0.5 cm titanium insert.

Results:

Measurements and GMC estimates of R80 range agree to within 1 mm, and the mean point‐to‐point dose difference is within 1.2% for all integrated depth dose (IDD) profiles. The dose differences at the peak are 1 to 2%. All of the simulated spot sigmas are within 0.15 mm of the measured values. For the three SOBPs considered, the maximum R80 deviation from measurement for GMC was −0.35 mm, RMC 0.5 mm, and RPB −0.1 mm. The minimum gamma pass using the 3%/3mm criterion for all the profiles was 94%. The dose comparison for heterogeneous inserts in low dose gradient regions showed dose differences greater than 10% at the distal edge of interface between RPB and GMC. The RMC showed improvement and agreed with GMC to within 7%.

Conclusion:

The RPB dosimetry show clinically significant differences (> 10%) from GMC and RMC estimates. The RMC algorithm is superior to the RPB dosimetry in heterogeneous media. We suspect modelling of the beam's halo may be responsible for a portion of the remaining discrepancy and that RayStation will reduce this discrepancy as they finalize the release.

Erik Traneus is employed as a Research Scientist at RaySearch Laboratories. The research build of the RayStation TPS used in the study was made available to the SCCA free of charge. RaySearch did not provide any monetary support other than a license to use the research build of the TPS.
SU‐F‐T‐156: Monte Carlo Simulation Using TOPAS for Synchrotron Based Proton Discrete Spot Scanning System
Authors: Moskvin V , Pirlepesov F , Tsiamas P , Axente M , Lukose R , Zhao L , Shin J , Farr J
Published: July 2016

Purpose:

This study provides an overview of the design and commissioning of the Monte Carlo (MC) model of the spot‐scanning proton therapy nozzle and its implementation for the patient plan simulation.

Methods:

The Hitachi PROBEAT V scanning nozzle was simulated based on vendor specifications using the TOPAS extension of Geant4 code. FLUKA MC simulation was also utilized to provide supporting data for the main simulation. Validation of the MC model was performed using vendor provided data and measurements collected during acceptance/commissioning of the proton therapy machine. Actual patient plans using CT based treatment geometry were simulated and compared to the dose distributions produced by the treatment planning system (Varian Eclipse 13.6), and patient quality assurance measurements. In‐house MATLAB scripts are used for converting DICOM data into TOPAS input files.

Results:

Comparison analysis of integrated depth doses (IDDs), therapeutic ranges (R90), and spot shape/sizes at different distances from the isocenter, indicate good agreement between MC and measurements. R90 agreement is within 0.15 mm across all energy tunes. IDDs and spot shapes/sizes differences are within statistical error of simulation (less than 1.5%). The MC simulated data, validated with physical measurements, were used for the commissioning of the treatment planning system. Patient geometry simulations were conducted based on the Eclipse produced DICOM plans.

Conclusion:

The treatment nozzle and standard option beam model were implemented in the TOPAS framework to simulate a highly conformal discrete spot‐scanning proton beam system.
SU‐F‐T‐164: Investigation of PRESAGE Formulation On Signal Quenching in a Proton Beam
Authors: Carroll M , Alqathami M , Ibbott G
Published: July 2016

Purpose:

The radiochromic polyurethane PRESAGE by Heuris Pharma has had limited applications with protons because of a dose response dependence on LET resulting in signal quenching in the Bragg peak. This is due to the radical initiator, a halocarbon, radically recombining in high‐LET irradiations. This study investigated the use of alternative halocarbons at various chemical concentrations to determine their significance in signal quenching.

Methods:

PRESAGE was manufactured in‐house and cast in small volume cuvettes (1×1×4cm^3). Several compositions were evaluated to determine the influence of the radical initiator component. Mixtures contained one of two halocarbons, chloroform or bromoform, at concentrations of 5%/10%/15%(w/w). A large volume, cylindrical PRESAGE dosimeter made following the mixture described by Heuris Pharma, 4cm(D)×8.5cm(H), was irradiated with 200‐MeV protons to study regions of low‐ and high‐LET along a 10cm spread out Bragg peak isodose profile. Depths corresponding to regions of low quenching (<3%) and high quenching (>20%) were determined. These depths were used for cuvette placement in a solid water phantom. Samples of each formulation were placed at each depth and irradiated to doses between 0 and 10Gy.

Results:

The cuvettes indicated different levels of quenching for different radical initiator types, concentrations, and total doses. Chloroform formulations showed reduced quenching from 29%(5%‐w/w) to 21%(15%‐w/w) while bromoform reduced quenching from 27%(5%‐w/w) to 17%(15%‐w/w). The reduction in quenching was found to be non‐linear with concentration of radical initiator. A quenching dose‐dependency was also found that changed with formulation. In all cases, quenching was relatively consistent from 0–5Gy but increased at 10Gy. The quenching decreased as concentrations of radical initiator increased.

Conclusion:

The radical initiator component in PRESAGE is correlated with the signal quenching observed in proton irradiations and formulation adjustments show promise as a method of reducing this quenching. Future work will further investigate concentration limits and optimize the formulation. Grant number 5RO1CA100835
SU‐F‐T‐180: Evaluation of a Scintillating Screen Detector for Proton Beam QA and Acceptance Testing
Authors: Ghebremedhin A , Taber M , Koss P , Camargo G , Ebstein S , Patyal B
Published: July 2016

Purpose:

To test the performance of a commercial scintillating screen detector for acceptance testing and Quality Assurance of a proton pencil beam scanning system.

Method:

The detector (Lexitek DRD 400) has 40cm × 40cm field, uses a thin scintillator imaged onto a 16‐bit scientific CCD with ∼0.5mm resolution. A grid target and LED illuminators are provided for spatial calibration and relative gain correction. The detector mounts to the nozzle with micron precision. Tools are provided for image processing and analysis of single or multiple Gaussian spots.

Results:

The bias and gain of the detector were studied to measure repeatability and accuracy. Gain measurements were taken with the LED illuminators to measure repeatability and variation of the lens‐CCD pair as a function with f‐stop. Overall system gain was measured with a passive scattering (broad) beam whose shape is calibrated with EDR film placed in front of the scintillator. To create a large uniform field, overlapping small fields were recorded with the detector translated laterally and stitched together to cover the full field. Due to the long exposures required to obtain multiple spills of the synchrotron and very high detector sensitivity, borated polyethylene shielding was added to reduce direct radiation events hitting the CCD. Measurements with a micro ion chamber were compared to the detector's spot profile. Software was developed to process arrays of Gaussian spots and to correct for radiation events.

Conclusion:

The detector background has a fixed bias, a small component linear in time, and is easily corrected. The gain correction method was validated with 2% accuracy. The detector spot profile matches the micro ion chamber data over 4 orders of magnitude. The multiple spot analyses can be easily used with plan data for measuring pencil beam uniformity and for regular QA comparison.
SU‐F‐T‐187: Quantifying Normal Tissue Sparing with 4D Robust Optimization of Intensity Modulated Proton Therapy
Authors: Newpower M , Ge S , Mohan R
Published: July 2016

Purpose:

To report an approach to quantify the normal tissue sparing for 4D robustly‐optimized versus PTV‐optimized IMPT plans.

Methods:

We generated two sets of 90 DVHs from a patient's 10‐phase 4D CT set; one by conventional PTV‐based optimization done in the Eclipse treatment planning system, and the other by an in‐house robust optimization algorithm. The 90 DVHs were created for the following scenarios in each of the ten phases of the 4DCT: ± 5mm shift along x, y, z; ± 3.5% range uncertainty and a nominal scenario. A Matlab function written by Gay and Niemierko was modified to calculate EUD for each DVH for the following structures: esophagus, heart, ipsilateral lung and spinal cord. An F‐test determined whether or not the variances of each structure's DVHs were statistically different. Then a t‐test determined if the average EUDs for each optimization algorithm were statistically significantly different.

Results:

T‐test results showed each structure had a statistically significant difference in average EUD when comparing robust optimization versus PTV‐based optimization. Under robust optimization all structures except the spinal cord received lower EUDs than PTV‐based optimization. Using robust optimization the average EUDs decreased 1.45% for the esophagus, 1.54% for the heart and 5.45% for the ipsilateral lung. The average EUD to the spinal cord increased 24.86% but was still well below tolerance.

Conclusion:

This work has helped quantify a qualitative relationship noted earlier in our work: that robust optimization leads to plans with greater normal tissue sparing compared to PTV‐based optimization. Except in the case of the spinal cord all structures received a lower EUD under robust optimization and these results are statistically significant. While the average EUD to the spinal cord increased to 25.06 Gy under robust optimization it is still well under the TD50 value of 66.5 Gy from Emami et al.

Supported in part by the NCI U19 CA021239.
SU‐F‐T‐189: Dosimetric Comparison of Spot‐Scanning Proton Therapy Techniques for Liver Tumors Close to the Skin Surface
Authors: Takao S , Matsuura T , Matsuzaki Y , Fujii Y , Fujii T , Katoh N , Shimizu S , Umegaki K , Shirato H
Published: July 2016

Purpose:

Spot‐scanning technique has been utilized to achieve conformal dose distribution to large and complicated tumors. This technique generally does not require patient‐specific devices such as aperture and compensator. The commercially available spot‐scanning proton therapy (SSPT) systems, however, cannot deliver proton beams to the region shallower than 4 g/cm2. Therefore some range compensation device is required to treat superficial tumors with SSPT. This study shows dosimetric comparison of the following treatment techniques: (i) with a tabletop bolus, (ii) with a nozzle‐mounted applicator, and (iii) without any devices and using intensity‐modulated proton therapy (IMPT) technique.

Methods:

The applicator composed of a combination of a mini‐ridge filter and a range shifter has been manufactured by Hitachi, Ltd., and the tabletop bolus was made by .decimal, Inc. Both devices have been clinically implemented in our facility. Three patients with liver tumors close to the skin surface were examined in this study. Each treatment plan was optimized so that the prescription dose of 76 Gy(RBE) or 66 Gy(RBE) would be delivered to 99% of the clinical target volume in 20 fractions. Three beams were used for tabletop bolus plan and IMPT plan, whereas two beams were used in the applicator plan because the gantry angle available was limited due to potential collision to patient and couch. The normal liver, colon, and skin were considered as organs at risk (OARs).

Results:

The target heterogeneity index (HI = D5/D95) was 1.03 on average in each planning technique. The mean dose to the normal liver was considerably less than 20 Gy(RBE) in all cases. The dose to the skin could be reduced by 20 Gy(RBE) on average in the IMPT plan compared to the applicator plan.

Conclusion:

It has been confirmed that all treatment techniques met the dosimetric criteria for the OARs and could be implemented clinically.
SU‐F‐T‐194: Analyzing the Effect of Range Shifter Air Gap On TPS Dose Modeling Accuracy in Superficial PBS Proton Therapy
Authors: Shirey R , Wu H
Published: July 2016

Purpose:

Treatment planning systems (TPS) may not accurately model superficial dose distributions of range shifted proton pencil beam scanning (PBS) treatments. Numerous patient‐specific QA tests performed on superficially treated PBS plans have shown a consistent overestimate of dose by the TPS. This study quantifies variations between TPS planned dose and measured dose as a function of range shifter air gap and treatment depths up to 5 cm.

Methods:

PBS treatment plans were created in the TPS to uniformly irradiate a volume of solid water. One plan was created for each range shifter position analyzed, and all plans utilized identical dose optimization parameters. Each optimized plan was analyzed in the TPS to determine the planned dose at varying depths. A PBS proton therapy system with a 3.5 cm lucite range shifter delivered the treatment plans, and a parallel plate chamber embedded in RW3 solid water measured dose at shallow depths for each air gap. Differences between measured and planned doses were plotted and analyzed.

Results:

The data show that the TPS more accurately models superficial dose as the air gap between the range shifter and patient surface decreases. Air gaps less than 10 cm have an average dose difference of only 1.6%, whereas air gaps between 10 and 20 cm differ by 3.0% and gaps greater than 20 cm differ by 4.4%.

Conclusion:

This study has shown that the TPS is unable to accurately model superficial dose with a large range shifter air gap. Dose differences greater than 3% will likely cause QA failure, as many institutions analyze patient QA with a 3%/3mm gamma analysis. For superficial PBS therapy, range shifter positions should be chosen to keep the air gap less then 10 cm when patient setup and gantry geometry allow.
SU‐F‐T‐201: Acceleration of Dose Optimization Process Using Dual‐Loop Optimization Technique for Spot Scanning Proton Therapy
Authors: Hirayama S , Fujimoto R
Published: July 2016

Purpose:

The purpose was to demonstrate a developed acceleration technique of dose optimization and to investigate its applicability to the optimization process in a treatment planning system (TPS) for proton therapy.

Methods:

In the developed technique, the dose matrix is divided into two parts, main and halo, based on beam sizes. The boundary of the two parts is varied depending on the beam energy and water equivalent depth by utilizing the beam size as a singular threshold parameter. The optimization is executed with two levels of iterations. In the inner loop, doses from the main part are updated, whereas doses from the halo part remain constant. In the outer loop, the doses from the halo part are recalculated. We implemented this technique to the optimization process in the TPS and investigated the dependence on the target volume of the speedup effect and applicability to the worst‐case optimization (WCO) in benchmarks.

Results:

We created irradiation plans for various cubic targets and measured the optimization time varying the target volume. The speedup effect was improved as the target volume increased, and the calculation speed increased by a factor of six for a 1000 cm3 target. An IMPT plan for the RTOG benchmark phantom was created in consideration of ±3.5% range uncertainties using the WCO. Beams were irradiated at 0, 45, and 315 degrees. The target's prescribed dose and OAR's Dmax were set to 3 Gy and 1.5 Gy, respectively. Using the developed technique, the calculation speed increased by a factor of 1.5. Meanwhile, no significant difference in the calculated DVHs was found before and after incorporating the technique into the WCO.

Conclusion:

The developed technique could be adapted to the TPS's optimization. The technique was effective particularly for large target cases.
SU‐F‐T‐206: Proton Treatment Techniques for Posterior Fossa Tumors: Consequences for LET and Dose/Volume Parameters for the Brainstem and Organs at Risk
Authors: Giantsoudi D , Adams J , MacDonald S , Paganetti H
Published: July 2016

Purpose:

In proton radiation therapy of posterior fossa tumors, to spare other sensitive structures, the preferred beam geometry results in placing the treatment field distal edge within or just beyond the brainstem, including in at least partially in the treatment volume. Concerns for brainstem toxicity are increased and a controversy exists as to weather the beam's distal edge should be placed within the brainstem or beyond it, to avoid elevated linear energy transfer (LET) and relative biological effectiveness (RBE) within the brainstem. The dosimetric efficacy of these techniques was examined, accounting for LET‐ and dose‐dependent variable RBE distributions.

Methods:

Three treatment planning techniques were applied in six ependymoma cases: (a) three‐field dose‐sparing, with beams’ distal edge within the brainstem; (b) three‐field LET‐sparing, using same beam directions as (a) but extended field ranges beyond the brainstem; (c) two‐posterior‐oblique LET‐sparing, with extended ranges as (b). Monte Carlo calculated dose, LET and RBE‐weighted dose distributions were compared.

Results:

Lower LET values in the brainstem were accompanied by higher median dose: 53.7 Gy[RBE] and 54.3 Gy[RBE] for techniques (b) and (c) versus 52.1 Gy[RBE] for (a). Accounting for variable RBE, a 15% increase of the brainstem volume receiving at least 60 Gy[RBE] was observed for technique (c) versus (a). Maximum variable‐RBE‐weighted brainstem dose was comparable for all techniques.

Conclusion:

Extending the treatment beam range beyond the brainstem, significantly increased its volume receiving high dose radiation, even when accounting for the decreased LET values. The dosimetric benefits of techniques limiting the brainstem dose may outweigh the impact of LET reduction achieved through this technique, especially since clinical consequences of increased LET at the end of range have not been proven yet.
SU‐F‐T‐211: Evaluation of a Dual Focusing Magnet System for the Treatment of Small Proton Targets
Authors: Nguyen TT , McAuley GA , Heczko S , Slater J , Wroe A
Published: July 2016

Purpose:

To investigate magnetic focusing for small volume proton targets using a doublet combination of quadrupole rare earth permanent magnet Halbach cylinder assemblies

Methods:

Monte Carlo computer simulations were performed using the Geant4 toolkit to compare dose depositions of proton beams transported through two focusing magnets or in their absence. Proton beams with energies of 127 MeV and initial diameters of 5, 8 and 10 mm were delivered through two identical focusing magnets similar to those currently in experimental use at Loma Linda University Medical Center. Analogous experiments used optimized configurations based on the simulation results. Dose was measured by a diode detector and Gafchromic EBT3 film and compared to simulation data. Based on results from the experimental data, an additional set of simulations was performed with an initial beam diameter of 18 mm and a two differing length magnets (40mm & 68mm).

Results:

Experimental data matched well with Monte Carlo simulations. However, under conditions necessary to produce circular beam spots at target depth, magnetically focused beams using two identical 40 mm length magnets did not meet all of our performance criteria of circular beam spots, improved peak to entrance (P/E) dose ratios and dose delivery efficiencies. The simulations using the longer 68 mm 2nd magnet yielded better results with 34% better P/E dose ratio and 20–50% better dose delivery efficiencies when compared to unfocused 10 mm beams.

Conclusion:

While magnetic focusing using two magnets with identical focusing power did not yield desired results, ongoing Monte Carlo simulations suggest that increasing the length of the 2nd magnet to 68 mm could improve P/E dose ratios and dose efficiencies. Future work includes additional experimental validation of the longer 2nd magnet setup as well as experiments with triplet magnet systems.

This project was sponsored with funding from the Department of Defense (DOD# W81XWH‐BAA‐10‐1).
SU‐F‐T‐215: An Investigation Of Multi‐Scanner CT Hounsfield Unit Calibration for Pencil Beam Scanning Proton Therapy Using 3D Gamma Analysis
Authors: Zhang J , Li X , Liu G , Liu Q , Liang J , Ding X
Published: July 2016

Purpose:

We compare and investigate the dosimetric impacts on pencil beam scanning (PBS) proton treatment plans generated with CT calibration curves from four different CT scanners and one averaged ‘global’ CT calibration curve.

Methods:

The four CT scanners are located at three different hospital locations within the same health system. CT density calibration curves were collected from these scanners using the same CT calibration phantom and acquisition parameters. Mass density to HU value tables were then commissioned in a commercial treatment planning system. Five disease sites were chosen for dosimetric comparisons at brain, lung, head and neck, adrenal, and prostate. Three types of PBS plans were generated at each treatment site using SFUD, IMPT, and robustness optimized IMPT techniques. 3D dose differences were investigated using 3D Gamma analysis.

Results:

The CT calibration curves for all four scanners display very similar shapes. Large HU differences were observed at both the high HU and low HU regions of the curves. Large dose differences were generally observed at the distal edges of the beams and they are beam angle dependent. Out of the five treatment sites, lung plans exhibits the most overall range uncertainties and prostate plans have the greatest dose discrepancy. There are no significant differences between the SFUD, IMPT, and the RO‐IMPT methods. 3D gamma analysis with 3%, 3 mm criteria showed all plans with greater than 95% passing rate. Two of the scanners with close HU values have negligible dose difference except for lung.

Conclusion:

Our study shows that there are more than 5% dosimetric differences between different CT calibration curves. PBS treatment plans generated with SFUD, IMPT, and the robustness optimized IMPT has similar sensitivity to the CT density uncertainty. More patient data and tighter gamma criteria based on structure location and size will be used for further investigation.
SU‐F‐T‐221: An Assessment of the Potential for Improved Local Control of Skull‐ Base Chordomas Via Reduction of the Proton Beam Range Uncertainty
Authors: Muller L , Soldner A , Kirk M , Fager M , Solberg T , Robert L , Dolney D
Published: July 2016

Purpose:

The beam range uncertainty presents a special challenge for proton therapy. Novel technologies currently under development offer strategies to reduce the range uncertainty [1,2]. This work quantifies the potential advantages that could be realized by such a reduction for dosimetrically challenging chordomas at the base of skull. Therapeutic improvement was assessed by evaluating tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP).

Methods:

Treatment plans were made for a modulated‐scanned proton delivery technique using the Eclipse treatment planning system. The prescription dose was 7920 cGy to the CTV. Three different range uncertainty scenarios were considered: 5 mm (3.5% of the beam range + 1 mm, representing current clinical practice, “Curr”), 2 mm (1.3%), and 1 mm (0.7%). For each of 4 patients, 3 different PTVs were defined via uniform expansion of the CTV by the value of the range uncertainty. Tumor control probability (TCP) and normal tissue complication probabilities (NTCPs) for organs‐at‐risk (OARs) were calculated using the Lyman‐Kutcher‐Burman[3] formalism and published model parameters [ref Terahara[4], quantec S10, Burman Red Journal v21 pp 123]. Our plan optimization strategy was to achieve PTV close to prescription while maintaining OAR NTCP values at or better than the Curr plan.

Results:

The average TCP values for the 5, 2, and 1 mm range uncertainty scenarios are 51%, 55% and 65%. The improvement in TCP for patients was between 4 and 30%, depending primarily on the proximity of the GTV to OAR. The average NTCPs for the brainstem and cord were about 4% and 1%, respectively, for all target margins.

Conclusion:

For base of skull chordomas, reduced target margins can substantially increase the TCP without increasing the NTCP. This work demonstrates the potential significance of a reduction in the range uncertainty for proton beams.
SU‐F‐T‐225: Is It Time to Have Pre‐Configured Therapeutic Beams Available in Commercial Treatment Planning Systems?
Authors: Ding G
Published: July 2016

Purpose:

Commissioning radiation beams requires considerable effort to obtain the beam data for beam configuration in a commercial treatment planning system. With the advances in technology, the manufacturer of accelerators now has the ability to adjust radiation beam parameters to meet pre‐determined specifications with high precision. This study aims to illustrate the feasibility of making pre‐configured radiation beams available in commercial treatment planning systems.

Methods:

In recent years, Varian has made a set of measured beam data from the TrueBeam accelerator available to users. Although the beam data are provided as “suggestive data” without warranty, the commissioned data measured by users have been shown to be in excellent agreement with the data set provided when the beams from the installed Linacs were adjusted to meet the beam specifications. An unofficial survey among Varian Linac TrueBeam users shows that the suggestive data set has been used with validation by users in some clinics. This indicates that radiation beams from a specified Linac can be standardized and pre‐configured in a treatment planning system.

Results:

Two newly installed Varian TrueBeam accelerators at two different centers were examined in which one set of commissioned beam data was obtained from measurements performed by an independent physics consulting company and the other was measured by local physicists in the department. All beams from both accelerators were tuned to meet the manufacturer's specifications. Discrepancies of less than 1% were found between the commissioned beam data from both accelerators and the suggestive data set provided by Varian.

Conclusion:

It may be feasible that radiation beams can be pre‐configured in commercial treatment planning systems. The radiation beam users will perform the beam validation and end‐to‐end tests instead of configuring beams. This framework can increase both the efficiency and the accuracy in commercial radiation treatment planning systems.
SU‐F‐T‐226: QA Management for a Large Institution with Multiple Campuses for FMEA
Authors: Tang G , Chan M , Lovelock D , Lim S , Febo R , DeLauter J , Both S , Li X , Ma R , Saleh Z , Song Y , Tang X , Xiong W , Hunt M , LoSasso T
Published: July 2016

Purpose:

To redesign our radiation therapy QA program with the goal to improve quality, efficiency, and consistency among a growing number of campuses at a large institution.

Methods:

A QA committee was established with at least one physicist representing each of our six campuses (22 linacs). Weekly meetings were scheduled to advise on and update current procedures, to review end‐to‐end and other test results, and to prepare composite reports for internal and external audits. QA procedures for treatment and imaging equipment were derived from TG Reports 142 and 66, practice guidelines, and feedback from ACR evaluations. The committee focused on reaching a consensus on a single QA program among all campuses using the same type of equipment and reference data. Since the recommendations for tolerances referenced to baseline data were subject to interpretation in some instances, the committee reviewed the characteristics of all machines and quantified any variations before choosing between treatment planning system (i.e. treatment planning system commissioning data that is representative for all machines) or machine‐specific values (i.e. commissioning data of the individual machines) as baseline data.

Results:

The configured QA program will be followed strictly by all campuses. Inventory of available equipment has been compiled, and additional equipment acquisitions for the QA program are made as needed. Dosimetric characteristics are evaluated for all machines using the same methods to ensure consistency of beam data where possible. In most cases, baseline data refer to treatment planning system commissioning data but machine‐specific values are used as reference where it is deemed appropriate.

Conclusion:

With a uniform QA scheme, variations in QA procedures are kept to a minimum. With a centralized database, data collection and analysis are simplified. This program will facilitate uniformity in patient treatments and analysis of large amounts of QA data campus‐wide, which will ultimately facilitate FMEA.
SU‐F‐T‐227: A Comprehensive Patient Specific, Structure Specific, Pre‐Treatment 3D QA Protocol for IMRT, SBRT and VMAT ‐ Clinical Experience
Authors: Gueorguiev G , Cotter C , Young M , Toomeh D , Khan F , Crawford B , Turcotte J , Mah'D M , Sharp G
Published: July 2016

Purpose:

To present a 3D QA method and clinical results for 550 patients.

Methods:

Five hundred and fifty patient treatment deliveries (400 IMRT, 75 SBRT and 75 VMAT) from various treatment sites, planned on Raystation treatment planning system (TPS), were measured on three beam‐matched Elekta linear accelerators using IBA's COMPASS system. The difference between TPS computed and delivered dose was evaluated in 3D by applying three statistical parameters to each structure of interest: absolute average dose difference (AADD, 6% allowed difference), absolute dose difference greater than 6% (ADD6, 4% structure volume allowed to fail) and 3D gamma test (3%/3mm DTA, 4% structure volume allowed to fail). If the allowed value was not met for a given structure, manual review was performed. The review consisted of overlaying dose difference or gamma results with the patient CT, scrolling through the slices. For QA to pass, areas of high dose difference or gamma must be small and not on consecutive slices. For AADD to manually pass QA, the average dose difference in cGy must be less than 50cGy. The QA protocol also includes DVH analysis based on QUANTEC and TG‐101 recommended dose constraints.

Results:

Figures 1–3 show the results for the three parameters per treatment modality. Manual review was performed on 67 deliveries (27 IMRT, 22 SBRT and 18 VMAT), for which all passed QA. Results show that statistical parameter AADD may be overly sensitive for structures receiving low dose, especially for the SBRT deliveries (Fig.1). The TPS computed and measured DVH values were in excellent agreement and with minimum difference.

Conclusion:

Applying DVH analysis and different statistical parameters to any structure of interest, as part of the 3D QA protocol, provides a comprehensive treatment plan evaluation.

Author G. Gueorguiev discloses receiving travel and research funding from IBA for unrelated to this project work. Author B. Crawford discloses receiving travel funding from IBA for unrelated to this project work.
SU‐F‐T‐232: Monthly Quality Assurance in External Beam Radiation Therapy Using a Single System
Authors: Ding K , Ji T , Iordachita I , Velarde E , Hyatt J , Wong J
Published: July 2016

Purpose:

Monthly quality assurance (QA) is time consuming for external beam radiation therapy, taking as long as 6–8 hours for each machine. It is due to the use and setup of multiple devices for different QA procedures. We have developed a single system with rotational capability for the measurement of both optical light and radiation which significantly reduces the time spent on Monthly QA.

Methods:

A single system using mirrors, a phosphor screen and a CCD camera is housed on a cylindrical motor so that it can rotate 360 degrees. For monthly QA, the system is placed on the patient couch of the medical accelerator with the plane of the phosphor screen at isocenter for all measurements. For optical QA such as optical distance indicator, room laser and light field, the optical image is collected directly with the camera. For radiation QA such as beam profile, MLC speed, picket‐fence test, collimator rotation, table rotation and gantry rotation, a brass build‐up plate is attached to the top of the phosphor screen. Two brass plates with islands of different thickness were designed for photon energy and electron energy constancy checks. Flex map, distortion map and uniformity map were developed to calibrate the motor bearing, camera/lens distortion, and the phosphor screen's measured response across the field.

Results:

Following the TG142 guidelines for monthly QA with our system, the overall run time is reduced from 6–8 hours to 1.5 hours. Our system's rotating design allows for quick testing of the gantry radiation isocenter test that is also independent of the sag of the gantry and the EPID.

Conclusion:

Our system significantly shortens the time needed for monthly QA by unifying the tests with a single system. Future work will be focused on extending the technology to Brachytherapy, IMRT and proton therapy QAs.

This work is funded in part by a sponsor research grant from JPLC who owns the Raven technology. John Wong is a co‐founder of JPLC.
SU‐F‐T‐240: EPID‐Based Quality Assurance for Dosimetric Credentialing
Authors: Miri N , Lehmann J , Vial P , Greer P
Published: July 2016

Purpose:

We propose a novel dosimetric audit method for clinical trials using EPID measurements at each center and a standardized EPID to dose conversion algorithm. The aim of this work is to investigate the applicability of the EPID method to different linear accelerator, EPID and treatment planning system (TPS) combinations.

Methods:

Combination of delivery and planning systems were three Varian linacs including one Pinnacle and two Eclipse TPS and, two ELEKTA linacs including one Pinnacle and one Monaco TPS. All Varian linacs had the same EPID structure and similarly for the ELEKTA linacs. Initially, dose response of the EPIDs was investigated by acquiring integrated pixel value (IPV) of the central area of 10 cm2 images versus MUs, 5‐400 MU. Then, the EPID to dose conversion was investigated for different system combinations. Square field size images, 2, 3, 4, 6, 10, 15, 20, 25 cm2 acquired by all systems were converted to dose at isocenter of a virtual flat phantom then the dose was compared to the corresponding TPS dose.

Results:

All EPIDs showed a relatively linear behavior versus MU except at low MUs which showed irregularities probably due to initial inaccuracies of irradiation. Furthermore, for all the EPID models, the model predicted TPS dose with a mean dose difference percentage of 1.3. However the model showed a few inaccuracies for ELEKTA EPID images at field sizes larger than 20 cm2.

Conclusion:

The EPIDs demonstrated similar behavior versus MU and the model was relatively accurate for all the systems. Therefore, the model could be employed as a global dosimetric method to audit clinical trials.

Funding has been provided from Department of Radiation Oncology, TROG Cancer Research and the University of Newcastle. Narges Miri is a recipient of a University of Newcastle postgraduate scholarship.
SU‐F‐T‐243: Major Risks in Radiotherapy. A Review Based On Risk Analysis Literature
Authors: López‐Tarjuelo J , Bouché‐Babiloni A , Morillo‐Macías V , Guasp‐Tortajada M , Iglesias‐Montenegro N , Monasor‐Denia P , Ferrer‐Albiach C
Published: July 2016

Purpose:

We present a literature review of risk analyses in radiotherapy to highlight the most reported risks and facilitate the spread of this valuable information so that professionals can be aware of these major threats before performing their own studies.

Methods:

We considered studies with at least an estimation of the probability of occurrence of an adverse event (O) and its associated severity (S). They cover external beam radiotherapy, brachytherapy, intraoperative radiotherapy, and stereotactic techniques. We selected only the works containing a detailed ranked series of elements or failure modes and focused on the first fully reported quartile as much. Afterward, we sorted the risk elements according to a regular radiotherapy procedure so that the resulting groups were cited in several works and be ranked in this way.

Results:

29 references published between 2007 and February 2016 were studied. Publication trend has been generally rising. The most employed analysis has been the Failure mode and effect analysis (FMEA). Among references, we selected 20 works listing 258 ranked risk elements. They were sorted into 31 groups appearing at least in two different works. 11 groups appeared in at least 5 references and 5 groups did it in 7 or more papers. These last sets of risks where choosing another set of images or plan for planning or treating, errors related with contours, errors in patient positioning for treatment, human mistakes when programming treatments, and planning errors.

Conclusion:

There is a sufficient amount and variety of references for identifying which failure modes or elements should be addressed in a radiotherapy department before attempting a specific analysis. FMEA prevailed, but other studies such as “risk matrix” or “occurrence × severity” analyses can also lead professionals’ efforts. Risk associated with human actions ranks very high; therefore, they should be automated or at least peer‐reviewed.
SU‐F‐T‐251: The Quality Assurance for the Heavy Patient Load Department in the Developing Country: The Primary Experience of An Entire Workflow QA Process Management in Radiotherapy
Authors: Xie J , Wang J , Peng J , Chen J , Hu W
Published: July 2016

Purpose:

To implement an entire workflow quality assurance (QA) process in the radiotherapy department and to reduce the error rates of radiotherapy based on the entire workflow management in the developing country.

Methods:

The entire workflow QA process management starts from patient registration to the end of last treatment including all steps through the entire radiotherapy process. Error rate of chartcheck is used to evaluate the the entire workflow QA process. Two to three qualified senior medical physicists checked the documents before the first treatment fraction of every patient. Random check of the treatment history during treatment was also performed. A total of around 6000 patients treatment data before and after implementing the entire workflow QA process were compared from May, 2014 to December, 2015.

Results:

A systemic checklist was established. It mainly includes patient's registration, treatment plan QA, information exporting to OIS(Oncology Information System), documents of treatment QAand QA of the treatment history. The error rate derived from the chart check decreases from 1.7% to 0.9% after our the entire workflow QA process. All checked errors before the first treatment fraction were corrected as soon as oncologist re‐confirmed them and reinforce staff training was accordingly followed to prevent those errors.

Conclusion:

The entire workflow QA process improved the safety, quality of radiotherapy in our department and we consider that our QA experience can be applicable for the heavily‐loaded radiotherapy departments in developing country.
SU‐F‐T‐263: Dosimetric Characteristics of the Cine Acquisition Mode of An A‐Si EPID
Authors: Bawazeer O , Sarasanandarajah S , Herath S , Kron T , Deb P
Published: July 2016

Purpose:

To investigate the dosimetric characteristics of Varian a‐Si‐500 electronic portal imaging device (EPID) operated in cine mode particularly considering linearity with delivered dose, dose rate, field size, phantom thickness, MLC speed and common IMRT fields.

Methods:

The EPID that attached to a Varian Clinac 21iX linear accelerator, was irradiated with 6 and 18 MV using 600 MU/min. Image acquisition is controlled by the IAS3 software, Trigger delay was 6 ms, BeamOnDelay and FrameStartDelay were zero. Different frame rates were utilized. Cine mode response was calculated using MATLAB as summation of mean pixel values in a region of interest of the acquired images. The performance of cine mode was compared to integrated mode and dose measurements in water using CC13 ionization chamber.

Results:

Figure1 illustrates that cine mode has nonlinear response for small MU, when delivering 10 MU was about 0.5 and 0.64 for 6 and 18 MV respectively. This is because the missing acquired images that were calculated around four images missing in each delivery. With the increase MU the response became linear and comparable with integrated mode and ionization chamber within 2%. Figure 2 shows that cine mode has comparable response with integrated mode and ionization chamber within 2% with changing dose rate for 10 MU delivered. This indicates that the dose rate change has no effect on nonlinearity of cine mode response. Except nonlinearity, cine mode is well matched to integrated mode response within 2% for field size, phantom thickness, MLC speed dependences.

Conclusion:

Cine mode has similar dosimetric characteristics to integrated mode with open and IMRT fields, and the main limitation with cine mode is missing images. Therefore, the calibration of EPID images with this mode should be run with large MU, and when IMRT verification field has low MU, the correction for missing images are required.
SU‐F‐T‐271: Comparing IMRT QA Pass Rates Before and After MLC Calibration
Authors: Mazza A , Perrin D , Fontenot J
Published: July 2016

Purpose:

To compare IMRT QA pass rates before and after an in‐house MLC leaf calibration procedure.

Methods:

The MLC leaves and backup jaws on four Elekta linear accelerators with MLCi2 heads were calibrated using the EPID‐based RIT Hancock Test as the means for evaluation. The MLCs were considered to be successfully calibrated when they could pass the Hancock Test with criteria of 1 mm jaw position tolerance, and 1 mm leaf position tolerance. IMRT QA results were collected pre‐ and postcalibration and analyzed using gamma analysis with 3%/3mm DTA criteria. AAPM TG‐119 test plans were also compared pre‐ and post‐calibration, at both 2%/2mm DTA and 3%/3mm DTA.

Results:

A weighted average was performed on the results for all four linear accelerators. The pre‐calibration IMRT QA pass rate was 98.3 ± 0.1%, compared with the post‐calibration pass rate of 98.5 ± 0.1%. The TG‐119 test plan results showed more of an improvement, particularly at the 2%/2mm criteria. The averaged results were 89.1% pre and 96.1% post for the C‐shape plan, 94.8% pre and 97.1% post for the multi‐target plan, 98.6% pre and 99.7% post for the prostate plan, 94.7% pre and 94.8% post for the head/neck plan.

Conclusion:

The patient QA results did not show statistically significant improvement at the 3%/3mm DTA criteria after the MLC calibration procedure. However, the TG‐119 test cases did show significant improvement at the 2%/2mm level.
SU‐F‐T‐283: A Novel Device to Enable Portal Dosimetry for Flattening Filter Free Beams
Authors: Faught A , Wu Q , Adamson J
Published: July 2016

Purpose:

Varian's electronic portal imaging device (EPID) based portal dosimetry tool is a popular and effective means of performing IMRT QA. EPIDs for older models of the TrueBeam accelerator utilize a 40cmx30cm Image Detection Unit (IDU) that saturates at the center for standard source to imager distances with high dose rate flattening filter free (FFF) beams. This makes portal dosimetry not possible and an alternative means of IMRT QA necessary. We developed a filter that would attenuate the beam to a dose rate measureable by the IDU for portal dosimetry IMRT QA.

Methods:

Multipurpose 304 stainless steel plates were placed on an accessory tray to attenuate the beam. Profiles of an open field measured on the IDU were acquired with varying number of plates to assess the thickness needed to reduce the maximum dose rates of 6XFFF and 10XFFF beams to measurable levels. A new portal dose image prediction (PDIP) model was commissioned based on open field measurements with plates in position, and a modified beam profile was input to portal dosimetry calibration at the console to empirically correct for attenuation and scatter. The portal dosimetry tool was used to assess agreement between predicted and measured doses for open 25×25cm2 fields and intensity modulated fields using 6XFFF and 10XFFF beams.

Results:

Thicknesses of 2.5cm and 3.8cm of steel were required to reduce the highest dose rates to a measureable level for 6XFFF and 10XFFF, respectively. Gamma analysis using a 3%/3mm relative criterion with the filter in place and using the new PDIP model resulted in 98.2% and 93.6% of pixels passing while intensity modulated fields showed passing rates of 98.2% and 99.0%.

Conclusion:

Use of the filter allows for portal dosimetry to be used for IMRT QA of FFF plans in place of purchasing a second option for IMRT QA.
SU‐F‐T‐247: Collision Risks in a Modern Radiation Oncology Department: An Efficient Approach to Failure Modes and Effects Analysis
Authors: Schubert L , Westerly D , Vinogradskiy Y , Aldridge J , Fisher C , Liu A
Published: July 2016

Purpose:

Collisions between treatment equipment and patients are potentially catastrophic. Modern technology now commonly involves automated remote motion during imaging and treatment, yet a systematic assessment to identify and mitigate collision risks has yet to be performed. Failure modes and effects analysis (FMEA) is a method of risk assessment that has been increasingly used in healthcare, yet can be resource intensive. This work presents an efficient approach to FMEA to identify collision risks and implement practical interventions within a modern radiation therapy department.

Methods:

Potential collisions (e.g. failure modes) were assessed for all treatment and simulation rooms by teams consisting of physicists, therapists, and radiation oncologists. Failure modes were grouped into classes according to similar characteristics. A single group meeting was held to identify implementable interventions for the highest priority classes of failure modes.

Results:

A total of 60 unique failure modes were identified by 6 different teams of physicists, therapists, and radiation oncologists. Failure modes were grouped into four main classes: specific patient setups, automated equipment motion, manual equipment motion, and actions in QA or service mode. Two of these classes, unusual patient setups and automated machine motion, were identified as being high priority in terms severity of consequence and addressability by interventions. The two highest risk classes consisted of 33 failure modes (55% of the total). In a single one hour group meeting, 6 interventions were identified. Those interventions addressed 100% of the high risk classes of failure modes (55% of all failure modes identified).

Conclusion:

A class‐based approach to FMEA was developed to efficiently identify collision risks and implement interventions in a modern radiation oncology department. Failure modes and interventions will be listed, and a comparison of this approach against traditional FMEA methods will be presented.