RECORDS: improved Reporting of montE CarlO RaDiation transport Studies: Report of the <scp>AAPM</scp> Research Committee Task Group 268

Purpose A good Monte Carlo model with an accurate head shielding model is important in estimating the long‐term risks of unwanted radiation exposure during radiation therapy. The aim of this paper was to validate the Monte Carlo simulation of a TrueBeam linear accelerator (linac) head shielding model. We approach this by evaluating the accuracy of out‐of‐field dose predictions at extended distances which are comprised of scatter from within the patient and treatment head leakage and thus reflect the accuracy of the head shielding model. We quantify the out‐of‐field dose of a TrueBeam linac for low‐energy photons, 6X and 6X‐FFF beams, and compare measurements to Monte Carlo simulations using Varian VirtuaLinac that include a realistic head shielding model, for a variety of jaw sizes and angles up to a distance of 100 cm from the isocenter, in both positive and negative directions. Given the high value and utility of the VirtuaLinac model, it is critical that this model is validated thoroughly and the results be available to the medical physics community. Materials and method Simulations were done using VirtuaLinac, the GEANT4‐based Monte Carlo model of the TrueBeam treatment head from Varian Medical Systems, and an in‐house GEANT4‐based code. VirtuaLinac included a detailed model of the treatment head shielding and was run on the Amazon Web Services cloud to generate spherical phase space files surrounding the treatment head. These phase space files were imported into the in‐house code, which modeled the measurement setup with a solid water buildup, the carbon fiber couch, and the gantry stand. For each jaw size (2 × 2 cm2, 4 × 4 cm2, 10 × 10 cm2, and 20 × 20 cm2) and angular setting (0°, 90°, 45°, 135°), the dose was calculated at intervals of 5 cm along each measurement direction. Results For the 10 × 10 cm2 jaw size, both 6X and 6X‐FFF showed very good agreement between simulation and measurement in both in‐plane directions, with no apparent systematic bias. The percentage deviations for these settings were as follows: (mean, STDEV, maximum) (8.34, 6.44, 24.84) for 6X and (13.21, 8.93, 35.56) for 6X‐FFF. For all jaw sizes, simulation agreed well in the in‐plane direction going away from the gantry, but, some deviations were observed moving toward the gantry at larger distances. At larger distances, for the jaw sizes smaller than 10 × 10 cm2, the simulation underestimates the dose compared with measurement, while for jaw sizes larger than 10 × 10 cm2, it overestimates dose. For all comparisons between ±50 cm from isocenter, average absolute agreement between simulation and measurement was better than 28%. Conclusion We have validated the Varian VirtuaLinac's head shielding model via out‐of‐field doses and quantified the differences between TrueBeam head shielding model created out‐of‐field doses and measurements for an extended distance of 100 cm.

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“…Per AAPM TG 268, a table containing the parameters used for the Monte Carlo simulation is given in Table .…”

Section: Resultsmentioning

confidence: 99%

Part II: Verification of the TrueBeam head shielding model in Varian VirtuaLinac via out‐of‐field doses

et al. 2019

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“…39 The MC details are summarized in Table I following the recommendations of the RECORDS AAPM TG-268 report. 40 Further information about the transport parameters, variance reduction tools, etc. is described elsewhere.…”

Section: E1 Hvlmentioning

confidence: 99%

On the use of the absorbed depth‐dose measurements in the beam calibration of a surface electronic high‐dose‐rate brachytherapy unit, a Monte Carlo‐based study

Valdes-Cortez¹,

Niatsetski²,

Ballester³

et al. 2019

Medical Physics

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Purpose To evaluate the use of the absorbed depth‐dose as a surrogate of the half‐value layer in the calibration of a high‐dose‐rate electronic brachytherapy (eBT) equipment. The effect of the manufacturing tolerances and the absorbed depth‐dose measurement uncertainties in the calibration process are also addressed. Methods The eBT system Esteya® (Elekta Brachytherapy, Veenendaal, The Netherlands) has been chosen as a proof‐of‐concept to illustrate the feasibility of the proposed method, using its 10 mm diameter applicator. Two calibration protocols recommended by the AAPM (TG‐61) and the IAEA (TRS‐398) for low‐energy photon beams were evaluated. The required Monte Carlo (MC) simulations were carried out using PENELOPE2014. Several MC simulations were performed modifying the flattening filter thickness and the x‐ray tube potential, generating one absorbed depth‐dose curve and a complete set of parameters required in the beam calibration (i.e., HVL, backscatter factor (Bw), and mass energy‐absorption coefficient ratios (µen/ρ)water,air), for each configuration. Fits between each parameter and some absorbed dose‐ratios calculated from the absorbed depth‐dose curves were established. The effect of the manufacturing tolerances and the absorbed dose‐ratio uncertainties over the calibration process were evaluated by propagating their values over the fitting function, comparing the overall calibration uncertainties against reference values. We proposed four scenarios of uncertainty (from 0% to 10%) in the dose‐ratio determination to evaluate its effect in the calibration process. Results The manufacturing tolerance of the flattening filter (±0.035 mm) produces a change of 1.4% in the calculated HVL and a negligible effect over the Bw, (µen/ρ)water,air, and the overall calibration uncertainty. A potential variation of 14% of the electron energies due to manufacturing tolerances in the x‐ray tube (69.5 ± ~10 keV) generates a variation of 10% in the HVL. However, this change has a negligible effect over the Bw and (µen/ρ)water,air, adding 0.1% to the overall calibration uncertainty. The fitting functions reproduce the data with an uncertainty (k = 2) below 1%, 0.5%, and 0.4% for the HVL, Bw, and (µen/ρ)water,air, respectively. The four studied absorbed dose‐ratio uncertainty scenarios add, in the worst‐case scenario, 0.2% to the overall uncertainty of the calibration process. Conclusions This work shows the feasibility of using the absorbed depth‐dose curve in the calibration of an eBT system with minimal loss of precision.

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“…Consequently, in order to interpret results and accuracy of MC simulations and to compare with measurements at different institutions, these settings must be reported. Guidance can be found in the report of the AAPM Task group 268 entitled “Towards complete and accurate reporting of MC radiation transport studies” …”

Section: Monte Carlo Calculationsmentioning

confidence: 99%

Report of a National Cancer Institute special panel: Characterization of the physical parameters of particle beams for biological research

et al. 2018

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Purpose To define the physical parameters needed to characterize a particle beam in order to allow intercomparison of different experiments performed using different ions at the same facility and using the same ion at different facilities. Methods At the request of the National Cancer Institute (NCI), a special panel was convened to review the current status of the field and to provide suggested metrics for reporting the physical parameters of particle beams to be used for biological research. A set of physical parameters and measurements that should be performed by facilities and understood and reported by researchers supported by NCI to perform pre‐clinical radiobiology and medical physics of heavy ions were generated. Results Standard measures such as radiation delivery technique, beam modifiers used, nominal energy, field size, physical dose and dose rate should all be reported. However, more advanced physical measurements, including detailed characterization of beam quality by microdosimetric spectrum and fragmentation spectra, should also be established and reported. Details regarding how such data should be incorporated into Monte Carlo simulations and the proper reporting of simulation details are also discussed. Conclusions In order to allow for a clear relation of physical parameters to biological effects, facilities and researchers should establish and report detailed physical characteristics of the irradiation beams utilized including both standard and advanced measures. Biological researchers are encouraged to actively engage facility staff and physicists in the design and conduct of experiments. Modeling individual experimental setups will allow for the reporting of the uncertainties in the measurement or calculation of physical parameters which should be routinely reported.

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RECORDS: improved Reporting of montE CarlO RaDiation transport Studies: Report of the AAPM Research Committee Task Group 268

Cited by 216 publications

References 13 publications

Part II: Verification of the TrueBeam head shielding model in Varian VirtuaLinac via out‐of‐field doses

Part II: Verification of the TrueBeam head shielding model in Varian VirtuaLinac via out‐of‐field doses

On the use of the absorbed depth‐dose measurements in the beam calibration of a surface electronic high‐dose‐rate brachytherapy unit, a Monte Carlo‐based study

Report of a National Cancer Institute special panel: Characterization of the physical parameters of particle beams for biological research

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