Update of the CLRP Monte Carlo TG‐43 parameter database for high‐energy brachytherapy sources

Abstract

To update and extend version 2 of the Carleton Laboratory for Radiotherapy Physics (CLRP) TG-43 dosimetry database (CLRP_TG43v2) for high-energy (HE, ≥ 50 keV) brachytherapy sources (1 169 Yb, 23 192 Ir, 5 137 Cs, and 4 60 Co) using egs_brachy, an open-source EGSnrc application. A comprehensive dataset of TG-43 parameters is compiled, including detailed source descriptions, dose-rate constants, radial dose functions, 1D and 2D anisotropy functions, along-away dose-rate tables, Primary and Scatter Separated (PSS) dose tables, and mean photon energies escaping each source. The database also documents the source models which are freely distributed with egs_brachy. Acquisition and Validation Methods: Datasets are calculated after a recoding of the source geometries using the egs++ geometry package and its egs_brachy extensions. Air kerma per history is calculated in a 10 × 10 × 0.05 cm 3 voxel located 100 cm from the source along the transverse axis and then corrected for the lateral and thickness dimensions of the scoring voxel to give the air kerma on the central axis at a point 100 cm from the source's mid-point. Full-scatter water phantoms with varying voxel resolutions in cylindrical coordinates are used for dose calculations. Most data (except for 60 Co) are based on the assumption of charged particle equilibrium and ignore the potentially large effects of electron transport very close to the source and dose from initial beta particles. These effects are evaluated for four representative sources. For validation, data are compared to those from CLRP_TG43v1 and published data. Data Format and Access: Data are available at https://physics.carleton. ca/clrp/egs_brachy/seed_database_v2 or http://doi.org/10.22215/clrp/tg43v2 including in Excel (.xlsx) spreadsheets, and are presented graphically in comparisons to previously published data for each source. Potential Applications: The CLRP_TG43v2 database has applications in research, dosimetry, and brachytherapy planning. This comprehensive update provides the medical physics community with more precise and in some cases more accurate Monte Carlo (MC) TG-43 dose calculation parameters, as well as fully benchmarked and described source models which are distributed with egs_brachy.

RapidBrachyTG43: A Geant4‐based TG‐43 parameter and dose calculation module for brachytherapy dosimetry

“…Dose-rate constant values agreed with literature data produced from Monte Carlo simulations with the same geometry within 1%, except for the A86 60 Co source, which produced a dose-rate constant 1.2% higher than egs_brachy. 10 The dose-rate constant for both high-energy sources also agreed with 1% to the consensus values from the HEBD report. 3 However, the SelectSeed value for Λ was about 3% lower than the TG43U1 Supplement 2 consensus.…”

“…The reference datasets chosen for comparison were obtained from the CLRP TG-43 Parameter Database for Brachytherapy version 2, generated by egs_brachy. 9,10 All points of the radial dose function g L (r) for each source remained within 1% of the benchmark data dataset within 1%, except for the BEBIG A86, where g L (r) differed by 1.1% from the benchmark dataset at the closest value of r, 0.2 cm.…”

“…Track-length estimation approximates absorbed dose by approximating it with collision kerma, which only equalize as charged particle equilibrium is reached. Though both methods have been shown to agree for 60 Co well within 1% for r > 1 cm, 21 the discontinuity suggests that a larger threshold radius should be used for 60 Co to ensure a continuous radial dose function.Recent findings from Safigholi et al 10 support that dose and collision kerma differ by about 1% at r = 1 cm, and a convergence of the radial dose function produced by track length estimation and interaction scoring occurring at 1 cm < r < 2 cm. Monte Carlo tools have been at the cornerstone of dosimetry parameter datasets generation since the inception of TG-43, and published data for sources generally utilize a range of Monte Carlo toolkits to derive the necessary Ḋww maps.…”

“…Similarly, the A86's 2D anisotropy function at r = 1 cm remained within 1% of the benchmark at low angles near the head F I G U R E 1 A comparison of RapidBrachyTG43-calculated radial dose function and 2D anisotropy function at r = 1 cm for the three sources considered, in comparison with the same dataset as calculated by egs_brachy and published to the CLRP database version 2. 9,10 of the source, exceeded 1% discrepancy at 𝜃 ≥ 170 • , and displayed a maximum discrepancy of 5.0% at 𝜃 = 5%.…”

“…Other nonofficial databases of source parameter datasets are maintained by GEC-ESTRO BRAPHYQS, 6 University of Valencia, 7 and the Carleton Laboratory for Radiotherapy Physics (CLRP) TG-43 Parameter Database for Brachytherapy, versions 1 8 and 2. 9,10 RapidBrachyMCTPS 11,12 is a brachytherapy TPS, capable of treatment planning and dose calculation beyond the TG-43 formalism, compliant with the AAPM recommendations on model-based dose calculation algorithms outlined in the AAPM Task Group No. 186 (TG-186) report.…”