A standardized commissioning framework of Monte Carlo dose calculation algorithms for proton pencil beam scanning treatment planning systems

Abstract

Purpose: Treatment planning systems (TPSs) from different vendors can involve different implementations of Monte Carlo dose calculation (MCDC) algorithms for pencil beam scanning (PBS) proton therapy. There are currently no guidelines for validating non-water materials in TPSs. Furthermore, PBSspecific parameters can vary by 1-2 orders of magnitude among different treatment delivery systems (TDSs). This paper proposes a standardized framework on the use of commissioning data and steps to validate TDS-specific parameters and TPS-specific heterogeneity modeling to potentially reduce these uncertainties. Methods: A standardized commissioning framework was developed to commission the MCDC algorithms of RayStation 8A and Eclipse AcurosPT v13.7.20 using water and non-water materials. Measurements included Bragg peak depth-dose and lateral spot profiles and scanning field outputs for Varian ProBeam. The phase-space parameters were obtained from in-air measurements and the number of protons per MU from output measurements of 10 9 10 cm 2 square fields at a 2 cm depth. Spot profiles and various PBS field measurements at additional depths were used to validate TPS. Human tissues in TPS, Gammex phantom materials, and artificial materials were used for the TPS benchmark and validation. Results: The maximum differences of phase parameters, spot sigma, and divergence between MCDC algorithms are below 4.5 µm and 0.26 mrad in air, respectively. Comparing TPS to measurements at depths, both MC algorithms predict the spot sigma within 0.5 mm uncertainty intervals, the resolution of the measurement device. Beam Configuration in AcurosPT is found to underestimate number of protons per MU by~2.5% and requires user adjustment to match measured data, while RayStation is within 1% of measurements using Auto model. A solid water phantom was used to validate the range accuracy of non-water materials within 1% in AcurosPT. Conclusions: The proposed standardized commissioning framework can detect potential issues during PBS TPS MCDC commissioning processes, and potentially can shorten commissioning time and improve dosimetric accuracies. Secondary MCDC can be used to identify the root sources of disagreement between primary MCDC and measurement.

Producing a Beam Model of the Varian ProBeam Proton Therapy System using TOPAS Monte Carlo Toolkit

“…The Varian ProBeam beamline was characterized during commissioning of each gantry room and provided the necessary measurements to specify beam characteristics in TOPAS MC toolkit 23,24 . The distance from the snout of the gantry to the isocenter was 420 mm.…”

“…The actual plan delivered 100 MU per spot position. The dose was scored at 20 mm depth with voxel thickness (z‐direction) of 1.16 mm, and diameter of 20 mm to represent the PPC40 ionization chamber 24 . The number of protons per MU for each commissioned energy was determined by using:…”

“…The Varian ProBeam beamline was characterized during commissioning of each gantry room and provided the necessary measurements to specify beam characteristics in TOPAS MC toolkit. 23,24 The distance from the snout of the gantry to the isocenter was 420 mm. The IDD curves at a range of energies from 70 to 242 MeV single spot beams were measured in a water phantom using the IBA string ray ionization chamber (accuracy within 1% in comparison to the gold standard, parallel plate chamber) 25,26 with an active detection diameter of 120 mm thickness and electrode spacing of 1 mm.…”

Beam characteristics of the first clinical 360° rotational single gantry room scanning pencil beam proton treatment system and comparisons against a multi‐room system

“…Validation of the modeling comprises the verifications of the computed IDDs and calculated dose in difference conditions and field sizes with both PCS and AcurosPT models 11–16 ; the overall accuracy of the AcurosPT‐computed treatment planning and dose delivery using realistic clinical plans as well as the end‐to‐end tests for different open beams and beams with different range shifters and air gaps 17,18 . The halo effects of the beams beyond the modeled profile were examined by comparison between the AcurosPT computed and measured doses with different field sizes and energies at near the surface 8 .…”

Empirical quenching correction in radiochromic silicone-based three-dimensional dosimetry of spot-scanning proton therapy

“…The dosimeters were the symbol '-' appears were used to parametrize the correction model. dose depth were not considered in the parametrization of the QCF curve for a similar reason; the steep dose gradient would make it more susceptible to uncertainties in the MC beam model and positioning errors between simulated and measured dose distributions [26,[35][36][37][38]. In future experiments, positioning uncertainty could be minimized by placing markers in the dosimeters, which appear in both cone-beam and optical CT scans.…”