A benchmarking method to evaluate the accuracy of a commercial proton monte carlo pencil beam scanning treatment planning system

Abstract

AcurosPT is a Monte Carlo algorithm in the Eclipse 13.7 treatment planning system, which is designed to provide rapid and accurate dose calculations for proton therapy. Computational run‐time in minimized by simplifying or eliminating less significant physics processes. In this article, the accuracy of AcurosPT was benchmarked against both measurement and an independent MC calculation, TOPAS. Such a method can be applied to any new MC calculation for the detection of potential inaccuracies. To validate multiple Coulomb scattering (MCS) which affects primary beam broadening, single spot profiles in a Solidwater® phantom were compared for beams of five selected proton energies between AcurosPT, measurement and TOPAS. The spot Gaussian sigma in AcurosPT was found to increase faster with depth than both measurement and TOPAS, suggesting that the MCS algorithm in AcurosPT overestimates the scattering effect. To validate AcurosPT modeling of the halo component beyond primary beam broadening, field size factors (FSF) were compared for multi‐spot profiles measured in a water phantom. The FSF for small field sizes were found to disagree with measurement, with the disagreement increasing with depth. Conversely, TOPAS simulations of the same FSF consistently agreed with measurement to within 1.5%. The disagreement in absolute dose between AcurosPT and measurement was smaller than 2% at the mid‐range depth of multi‐energy beams. While AcurosPT calculates acceptable dose distributions for typical clinical beams, users are cautioned of potentially larger errors at distal depths due to overestimated MCS and halo implementation.

Validation and application of a fast Monte Carlo algorithm for assessing the clinical impact of approximations in analytical dose calculations for pencil beam scanning proton therapy

“…Some fast MC codes also increase computational efficiency by taking advantage of various modern parallel processing technologies . Recently, commercial vendors have also released fast MC codes in their TPSs (e.g., Eclipse (Varian, Palo Alto, CA, USA) and Raystation (Raysearch Lab, Stockholm, Sweden)) . These technological advances make fast MC calculation feasible for routine clinical use.…”

“…[26][27][28][29] Recently, commercial vendors have also released fast MC codes in their TPSs (e.g., Eclipse (Varian, Palo Alto, CA, USA) and Raystation (Raysearch Lab, Stockholm, Sweden)). 30,31 These technological advances make fast MC calculation feasible for routine clinical use. However, the fast MC codes are confined to a few research institutions and limited to post-planning dose calculation.…”

Calculation of clinical dose distributions in proton therapy from microdosimetry

“…This information can be obtained through Monte Carlo simulations of the proton transport in the patient. Some TPSs are able to provide that information . However, we have developed a kernel‐based algorithm for the spectral fluence at each point given a proton arriving to the patient surface.…”

“…The TPS provides the information about the beam lateral width—to be convolved with our lateral model. The number of protons prior to arrive to the patient surface can be estimated according to the number of monitor units (MU) for each spot so that we can obtain . We present comparisons of dose distributions obtained by the: (a) microdosimetric method presented in Eqs.…”

“…Some TPSs are able to provide that information. 21,22 However, we have developed a kernel-based algorithm for the spectral fluence at each point given a proton arriving to the patient surface. Here we provide an outline of this, although it is fully presented in a separate work.…”