Out-of-field dose calculation by a commercial treatment planning system and comparison by monte carlo simulation for varian TrueBeam^®

Abstract

Purpose:The calculation accuracy of treatment planning systems (TPSs) drops drastically when the points outside the field edges are considered. The real accuracy of a TPS and linear accelerator (linac) combination for regions outside the field edge is a subject which demands more study. In this study, the accuracy of out-of-field dose calculated by a TPS, used with a TrueBeam® (TB) linac, is quantified.Materials and Methods:For dose calculation, Eclipse™ version 13.7 commissioned for TB machine was used. For comparison, Monte Carlo (MC) methods, as well as the measurements, were used. The VirtuaLinac, a Geant 4-based MC program which is offered as a cloud solution, is used for the generation of input phase-space (PS) files. This PS file was imported into PRIMO (PENELOPE based MC program) for the simulation of out-of-field dose.Results:In this study, the accuracy of the out-of-field dose calculated by a TPS for a TB linac was estimated. As per the results in comparison with MC simulations, the TPS underestimated the dose by around 45% on an average for the off-axis-distance range considered in this study. As the off-axis distance increased, the underestimation of the dose also increased.Conclusion:In this work, it was observed that the TPS underestimates doses beyond the edges of treatment fields for a clinical treatment executed on a TB machine. This indicates that the out-of-field dose from TPSs should only be used with a clear understanding of the inaccuracy of dose calculations beyond the edge of the field.

Assessment of Fetal Dose and Health Effect to the Fetus from Breast Cancer Radiotherapy during Pregnancy

“…First, treatment planning systems are known to underestimate the collimator scatter and scatter from other components of the beam line, which directly affect the out-of-field dose calculations. Therefore, for organs further away from the target, the dose discrepancies increased, in accordance with the previous studies [14,15]. Second, in the treatment planning process, manual contouring was done to delineate the organs and structures of interest.…”

Development of clinical application program for radiotherapy induced cancer risk calculation using Monte Carlo engine in volumetric-modulated arc therapy

“…We utilized a previously developed clinically available automatic VMAT QA system for this study [ 37 ]. The system is designed to re-calculate the beam sequence of equipment and treatment plan using the Monte Carlo engine, so it is possible to accurately calculate and evaluate scatter and leakage radiation, difficult to calculate in TPS [ 38 ]. The basic program was designed for QA, so the module was additionally configured to enable dose calculation using patient CT data.…”

Avaliação das doses e do risco subsequente de desenvolvimento de câncer em órgãos fora do campo de tratamento na radioterapia de linfoma de Hodgkin

“…A tabela 1 apresenta as doses em órgãos de interesse, dentro e fora do campo de tratamento, obtidas experimentalmente a partir de medições em TLDs posicionados em um fantoma irradiado em simulações do tratamento radioterápico do linfoma de Hodgkin, e as respectivas distâncias dos TLD à borda do campo. inferiores em relação às doses medidas com TLDs [21][22][23][24]. O cálculo da dose feito pelo sistema de planejamento utilizado é baseado em modelos de convolução separados para fótons primários e fótons extra focais dispersos (fótons não originados no ponto focal do alvo).…”

“…Essa pequena diferença percentual pode ser explicada pelo fato de o cérebro estar no eixo central de irradiação, numa posição mais próxima da borda do campo do que os demais órgãos avaliados. Na literatura tem sido reportada a necessidade de correções para as regiões fora do campo[21][22][23]. Howell et al, Huang…”