Benchmark measurements and simulations of dose perturbations due to metallic spheres in proton beams

Abstract

Monte Carlo simulations are increasingly used for dose calculations in proton therapy due to its inherent accuracy. However, dosimetric deviations have been found using Monte Carlo code when high density materials are present in the proton beam line. The purpose of this work was to quantify the magnitude of dose perturbation caused by metal objects. We did this by comparing measurements and Monte Carlo predictions of dose perturbations caused by the presence of small metal spheres in several clinical proton therapy beams as functions of proton beam range, spread-out Bragg peak width and drift space. Monte Carlo codes MCNPX, GEANT4 and Fast Dose Calculator (FDC) were used. Generally good agreement was found between measurements and Monte Carlo predictions, with the average difference within 5% and maximum difference within 17%. The modification of multiple Coulomb scattering model in MCNPX code yielded improvement in accuracy and provided the best overall agreement with measurements. Our results confirmed that Monte Carlo codes are well suited for predicting multiple Coulomb scattering in proton therapy beams when short drift spaces are involved.

Carbon ion radiotherapy using fiducial markers for prostate cancer in Osaka HIMAK: Treatment planning

“…This is because multiple coulomb scattering of protons occurs in a greater amount than carbons. 11 , 12 , 14 On the other hand, contribution of fiducial markers to dose distributions of carbon ions is small, which is similar to the results of another study. 16 In the present study, the DVH of a target was simulated to evaluate the effect of markers on dose coverage to a target.…”

“…The dose perturbation in the case of carbon ions evaluated in our study is much smaller than those that were reported in the case of protons. This is because multiple coulomb scattering of protons occurs in a greater amount than carbons 11,12,14 . On the other hand, contribution of fiducial markers to dose distributions of carbon ions is small, which is similar to the results of another study 16 .…”

“…9,10 The present study evaluated the effect of two types of fiducial markers, GA and VISICOIL (RadioMed), on dose distributions measured by films. Several studies evaluating the dose perturbation due to fiducial markers for proton beams have been reported [10][11][12][13][14][15] ; however, only one study for carbon ion beams has been reported. 16 Treatment plans with the bsPTV for prostate cancer are created using single-field uniform dose (SFUD) algorithm since this algorithm is more robust against uncertainties than intensity-modulated particle therapy (IMPT).…”

Inter-Institutional Comparison of Personalized Risk Assessments for Second Malignant Neoplasms for a 13-Year-Old Girl Receiving Proton versus Photon Craniospinal Irradiation

“…Equivalent dose from secondary neutrons was calculated in each voxel using the Monte Carlo Proton Radiotherapy Treatment Planning (MCPRTP) system [ 9 , 23 , 26 , 27 ]. The MCPRTP system was modified prior to this study to include a lattice tally instead of a mesh tally to calculate dose within the patient [ 28 ], an upgrade of the dose engine to version 2.7c of the Monte Carlo N-Particle eXtended code [ 29 ], more-specific isotopic materials cards that call cross-section tables when available, the most up-to-date data libraries, an improved multiple Coulomb scattering algorithm [ 30 , 31 ], a reduced bin size for more precise proton stopping power, and removal of triton and 3 He tracking. The system was validated by comparing its results to the results of previous studies and measured data.…”

The physics of proton therapy

“…Others have examined the effects of MCS in larger metal objects on clinical proton beams and characterized the suitability of approximate methods to predict MCS in practical clinical applications (Herault et al , 2005; Stankovskiy et al , 2009; Newhauser et al , 2013). …”