Differential‐pencil‐beam dose calculations for charged particles

Abstract

The use of a convolution or differential-pencil-beam (DPB) algorithm has been studied for charged-particle dose calculations as a means of more accurately modeling the effects of multiple scattering. Such effects are not reflected in current charged-particle dose calculations since these calculations rely on depth-dose data measured in homogeneous water-equivalent phantoms and use ray-tracing techniques to calculate the water-equivalent pathlength from patient CT data. In this study, isodose plots were generated from three-dimensional dose calculations using Monte Carlo, DPB, and standard ray-tracing methods for a 4-cm modulated 150-MeV proton beam incident on both homogenous and heterogeneous phantoms. To simulate therapy conditions with charged particles, these studies included cases where compensating boluses were introduced to modify the particle range across the treatment field. Results indicate that multiple-scattering effects, including increased penumbral width as a function of beam penetration and the "smearing" of isodose distributions downstream from complex heterogeneities, are well modeled by the DPB algorithm. The DPB algoirthm may also be used to obtain more useful estimates of the dose uncertainty in regions near the end of the beam's range downstream from complex heterogeneities than can be derived from standard ray-tracing calculations.

Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy

“…29 The in-air fluence distribution was analytically modeled for the wobbling system. 30,31 The kernel, which is a dose distribution for a virtual pencil beam, is defined as…”

The NAC proton treatment planning system

“…Limitations of rayline tracing models are well documented [7, 11] and relate to the fact that they use data that are measured in homogeneous water phantoms and therefore ignore the differences in multiple scattering effects resulting from patient inhomogeneities. However rayline-tracing still offers a reasonable compromise to complicated and time consuming pencil beam and Monte Carlo calculations [7,12] especially if the region of interest does not contain very complex heterogeneities.…”

“…Limitations of rayline tracing models are well documented [7, 11] and relate to the fact that they use data that are measured in homogeneous water phantoms and therefore ignore the differences in multiple scattering effects resulting from patient inhomogeneities. However rayline-tracing still offers a reasonable compromise to complicated and time consuming pencil beam and Monte Carlo calculations [7,12] especially if the region of interest does not contain very complex heterogeneities.In the proton dose calculation module, the CT data are converted to relative electron densities using optimised calibration curves [8]. These calibration curves are constructed for each CT scanner and its various scan protocols using real tissue composition data together with information of the X-ray energy spectrum.…”

Dosimetric Comparison of Pencil-Beam Scanning and Photon-Based Radiation Therapy as a Boost in Carcinoma of Cervix

“…Plans were generated for an IBA Proteus Plus system (IBA Proteus Plus, Ion Beam Applications, Louvain-La-Neuve, Belgium) using a universal nozzle. No range shifter was used due to the large (.10 cm) depth of the target [8][9][10].…”