Experimental verification of a methodology for Monte Carlo modeling of multileaf collimators using the code Geant4

Alex Cristóvão Holanda De Oliveira,Miriam Zarza Moreno,José Wilson Vieira,Fernando Roberto Andrade Lima

doi:10.15392/bjrs.v6i2.324

Abstract

Among the many algorithms developed for evaluation of dose distributions in radiotherapy, the Monte Carlo methods provide more realistic results. In intensity modulated radiation therapy, significant differences in dose distributions within the fields defined by the multileaf collimator (MLC) could have significant radiobiology effects. Thus, it is important to model thoroughly the MLC to allow more accurate radiotherapy delivery. The objective of this work is to describe and to validate a methodology for modeling of MLCs using code Geant4. The Varian Millennium 120-leaf MLC was modeled using this methodology and it was experimentally verified. The leaves of the MLC were built using three types of solid (G4Box, G4Tubs and G4ExtrudeSolid) and the Boolean operation of subtraction (G4SubtractionSolid). Based on this methodology, it is possible to simulate other Varian MLC models using Geant4 or other MC code.

Highlights

Radiotherapy uses different techniques and equipment for treatment of cancer
The equipment most often used in radiotherapy is linear accelerator (Linac) which produces electron or X-ray beams in the energy range of 5 to 30 MeV (LOVEROCK, 2007)
Among the many algorithms developed for evaluation of dose distributions of radiation, the simulations based on Monte Carlo (MC) methods provide more realistic results (VERHAEGEN, 2013)

Summary

Introduction

Radiotherapy uses different techniques and equipment for treatment of cancer. The equipment most often used in radiotherapy is linear accelerator (Linac) which produces electron or X-ray beams in the energy range of 5 to 30 MeV (LOVEROCK, 2007). In intensity modulated radiation therapy (IMRT), where complex intensity distributions are delivered using a multileaf collimator (MLC), an accurate MC modeling of the Linac and MLC is very important. Significant differences in dose distributions of IMRT fields could have significant radiobiology effects (VERHAEGEN; SEUNTJENS, 2003). The sides of the leaves are designed to have a kind of fit between them. This configuration is known as tongue-and-groove and has the objective to minimize the radiation transmitted between adjacent leaves (LOVEROCK, 2007). The most important dosimetric parameters are leakage, penumbra and tongue-and-groove (T&G) effect. The leakage refers to radiation that emerges through the air gaps between adjacent leaves (IAG – interleaf air gap) and transmitted through the leaf material. It is important to model thoroughly the MLC to allow more accurate radiotherapy planning

Objectives

Methods

Results

Conclusion