Characterization of the field size dependence for collimator, peak scatter and relative dose factors

P. BELMAR, R. ELIAS, M. FUENZALIDA & M. VALENTE

Pucon

Congreso; Reuniçon Anual de Sociedad Chilena de Fisica SOCHIFI; 2010

Sociedad Chilena de Fisica SOCHIFI

Nowadays, radiotherapy is one of the main strategies for cancer disease treatment and control. Dierent radiations can be used for radiotherapy, howevehigh energy photons and electrons constitutes the more employed radiations foconventional radiation therapies.The accuracy and disease control capability are strongly dependent upontreatment radiation characterization. Actually, there are a lot of beam parameters that need to be carefully studied and determined in order to ensure that thconsidered radiation assesses all requirements regarding its clinical implementation. Collimator, peak scatter and relative dose factors are three of the mainphoton beam parameters that need to be determined, because they charcterizthe inuence of the eld size on the absorbed dose.This work presents a review of the analytical models and International Protocol (TRS-398) recommendations dedicated to the denition and assessmenof collimator factor (CF), peak scatter factor (PSF) and relative dose facto(RDF) by means of standard dosimetric techniques. In addition, dedicated fullstochastic subroutines (based on the PENELOPE v.2008 main code) have beendeveloped with the aim of peforming suitable Monte Carlo simulation capablof virtually determining the mentioned factors in typical clinical situations. Thresults obtained by means of Monte Carlo simulations have been compared withanalytical models available in literature showing very good agreements.