Cuantificación de la dosis en superficie en radioterapia: Simulación Monte Carlo y medidas con cámara de extrapolación

Abstract

During a radiotherapy treatment, skin of the patient is always exposed to the radiation;

as a consequence late effects can be appear. Therefore, dose values in this region may be of interest for clinical evaluation and investigation of those undesirable effects.

However, surface dose is not intuitive and is difficult to measure and calculate; the parameters, which modify it are not always the same and each one are dependent to the others. The aim of this project is to quantify absorbed dose in the build-up region and near to the skin approximately between 0 mm - 1 mm using two methods. One of them,

an analytical calculation using Monte Carlo simulations; and the other an experimental

approach using an extrapolation chamber.

Monte Carlo simulations are performed with the PENELOPE package of subroutines

for 6MV and 15MV photon beams. Experimental setup consists in the use of an extrapolation chamber (PTW model 23392), considered the most suitable instrument to

measure absorbed dose in the build-up region, but its not commonly available in the

hospitals because its use is not practical. The chamber was adapted for its use in clinical

environments in a previous work, then for this work the measurement process is easier

and results with high level of accuracy can be obtained.

In this way, EC (extrapolation chamber) measurements served as the gold standard in

our study to validate the Monte Carlo simulations and also with results reported by

previous studies. As a result, we found that simulation outcomes are in good agreement

with experimental data.