Evaluation of the effect of field sizes on radiation dose in the presence of metal materials using Monte Carlo simulation

The number of patients with implant materials requiring radiotherapy is increasing day by day. The purpose of this work is to investigate the effect of field size on dose distribution from a 6 MV flattening filter free (FFF) X-ray beam in the presence of stainless steel grade 316L (SS) and titanium alloy grade 5 (Ti5), which are the metals generally used in medical implants (dental implants, hip prosthesis etc.). This study compared also the Acuros XB (AXB) algorithm implemented within Eclipse treatment planning software (Varian Medical System, Palo Alto, CA) with Monte Carlo (MC) simulations with respect to field size in heterogeneous media. The percentage depth dose (PDD) curves were obtained for 6 MV FFF beam at three field sizes including 1 x 1, 3 x 3 and 10 x 10 cm2. The maximum dose increase was observed at 0.1 cm in front of both metal materials for all field sizes. The dose behind the metal material was affected by field size. The higher the Zeff of the metal material, the higher the dose observed. Beyond the metal materials, the maximum overestimated dose was seen in the case of 1 x 1 cm2 field size.