Development of a shielding to protect patients against photoneutrons produced by linacs in radiotherapy treatments

This work focused on radiological protection of patients submitted to radiotherapy using high energy linear accelerators, in which their healthy tissues receive undesirable doses due to photoneutrons. For that, a shield against the produced photoneutrons was developed using the computer code Monte Carlo N-Particle version X (MCNP-X). This shield showed to be positioned in a simple way, at the outside part of the linear accelerator's head, reducing the doses. This shield was named external shielding. The simulation was performed using a computational model of the head of a Varian 2300 C/D linear accelerator, plus the external shield. In order to verify the effects of this shielding, the values of ambient dose equivalent were calculated. These values were compared with the accelerator operating with and without the external shielding. The results of this study indicated that the external shielding showed great efficiency in reducing the ambient dose equivalent due to photoneutron, resulting in an average reduction above 60% for the various simulated configuration, without increasing the ambient dose equivalent due to the photos at the plane of the patient. It was concluded that the implementation of an external shield at the accelerator's head increases the protection of the patients against undesirable photoneutrons doses and may avoid new focus of cancer produced by the radiotherapy. (author)