Avaliação de dose superficial devido ao uso de máscaras termoplásticas de cabeça e pescoço em radioterapia

Abstract

Radiotherapy is a modality for treatment that uses ionizing radiation aiming to annihilate or reduce the tumoral cells, preventing them from spreading and complicating the patient’s cure, among others. The radiation ministered to the patient have the energy in mega electron-volts that can damage the healthy cells. Therefore, the dosimetry performs an important role in the procedures, determining the radiation dose that reaches patients undergoing radiotherapy treatment. The objective of this work was to evaluate of the increasing doses reaching the patient’s skin, in procedure using the head and neck thermoplastic masks, which helps in the positioning, avoiding movements and helps in the reproducibility of the treatment, besides presenting means for a reduction of such dose. In an anthropomorphic simulator (phantom), two different thickness thermoplastic masks were molded. Over the phantom, TL detectors were placed in areas sensitive to the human body, and then exposures were performed on a linear accelerator with 6 MV photon beams of the Synergy Elekta brand, with and without the use of the thermoplastic masks. An increase in the doses penetrating the skin was obtained with the use of the thermoplastic masks. In some areas, such as the crystalline, the percentage of difference has reached almost 200%, while in some other areas, such as the thyroid, brain, and parotid, have a decreasing percentage, indicating a dose attenuation entering the skin by the use of an immobilizing device. Variables such as the thickness and diameter of the device holes affect the dose delivered to the patient. Since the masks are essential for carrying out the treatment in radiotherapy, a plausible solution, for radiological protection of radiotherapy patients, is reducing the thickness of the thermoplastic material, while maintaining its hardness for immobilization and its holes with a larger diameter só that the beam incidence site remains free of material, thus minimizing the influence of thermoplastic masks on surface doses.