Avaliação de dose periférica em equipamentos de radioterapia com feixes de fótons de diferentes energias

Abstract

Nowadays, the most used equipment for radiotherapy are linear accelerators, that can employ both photon and electrons beams in the megavoltage range for cancer treatments. Although radiotherapy planning minimizes the doses received by adjacent and radiosensitive tissues outside the region to be treated, in the literature is reported that the peripheral doses received during the treatment application depends on the machine settings and the technique used, in addition to the anatomy of the patient. Considering the radiological protection of cancer patients and the mitigation of the biological effects of ionizing radiation, this study aimed to quantify the peripheral doses received in simulated treatment employing different energy of photon from the same equipment and considering photon beam with the same energy from different equipment. The irradiations were carried out in two linear accelerators (model CL600CD and Model CL2100). For the evaluation of the dose, thermoluminescent detectors of lithium fluoride doped with magnesium and titanium (LiF: Mg, Ti), commercially available as TLD100, were calibrated for each equipment and energy. The peripheral dose was evaluated by irradiating an adult anthropomorphic phantom (Alderson Radiation Therapy Phantom – ART-210) in which the TLD100 detectors were inserted or positioned in different regions of the simulator (right and left crystalline, thyroid, left breast, abdomen and gonads). In planning, the isocenter was positioned in the head, exposing to 20 Gy using 6 MV photon beams from different accelerator equipment and 6 and 15 MV photon beams from the same accelerator equipment. In all irradiations, the same size of field (5 x 5 cm²) and the same dose in the isocenter. It was observed that the more distant from isocenter, the lower the peripheral dose. We observed experimentally that, even using relatively small field size, there is a difference into the peripheral dose of up 275% in the abdomen region, when considering 6MV photons from different accelerator equipment.