Análise de variação de dose em campos pequenos de aceleradores lineares

Abstract

Radiotherapy is a crucial technique in the treatment of cancers, often combined with other therapeutic approaches such as chemotherapy and immunotherapy. Radiotherapy with linear accelerators uses beams of electrons and X-photons to eliminate or contain the growth of tumor cells. The advancement of radiotherapy technologies demands more dynamic planning to meet the individual needs of patients. In innovative modalities, such as stereotactic radiosurgery (SRS), stereotactic body radiotherapy (SBRT), increasingly smaller fields, known as small fields, are used, often smaller than 4x4 cm², until now still an uncertain field size in the literature. However, dosimetric analysis for these fields faces challenges due to electronic imbalance, source obstruction, high dose gradients, and small detector sizes. In 2006, the International Atomic Energy Agency recorded accidents related to small fields due to problems in acquiring dosimetric data from linear accelerators. Errors in planning calculations resulted in higher than planned doses for patients, highlighting the importance of accurate determination of dosimetric data, appropriate selection of detectors, and rigorous evaluation of computerized planning systems. This work presents a dosimetric analysis of small fields (1x1 cm², 2x2 cm², 3x3 cm²) and conventional fields used in radiotherapy treatments, such as fields of 5x5 cm² and 10x10 cm² in two different linear accelerators, using Gafchromic EBT3 radiochromic film, in a solid water simulator, with the aim of investigating dose variations in different field sizes. Irradiations were carried out in axial and longitudinal fields.