Simulação Monte Carlo em irradiação de corpo inteiro: validação de feixe clínico e avaliação dosimétrica em objetos antropomórficos virtuais adulto e infantil

Abstract

Radiotherapy plays a pivotal role in the management of cancer and is indicated for a substantial proportion of patients, with curative, adjuvant, or palliative intent. Among its applications, Total Body Irradiation (TBI) stands out as an integral component of conditioning regimens for bone marrow transplantation, especially in patients with acute myeloid leukemia (AML). However, TBI presents specific dosimetric challenges related to the large extent of the irradiated volume, anatomical heterogeneity, and the need for dose homogeneity throughout the patient's body. In this context, the present study aimed to develop and validate, using the Monte Carlo (MC) method with the MCNP 6.3 code, a computational model of the 6 MV clinical beam from a VersaHD linear accelerator and apply it to the simulation of a TBI scenario with a long source to-surface distance (SSD). The dose distribution in adult and pediatric anthropomorphic MRCP mesh phantoms of both sexes, developed by the ICRP, was evaluated. The modeling included the implementation of a phase-space-based virtual source already described in the literature, as well as the geometric representation of the collimation system (MLC and backup jaws). Model validation was performed by comparing simulated results with experimental data, using percentage-depth dose (PDD) curves, beam profiles at different depths, and the TPR20,10 beam quality index. Agreement within clinically acceptable limits was observed, with percentage differences on the order of 3% for the reference field, 10 × 10 cm². After beam validation, the model was applied to the simulation of the TBI scenario, allowing the estimation of the absorbed dose in organs at risk and the comparison of the dose distribution between pediatric and adult models of the MRCP phantoms. The results show variations associated with anatomical and dimensional differences between the phantom objects, highlighting the importance of individualized approaches in dose estimation for each patient. It is concluded that the developed model demonstrated dosimetric robustness and clinical applicability, proving to be a reliable tool for dose distribution analysis in TBI and contributing to the improvement of the characterization of radiotherapy beams in complex scenarios.