Estimativa do risco de câncer radioinduzido em pacientes pediátricos submetidos a radiografias de tórax via Simulacão Monte Carlo

Abstract

Chest radiographs are a fundamental diagnostic tool in any service equipped with a radiology department. As an efficient, quick, inexpensive, and non-invasive procedure, it is frequently employed as an initial examination to guide and often finalize the patient’s diagnosis. The exposure level for a patient undergoing a chest radiograph is on the order of a few μGy, which is insufficient to cause any deterministic tissue reactions, only stochastic effects. However, for pediatric patients, due to their high radiosensitivity, the probability of these stochastic effects is significantly higher. Considering this scenario, the primary objective of this study is to utilize Monte Carlo simulations to quantitatively assess these cancer induction risks, expressed as excess relative risk (ERR), for exposures during childhood. To achieve this objective, the MCNPX2.7.0 radiation transport code was selected. Virtual simulators provided in ICRP 143 were used, incorporated into an exposure scenario replicating a standard procedure room. The voltage values were selected based on age, ranging from 60 kV for newborns to 77 kV for 15-year-old adolescents. The Monte Carlo results were normalized by the entrance skin dose experimentally measured at Júlio Müller University Hospital. The findings confirmed the expected, that patients exposed at earlier life stages have a higher likelihood of developing cancer at advanced ages. Additionally, female simulators consistently exhibited higher ERR values, indicating greater radiosensitivity in females compared to males. The highest ERR value obtained was 59,43 × 10−5 for stomach cancer risk in the 15-year-old female simulator during adulthood, while the lowest values were below 1 × 10−5 for all ERR cases related to the prostate. These results suggest that for every 100.000 diagnosed cases, only a few dozen excess cases would be expected in the scenario of the highest ERR. Finally, this study concludes that, while the risks are low and the benefits to pediatric patients include rapid, accurate, and cost-effective diagnosis, any recommendations for practices involving ionizing radiation for healthcare purposes should ultimately be determined by the physician responsible for the patient.