Numerical dosimetry of stereotactic radiosurgery treatments in pediatric patients

Brain and nervous system neoplasms account for 25 % of childhood cancer cases. In these instances, radiotherapy treatments increase survival rates, but the high radiosensitivity of pediatric patients raises concerns about the potential adverse effects of radiation. Thus, dose delivery precision becomes crucial in treatment planning, and stereotactic radiosurgeries, such as those performed with Gamma Knife equipment, are the leading-edge techniques in precision radiotherapy. This study aims to evaluate conversion coefficients for equivalent doses (CC[H_T]) for out-of-field organs using pediatric mesh-type reference computational phantoms aged 1-, 5 -, 10-, and 15-years during stereotactic radiosurgery through computational simulations with the MCNP 6.3.0 code. Higher CC[H_T] values were found for organs closer to the target organ of the treatment, such as the eyes, salivary glands, and thyroid, which received an average of 33.6 %, 6.4 %, and 2.6 % of the treatment dose, respectively. As the age of the pediatric phantom increased, CC[H_T] values in organs farther from the target region decreased due to the increase in body length. We also determined the conversion coefficients for effective doses CC[E] and observed higher CC[E] values for the computational phantom with the lowest BMI. Thus, computational simulations showed to be meaningful tool for estimating out-of-field CC[H_T] values in pediatric patients and CC[E] values, given the challenges of performing organ-level dosimetry.