Background: Given the increasing need for the use of ionizing radiation during pregnancy, the increase in the incidence of radiation therapy-related cancers has received attention. This study aims to determine the fetal dose resulting from whole-brain radiation therapy using two methods: a cobalt-60 treatment machine and a linear accelerator.
Methods: Using the Alderson RANDO phantom, after performing the calibration of TLD-100 chips, the fetal dose at weeks 12, 24, and 36 of pregnancy was evaluated based on the distance from the primary treatment field. The total brain radiation with therapeutic lateral opposing fields was delivered parallel to the phantom in a supine position. The treatment technique was carried out at SSDs of 100 cm and 80 cm for the linear accelerator and cobalt machine, respectively. The absorbed dose was measured using a TLD reader.
Findings: He mean radiation dose in an unshielded conceptus at gestational ages of 12, 24, and 36 weeks were about 926 ± 47, 2160 ± 125 and 6372 ± 498 micro Gy for Cobalt-60 gamma rays and 4559 ± 207, 6005 ± 260 and 6383 ± 228 micro Gy for 9 MV X-rays from linear accelerator.
Conclusion: Dosimetric results indicate that most of the dose from internal scatter radiation in the mother's body comes from scatter, and protecting the abdomen can only be partially effective. As the fetal age increases, the received dose varies significantly. Therefore, it is better not to rely on the average dose when assessing fetal dose, and the fetal dose should be estimated based on its maximum age.