Differences among doses for neuro-axis radiotherapy planning in the gonadal region

Radiotherapy can disrupt the functioning of the hypothalamic-pituitary axis, directly causing ovarian deficiencies, such as the decrease in fertility or damage that renders the uterus incapable of accommodating the growth of a fetus. However, these issues have become increasingly important to a growing number of pediatric and adolescent cancer survivors. The whole-body, cranial-spinal axis, as well as abdomen and pelvic region irradiations may expose the ovaries to radiation and may cause premature ovarian failure, whereas doses above 35 Gy cranial can affect the hypothalamic-pituitary functions. This study performed a comparison of four doses of radiotherapy planning techniques for the neural axis. For this analysis, technical simulations were performed for the treatment of medulloblastoma in four different planning, applied in a RANDO anthropomorphic phantom and dosimeters (TLD-100). The radiation fields in the 1”st and 2”nd planning were 40 x 5 cm”2 and 17 x 5 cm”2 with 4.0 cm depth, in which doses were 0.03 and 0.05 Gy / day and 0.11 and 0.09 Gy / days, on the right and left sides, respectively. The 3”rd and 4”th measured planning 32 x 7 cm”2 and 18 x 7 cm”2, with a 2 cm gap and a 4.0 and 5.0 cm depth, in which doses were 1.08 and 0.2 Gy/day and 1.14 and 0.14 Gy/day, on the left and right sides, respectively. It could be observed that the doses in the ovaries in the 3”rd and 4”th schedules proved to be larger than the doses in the 1^st and 2ⁿd planning. This is caused by the spinal field width and the depth of the second spinal field, which is 1.0 cm more than the field of the 1”st and 2”nd planning. These differences should be observed in image planning, as incorrect measures can cause damage in the treatment finish. (authors)