Materials and methods
glioma, tumor
ADULT BRAIN TUMOR, TUMOR, PRIMARY DISEASE, GERM CELL TUMORS, BRAIN, GLIOMA, MEDULLOBLASTOMA, LARGE CELL LYMPHOMA, COLD
All the study procedures involving human participants were conducted in accordance with the ethical standards of the institutional research committee, in compliance with the Declaration of Helsinki, and with the approval of the institutional review board (No. 04-03). This study was conducted as a retrospective study, and we obtained patient consent via the opt-out method using the hospital’s website. The patients were 24 consecutive patients with pediatric and young adult brain tumor patients who completed CSI between Feb 2019 and Mar 2021; age: 1–24 (median 10) years). Primary diseases were medulloblastoma: 18, germ cell tumors: 3, choroid plexus tumor: 1, undifferentiated large cell lymphoma: 1 and glioma: 1 patient. RayStation, version 7 or 9 (RaySearch Medical Laboratories, Stockholm, Sweden) was used for treatment planning. The CTV included whole brain and spinal canal. Planning target volume (PTV) was set to CTV + 3 mm in the brain and CTV + 6 mm in the spinal canal. The vertebral bodies were included in the PTV in 13 patients whose age was younger than 10. Treatment method was PSPT in 8 patients (Feb–Oct 2019) and IMPT in 16 patients (Jan 2020–Mar 2021). As the field size was 15 × 20 cm in our facility, it was not possible to irradiate the entire PTV with one irradiation field. Thus, the PTV were divided in the SI direction. The number of divisions varied dependent on patients’ height. Brain beam direction was two opposing left and right in six cases and two oblique posterolateral in two cases in PSPT, and two oblique posterolateral in all cases in IMPT. The direction of the spinal cord beam was one posterior beam in both PSPT and IMPT. To mitigate hot and cold spots at the field junction, two sets of plans with different levels of the field were used in PSPT. For the patients of IMPT, each irradiation field was joined by sharing a 7 cm junction area with a linear slope in the dose distribution. Robust setting was 1% of range uncertainty to the PTV in the brain and 4 mm to the superior and inferior direction with 1% of range uncertainty to the PTV in the spinal cord levels. Total irradiation dose of CSI was 18 Gray (relative biological effect) (Gy(RBE)): 3, 23.4 Gy(RBE): 17, 25.2 Gy(RBE): 2, 36 Gy(RBE): 2, all 1.8 Gy(RBE) daily. The dose constraint for CTV is between 90 and 105%, and the acceptable range is between 83 and 106%. In addition, we try as much as possible to keep the PTV dose constraint between 90 and 105%. Cases in which dose constraints cannot be met are determined on a case-by-case basis. Boost irradiation to the local region was performed in 23 of 24 patients. Neoadjuvant and concurrent chemotherapy was performed in 23 and 19 patients, respectively. Follow-up period was 17–44 (median 27) months as of Dec 2022.We investigated PTV dose stability. We conducted a simulation to reproduce the situation in which the irradiation fields moved by shifting the iso-center coordinates of the irradiation field of cervical and lumber spinal cord level (C and L levels) step by step on the treatment planning system. The C and L levels were shifted up to a maximum of 5 mm by 1 mm to the antero-posterior, lateral, and cranial–caudal directions, respectively. We calculated 5 parameters for the PTV: the maximum dose (where PTVThe data represent mean value and standard deviation. Unpaired 