Boron neutron capture therapy using mixed epithermal and thermal neutron beams in patients with malignant glioma; Correlation between radiation dose and radiation injury and clinical outcome

Kageji, Teruyoshi*; Nagahiro, Shinji*; Matsuzaki, Kazuhito*; Mizobuchi, Yoshifumi*; Toi, Hiroyuki*; Nakagawa, Yoshinobu*; Kumada, Hiroaki

Clinical trials for boron neutron capture therapy (BNCT) for malignant glioma were performed with thermal-epithermal mixed neutron beam generated by JRR-4. The first protocol (P1998) prescribed a maximal gross tumor volume (GTV) dose of 15 Gy since 1998, and then the protocol was applied to 8 patients. In 2001, a dose-escalated protocol (P2001) was introduced, which prescribed a maximal vascular volume dose of 15 Gy, or alternatively, a clinical target volume (CTV) dose of 18 Gy, the protocol was applied to 11 patients. The GTV and CTV doses in P2001 were 1.1-1.3 times greater than those in P1998. The maximal vascular volume dose of those with acute radiation injury was 15.8 Gy. The mean GTV and CTV dose in long-term survivors with glioblastoma was 26.4 and 16.5 Gy, respectively. A statistically significant correlation between the GTV dose and median survival time was found. In the 11 glioblastoma patients in P2001, the median survival time was 19.5 months and 1- and 2-year survival rate was 60.6 % and 37.9 %, respectively. Dose escalation contributed to the improvement in clinical outcome. To avoid radiation injury, the maximal vascular volume dose should be 12 Gy. For long-term survival in patients with glioblastoma after boron neutron capture therapy, the optimal mean dose of the GTV and CTV was 26 and 16 Gy, respectively. This report introduces principle of BNCT and the activities for the BNCT clinical trials using JRR-4 in JAEA, and the clinical outcomes of the trials under the protocols and radiation injury in the irradiation are described.