Optimization of intraoperative (IO) BNCT: pre-irradiation surgical technique and 2-D dosimetry in surgical field

In IOBNCT, pre-irradiation surgery and clinical dosimetry procedures, and the patient's head position toward the beam port are crucial in optimum beam delivery to the target area. From Oct. 1999, 5 patients with malignant glioma were treated with IOBNCT at JRR-4. 2 fronto-temporal craniotomies and 1 occipital craniotomy were performed. 2 temporal lesions were explored with fronto-temporo-zygomatic approach (FTZ). In irradiation with occipital craniotomy, superior sagittal sinus (SSS) lied adjacent to post-surgical cavity that unwillingly enhanced the dose at the SSS by void effect. For FTZ, we aimed to avoid insufficient dose delivery to the lower frontal and anterior temporal regions that were caused by relatively increased core-target distance due to reflected skin flap and LiF thermoplastic collimator. Two-dimensional thermal neutron flux distributions in post-surgical field were influenced by head position, void effect, and the shape of LiF thermoplastic collimator. A simple simulation method for IOBNCT has been developed which improved the pre-irradiation treatment planning. However, more sophisticated dose planning system combined with patient setting system should be developed. (author)