Experience of Boron-neutron Capture Therapy for Malignant Brain Tumours — with Special Reference to the Problems of Postoperative CT Follow-ups

Summary

Boron-neutron capture therapy (BNCT) is theoretically a highly selective treatment of infiltrating tumours, in that the tumoricidal heavy particle radiation is limited to a sphere of 10 microns around a tumour cell which is loaded with non-radioactive boron-10 atoms.

There were 73 gliomas among the 83 cases treated by boronneutron capture therapy. For grade III–IV cerebral gliomas, 5 and 10 year survival rates were an unimpressive 19 and 10% respectively. This was the result of technical problems such as unsatisfactory reactors and inadequate craniotomies for the majority of the patients. If the analysis was limited to those whose tumours had been irradiated with more than 2.5 × 10¹² neutrons/cm² (yielding more than 3,000 rem or more), the 5 and 10 year survival were almost 100 and 50%. The longest surviving glioblastoma (grade IV) patient has lived in a satisfactory manner for the past 15 years. For the cases who had been treated with borderline doses (lethal or sublethal), interpretation of the postoperative CTs was frequently intriguing. Several cases had to undergo re-opening and occasionally even another BNCT, only to find no viable tumour tissue. Death occurred in some, either due to discontinuation of supportive treatments by local physicians, or due to excessive therapies by the author directly involved in the patient’s care, both of whom had erroneously believed in recurrence. At autopsy, residual tumour cells were recognized only in the areas where the above-mentioned neutron fluence had not been delivered at the time of the treatment. Delayed cerebral necrosis was not recognized except for the cases which had purposely been given a larger neutron dose than the current regimen.

If a larger reactor like those at MIT or Brookhaven of 1951–61 series is available, and if epithermal neutron facility is constructed, any deep-seated tumours will be good targets of BNCT. Application of larger diameter craniotomy and heavy water to replace the water in the cranial space will improve the thermal neutron penetration into deeper part of the brain, and will guarantee a better survival rate.