The Dosimetry Calculation for Boron Neutron Capture Therapy

Abstract

BNCT incorporates the targeting principles of chemotherapy and the anatomical localization principles of conventional radiotherapy but with three distinct advantages:  Current boron compounds at the required concentrations are non-toxic.  The time interval between drug administration and neutron irradiation can be chosen to maximize the concentration differential between tumour and normal tissue.  Only the tissues located around the tumour volume are exposed to significant neutron activated boron damage. Following the earliest suggestions that BNCT might be useful for the treatment of human cancers, interest developed regarding the application of BNCT to primary high-grade brain tumours — glioblastoma multiforme (GBM). It was postulated that the reduction of the blood brain barrier (BBB) in the vicinity of tumour could be exploited to selectively increase the concentration of boron in the brain tumour over normal brain. Initially sodium tetraborate (borax), was used as the vehicle for boron. Perhaps the early interest in applying BNCT to high-grade primary brain tumours stemmed from the fact that this was a cancer with a very poor prognosis. This would ensure that BNCT, even if minimally successful, would nevertheless appear superior to ineffective conventional therapies. In addition to the considerations of beam quality, the beam should also be sufficiently intense to ensure that treatment times remain within reasonable limits. This facilitates the procedure for the patient and reduces the problem of patient motion during treatment. It should be realized that whereas conventional radiotherapy fractions are administered within a period of about 10 minutes, current clinical BNCT treatments often extend to a few hours per fraction (2001)[1]. In order for BNCT to be successful, a sufficient amount of 10B must be selectively delivered to the tumor (~20g/g weight or ~109 atoms/cell), and enough thermal neutrons must be absorbed by them to sustain a lethal 10B(n,)7Li capture reaction. Since the high linear energy transfer (LET) particles have limited boron pathlengths in tissue (5-9m), the destructive effects of these high energy particles are limited to cells containing boron. Clinical interest in BNCT has focused primmarily on the treatment of high grade gliomas, and either cutaneous primaries or cerebral metastases of melanoma, and most recently head, neck and liver cancer. Since BNCT is a biologically rather than physically targeted type of radiation treatment, the potential exists to destroy tumor cells dispersed in the