The interpretation of dose calculations and cell-survival measurements for the boron neutron capture therapy of brain tumours with 24 keV neurons.

Monte-Carlo computer codes have been used to estimate the distribution of doses to borated and unborated tissues in head-sized phantoms when exposed to beams of 2 keV and 24 keV neutrons. For the application of such beams to boron neutron capture therapy (BNCT) these calculations show the superiority of 2 keV neutrons over 24 keV neutrons and the importance of using large-area beams. A 24 keV neutron beam has been used to irradiate HeLa cell cultures in vitro, with and without the addition of 10B, at various depths within a narrow polyethylene phantom. Survival data obtained from these experiments have been used to estimate depth-damage profiles for normal (unboronated) and tumour (boronated) brain tissues when exposed to 24 keV neutrons. A good differential between damage to normal and tumorous tissue is obtained under suitable irradiation conditions. Although lower-energy neutrons are probably preferable, these results demonstrate the possibility of using beams of 24 keV neutrons for the BNCT of brain tumours.