An equivalent thermal neutron fluence detector for boron neutron capture therapy

A 6Li-filled neutron detector, placed at the tumour site, which integrates over the slowing down spectrum of neutrons in the same manner as the 10B contained in the tumour, appears to provide a practical method to measure the equivalent thermal neutron fluence in boron neutron capture therapy (BNCT). If the boron concentration of the blood, brain and tumour are known, then, with the detector measurement, the boron absorbed dose can be calculated for these tissues. A detector containing 0.01 mg of 6Li results in the production of an amount of 18F which produces a detected activity of 1.5 x 10-9 counts per second per n/cm2. This detector can measure the equivalent thermal neutron fluence with an accuracy of 1% for a single treatment fraction of 1012cm-2, corresponding to one-tenth of the total fluence to the tumour. The depression of the boron absorbed dose by a 0.25 cm radium spherical detector with a 6Li mass of 0.01 mg is approximately 0.15%, immediately adjacent to the detector. (author)