Paired Mg and Mg(B) ionization chambers for the measurement of boron neutron capture dose in neutron beams

The use of the boron neutron capture (BNC) reaction to provide a dose enhan cement in fast neutron therapy is currently under investigation at the Gers henson Radiation Oncology Center of Harper Hospital in Detroit, MI. The imp lementation of this treatment modality presents unique challenges in dosime try. In addition to the measurement of photon and neutron doses in the mixe d field, a measure of the thermal neutron flux and the associated boron neu tron capture dose throughout the treatment volume is desired. A pair of sma ll-volume magnesium ionization chambers has been constructed with the aim o f providing this information. One of the chambers, denoted the Mg(B) chambe r, is lined with a boron-loaded foil. The ionization response of this chamb er has been calibrated in terms of BNC dose per ppm loading of B-10. These paired chambers can be used to map the local BNC response in neutron beams. From this data and an estimation of the boron concentration in the tumor a nd normal tissue, the boron neutron capture enhancement may be evaluated. ( C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)0161 1-9].