THE PRIMARY ATTENUATION COEFFICIENT OF A P(66)+BE(40) NEUTRON THERAPY BEAM

The concept of primary and scattered dose components of a radiotherapy beam is commonly used in radiotherapy planning. Four different methods which have been used for photon beams were applied to determine the primary dose linear attenuation coefficient in water (mu0) in a p(66)+Be(40) neutron therapy beam. They were: (a) the extrapolation of measured tissue-maximum ratios to zero field size, (b) linear attenuation measurements, (c) dose measurements in phantom with and without a central axis attenuator, and (d) fitting a central axis kerma model, based on convolution techniques, to measured percentage depth dose data. The mu0 values obtained agree well with each other and vary between 0.071 cm-1 and 0.075 cm-1.