Neutron dosimetry intercomparison between Clatterbridge and NAC (Pretoria)

An intercomparison of TE chamber responses was undertaken by measuring the total absorbed dose at different depths in a water phantom exposed to the p(65) + Be neutron therapy beam of the MRC Cyclotron at Clatterbridge (UK). The NAC (Pretoria) ionization chamber used in these measurements was calibrated at Clatterbridge using the hospital reference standard. Clatterbridge TE gas and instrumentation were used throughout. To monitor differences in electrometer responses, a pA current source was used to relate the responses of the Clatterbridge and Pretoria electrometers. Differences in the composition of the TE gas mixtures used at the two centres were quantified by means of measurements with and without TE gas. After applying the physical constants proposed in a supplement to the European and American protocols for neutron dosimetry, good agreement for the measured total absorbed dose was obtained