Neutron dosimetry intercomparisons between National Accelerator Centre, Université Catholique de Louvain and...

Neutron dosimetry intercomparison studies have been undertaken at three neutron therapy facilities which have similar beam characteristics; viz. National Accelerator Centre, South Africa [p(66 MeV)+Be], Université Catholique de Louvain, Belgium, [p(65 MeV)+Be] and MRC Cyclotron Unit, Clatterbridge Hospital, U. K. [p(62 MeV)+Be]. The procedures followed at all centres were the same: tissue equivalent (TE) ionization chambers were first calibrated in 60Co beams and then exposed under various conditions in the respective neutron therapy beams. Measurements were made with the chambers flushed with TE gas or filled with static air. The neutron beam measurements differed by a maximum of 2.4%, whereas if only one particular type of ionization chamber is considered the spread in values is reduced to +/- 0.5%. The TE gas/air response ratios are consistent with calculated values. The results obtained are highly satisfactory and confirm that the dosimetry procedures adopted by the participating institutes conform to international standards.