Microdosimetric Measurements on the Clatterbridge Neutron Cancer Therapy Cyclotron

Abstract

Abstract Microdosimetric spectra have been measured both in air and in phantom for the Clatterbridge p(62)Be neutron cancer therapy cyclotron, Merseyside, UK. The measurements were carried out using a half-inch single-wire counter from Far West Technology, USA, for a simulated diameter of 2 µm. Because the measurements were made over several visits a rigorous calibration regime was used to ensure good agreement between spectra measured at different times. This was achieved by using the a particle edge on the y.D(y) spectra, the lineal energy of which was assumed to be 372 keV.µm-1. Measurements made at fixed positions in phantom show an increase in the height of the proton edge with increasing field sizes. Measurements made with fixed field sizes show a shifting of the proton peak to lower lineal energies with increasing depth into the water phantom, indicating a hardening of the neutron spectrum. This is consistent with spectrometric measurements made at Clatterbridge and reported elsewhere.