A gauge for measuring the dose rate and activity of ophthalmic applicators

A gauge was developed for determining the dose rate distribution and surface activity of ophthalmic brachytherapy applicators, particularly for 106Ru applicators. A plastic fi 2×2 mm scintillator is used as the radiation detector, featuring a high pulse count rate, which results in a low 0.5% random error, due to good counting statistics. Automatic gain control of the photomultiplier tube (PMT) is achieved using a LED as the reference light source. The PMT operates in pulse mode. Long term gain variation due to fatigue of the PMT or ambient temperature variation is thus compensated for. The count rate error due to inaccurate setting of the high voltage supply of the PMT is 0.4%, and the instability error over 7 hours of continuous operation does not exceed 1-2%, peak-to-peak.