Spectral measurements and Monte Carlo calculations of scattered radiation from therapeutic radiation sources

Selective shielding of a p-Si detector for quality independence

p-silicon semiconductor detectors were partially shielded with lead filters of various geometries with the purpose to minimize the quality dependence in assessments of depth dose distributions in large fields of cobalt radiation. It is shown that a lead shielding of the detector, with the front side excluded, reduced the signal error from about 3 to less than one per cent of the maximum signal as compared with an ionization chamber. Shielding was also done by encapsulating the detector in a mixture of wolfram powder and epoxy resin, with similar results. The signal received at the surface was not affected by this filter geometry. The directional dependence was investigated and was far from uniform for the wolfram-shielded detector. This will however not cause any practical problems when the detector is oriented towards the radiation source.

Measurements of single event spectra with a wall-less proportional counter in low LET radiation fields

Measurements have been made on 60Co gamma rays from a point source and on 6 MV roentgen rays from a linear accelerator with a wall-less proportional counter. Single event spectra have been measured in sites of 0.5-2 mum in diameters stimulated with a tissue equivalent gas. Calculations of the relative variance in LET are performed and compared with the relative variance of the measured distributions for estimates about the straggling contribution.