Analysis of the calibration results of ionization chambers for orthovoltage and brachytherapy

An analysis of the exposure calibration coefficients for ionization chambers used for dose determination in orthovoltage radiotherapy and in brachytherapy in the Polish SSDL was performed. The coefficients were determined by calibrating the chambers in the X-ray beam of 235 kV or 290 kV and HVL of 2.5 mmCu or 4 mmCu respectively, and also in the Co-60 gamma beam. Calibration procedures followed IAEA recommendations in Report No. TECDOC 1274 and Technical Reports Series No. 277. The characteristics of the energy dependence of various types of chambers used in orthovoltage radiotherapy and in brachytherapy are presented. On the basis of the summarized data and on the energy dependence curves it was possible to conclude that: 1) in he case of calibration of the chambers for orthovoltage radiotherapy the energy dependence has to be established for the full range beam qualities; 2) in the case of calibration, of the investigated chambers, for brahytherapy with Cs-137 and Ir-192 sources, establishing of the exposure calibration factor for Co-60 is sufficient.