Advanced Physics for Brachytherapy 2018

Chapter 5: Calibration at the SSDL and Hospital Level

5.5. Guidance on constancy limits for well type chambers Chamber output stability should be checked at least 4 times per year. If the calibration factor from 137 Cs re-calibrations, and periodic constancy checks, remain the same within 1% for high-energy photon sources, or within 1.5% for low-energy photon sources, it can reasonably be assumed that the calibration factor for other sources has not changed. Recalibration is recommended if it is observed that response changes by more than the limits given above. 5.6. Electrometer to be used IEC 60731 describes desired characteristics of electrometers. They also shall be capable of measuring up to 0.2 μA for HDR sources and have a signal resolution of 0.1%. For LDR sources, signal resolution should be < 10 fA or less; this may be achieved by charge resolution of 0.2 pC when used in charge integration mode. It may be necessary to have two electrometers to cover the full range of brachytherapy sources to be calibrated.