Air Kerma Calibration in Mammography of Thermoluminescence and Semiconductor Dosemeters against an Ionisation Chamber

Abstract

The ionisation chamber is often used as the reference dosemeter for dose measurements in radiology. Nevertheless it might be convenient for practical reasons to use thermoluminescence or semiconductor dosemeters as measurement dosemeters. A comparative study is presented using the main dosimetric properties of thermoluminescence and semiconductor dosemeters in mammographic X ray beams (molybdenum anode). The energy and air kerma responses are presented as well as the calibration procedure allowing transfer from the reference dosemeter to the measurement dosemeters. The ionisation chamber used was a plane parallel chamber model 96035B (Keithley, USA). It has been calibrated in terms of air kerma free-in-air at Nederland MeetInstitut for tube voltages between 20 and 35 kV in unattenuated beams. Thermoluminescence dosemeters are GR200A (material, LiF:Mg,Cu,P) and the semi-conductor is PMX3 (sensor ADI/8) and R100 detector from RTI. For both dosemeters, the energy response has been studied and entrance skin air kerma (ESAK) and entrance skin dose (ESD) performed with PMMA plates in order to validate the internal calibration procedure.