Sandra Hopkins Final Report.pdf - University of Surrey

Figure 29 : Intervention coronary exam dose distribution map5. Discussion5.1 Verification of Dose Area Product and Skin Dose Indicator CalibrationIt is understood that for the Siemens Axiom Artis there is an integral ionisation chamber which canbe calibrated by the service engineer if required. Siemens have a specified criteria of +/- 30%. Theskin dose indicator is derived from the same output data so it is expected that on one system the twocalibrations would be fairly similar. The Dose Area Product calibration was found to be within 10%so this was much better than that specified by manufacturers and gave assurance as to the accuracyof the patient dose audit carried out using this equipment. Some systems have been found to be lessaccurate. This can be due to differences in the method of calibration carried out by the manufacturerto that shown here. It is known that Siemens carry out a free in air measurement and that is themethod employed here. However, some manufacturers keep the patient table in the beam path whencarrying out this calibration and this needs to be taken into account.The skin dose indicator calibration was checked using more than one method.34