Validation of blood product irradiation doses

Dosimetry of blood irradiation using x-ray beams on a medical linear accele rator has been studied to evaluate the accuracy of a diode detector and the delivery achievable. Variations in applied doses for a standard dual field 6 MV x-ray are measured with a commercial diode detector. Results show tha t the diode detector measured applied in vitro doses to within 5.4% (2 stan dard deviations (2 SD)) of those calculated with a collapsed-cone convoluti on treatment-planning computer for a sample of 100 blood irradiations. Expe riments involving the packing procedure of the blood products in the blood box were performed. It was found that a large proportion of the variation i n the predicted and measured dose was due to the compacting of the scatter material at the base of the blood box (over a 6 month period) producing a h igher density below the blood than originally scanned; hence an overall red uction of delivered dose was observed. The diode measurements (Which provid e an immediate printout) are recommended in conjunction with a film dosimet er such as radiochromic film, which still provides a back-up dose monitor a nd a visual reminder that the blood has been irradiated. It is also recomme nded that the blood box be completely evacuated of all scatter material eve ry month and the base be carefully repacked to provide uniform scatter mate rial.