Extracorporeal irradiation--novel use of a blood product irradiator

A Cs-137 blood product irradiator (BPI) is used for extracorporeal irradiation of bone grafts. For dose verification purposes two bone phantoms were constructed of plaster of Paris and irradiated in the BPI. The first was a hollow cylinder measuring 15 cm x 3.3 cm to simulate cortical bone, filled with paraffin wax to simulate yellow bone marrow. The second was a concave ellipse 11.5 cm x 9.5 cm x 2.5 cm to simulate a section of ilium. The absorbed dose was measured with radiochromic film in the phantoms and in water for comparison with the manufacturer's calibration certificate. The relative dose distribution in the bone phantoms was measured using Li-F thermoluminescent dosimeters and normalized to a reference point near the centre of each phantom. The doses measured in water matched the calibration certificate within 4%. The doses measured at the cylindrical and elliptical phantom reference points were 49.9 Gy and 52.3 Gy respectively, compared to the nominal dose of 50.0 Gy. The relative doses within the cylindrical phantom ranged from 88% to 100% along the central axis of the wax cylinder, from 89% to 100% along the plaster/wax interface, and from 90% to 103% along the outer surface of the plaster cylinder. The relative doses within the elliptical phantom ranged from 100% to 108% along the inside surface, from 99% to 107% along the outer surface, and from 98% to 103% through the centre of the plaster ellipse. These data agree well with the isodose plot provided by the manufacturer.