Chemical dosimetry using an iodide/iodate aqueous solution: application to the gamma irradiation of blood

A method is presented for measuring and verifying the radiation dose in gamma irradiators used for treating blood prior to transfusion. This method employs the iodide/iodate dosimeter (0.6 M iodide, 0.1 M iodate, and 0.01 borate at pH 9.25) which forms triiodide upon exposure to ionizing radiation; for Cs-137 radiation the G value is 14.1. Samples were placed in a canister and irradiated in a conventional blood bank irradiator containing several Cs-137 sources. The following were exposed: (a) nine 1.5 ml plastic tubes containing dosimetry solution taped inside a 250 ml blood bag, which, in turn, was filled with either water or blood, (b) 50 ml plastic syringes containing varying amounts of dosimetry solution, (c) a whole blood bag containing 250 ml of the dosimetry solution. A water phantom was not used during exposure. The absorbance changes at 352 nm due to triiodide formation were used to determine a dose rate, which was on the order of 10 Gy/min (±5%) for all samples measured. This value is consistent with an average time-decayed dose rate for the irradiation volume as determined from the manufacturers calibration of the unit taking into account the heterogeneous nature of the radiation field inside the irradiator and the absence of a water phantom. Because of its sensitivity, ease of operation, and reproducibility, it is suggested that the iodide/iodate dosimetry system be considered for on-site periodic conformation/verification of the radiation dose as part of a quality assurance requirement for blood irradiators.