Radiation Biology Irradiator Dose Verification Survey

Interest in standardized dosimetry for radiobiological irradiators has expanded over the last decade. At a symposium held at NIST, "The Importance of Standardization of Dosimetry in Radiobiology", a set of 12 criteria necessary for adequate irradiation was developed by the authors. Here we report on our review of dosimetry methods from various peer-reviewed publications and found that none of them satisfied all 12 criteria set forth by the authors of the NIAD/NCI/NIST proceedings. The inadequate reporting of dosimetry methods in the literature raises questions regarding the accuracy of the dose delivered to animal test subjects and the resulting experimental results. For this reason, we investigated the level of accuracy of dose delivery in radiation biology studies. We performed an irradiator output verification study of 12 radiation biology laboratories (7 gamma and 5 X-ray units) using polymethyl methacrylate (PMMA) mouse phantoms and thermoluminescent dosimeters (TLDs) readouts at the University of Wisconsin Medical Radiation Research Center (UWMRRC). The laboratories housing each of these irradiators were asked to deliver specific doses to individual mouse phantoms. Simultaneously, mouse phantoms at the UWMRRC were irradiated with NIST-traceable reference beams representative of the subject laboratories' beam energies. The irradiated mouse phantoms were returned from the various institutions to the UWMRRC and the TLDs were processed, with their measured dose response compared to the known dose response of the calibration phantom TLDs. Of the five facilities using X-ray irradiators, only one delivered an output within 5% of the target dose. The dose differences for the other four X-ray irradiators ranged from 12 to 42%. These results indicate the potential need for standardization of dose determination and additional oversight of radiobiology investigations.