Radiological safety of medical devices sterilized with X-rays at 7.5 MeV

The induced radioactivity in medical devices when sterilized with 7.5 MeV X-rays has been investigated theoretically and verified by dedicated experiments. The experimental setup has been chosen to simulate closely the situation in a commercial irradiation facility. The purpose of this study is twofold: compare activation of medical devices with regulatory limits and evaluate corresponding dose exposure of persons in contact with those devices. Samples of medical devices, classified in several test groups, were located in a stack of low-density material at the position of the highest photoneutron fluence and irradiated to X-ray doses between 25 and 30 kGy. The induced activities were measured with high purity germanium (HPGe) gamma ray spectrometers. The X-rays were generated in a tantalum target using a 7.3 MeV electron beam with a narrow energy spread during the first experiment and with a broad energy spectrum for a second one. Results have been scaled to 50 kGy and compared with theoretical estimates. In addition, the radiation exposure of four categories of persons (logistics personnel in the irradiation facility, truck drivers, doctors and patients) has been calculated from the measured activities. The measured activities are higher than theoretical expectations but still below governmental regulations. The annual dose received by the person category with the highest exposure is about 1% of the worldwide average environmental exposure, and for other categories it is negligible. The paper concludes that provided some precautions are considered, sterilization with X-rays from 7.5 MeV electrons can be regarded safe from the standpoint of public health and personal safety