Irradiation with x-rays of the energy 18 MV induces radioactivity in transfusion blood: Proposal of a safe method using 6 MV

Purpose: To prevent a fatal transfusion-associated graft-versus-host disease, it is recommended to irradiate transfusion blood and blood components with ionizing radiation. Using x-rays from a linear accelerator of the radiotherapy department is an accepted alternative to gamma irradiation devices of the blood bank and to the orthovoltage units that are replacing the gamma irradiators today. However, the use of high energy x-rays may carry a potential risk of induced radioactivity. The objective of this study was to investigate the effect of two different energy levels, 6 and 18 MV, which are executed in routine clinical settings. The research question was if induced radioactivity occurs at one of these standard energy levels. The authors aimed to give a proposal for a blood irradiation procedure that certainly avoids induced radioactivity. Methods: For this study, the authors developed a blood bag phantom, irradiated it with x-ray energies of 6 and 18 MV, and measured the induced radioactivity in a well counter. Thereafter, the same irradiation and measuring procedure was performed with a unit of packed red blood cells. A feasible clinical procedure was developed using 6 MV and an acrylic box. With the irradiation planning system XiO, the authors generated an irradiation protocol for the linear accelerator Siemens ONCOR Anvant-Garde. Results: Both measurement setups showed that there was induced radioactivity for 18 MV but not for 6 MV. The induced radioactivity for 18 MV was up to 190 times the background. This is significant and of clinical relevance especially since there are newborn and fetal blood recipients for whom every radiation exposure has to be strictly avoided. Conclusions: The irradiation of blood with x-rays from a linear accelerator of the radiotherapy department is safe and feasible, but by the current state of scientific knowledge, the authors recommend to use an x-ray energy of 6 MV or less to avoid induced radioactivity in transfusion blood.