Validation of Radiation Dose Received by Frozen Unprocessed and Processed Bone during Terminal Sterilisation

Abstract

Fresh frozen femoral heads (FH) and frozen processed bone (FP) are widely used as a source of allograft bone. The FP bone and some of the FH are terminally sterilised by the National Blood Service Tissue Services (NSBTS), via application of a minimum 25 kGy gamma radiation dose. To comply with the Guidelines for the Blood Transfusion Services in the United Kingdom (2002), frozen musculoskeletal tissue must be maintained below -40 degrees C during storage and transit. In practice, NBSTS stores bone long-term in -80 degrees C freezers. During transport for irradiation, a temperature of circa -79 degrees C is maintained by packing the bone in dry ice. An evaluation of the radiation dose received by bone has previously been made via dosimeters located within the tissue and dry ice, however, some evidence suggests that low temperature can influence the accuracy of the dosimeter readings. The aim of this study was to determine the actual radiation dose received by FH and FP bone during the irradiation process. This was accomplished by comparing radiation dose readings from dosimeters placed in dry ice with dosimeters placed in a dry ice substitute of similar dimensions and density i.e., polytetrafluoroethylene (PTFE) at ambient temperature. New packing formats were developed for both FH and FP bone such that 15 FH or 3 kg of FP bone could be irradiated in one transport box at any given time in a standardised fashion. The data show that low temperature consistently increased dosimeter readings 10--27%, and that radiation dose always fell within the range of 25--40 kGy (FH=25.1--35.7 kGy; FP bone=25.2--32.4 kGy).

Performance of cooling materials and their composites in maintaining freezing temperature during irradiation and transportation of bone allografts

“…The duration covers the transport of the bones from the Bone Bank to the irradiation facility, sterilization process, and the transport of the irradiated bones back to the Bone Bank. By using 20 kg DI, the lowest initial temperature recorded was −77.1°C almost similar to the report by Eagle et al, 11 where low temperature of −79°C was obtained by 15 kg DI in a polystyrene.…”

“…4,[6][7][8][9] Hamer et al 10 found that femur rings irradiated at À78 C on DI were less brittle due to less collagen damage as compared to bones irradiated at room temperature. Eagle et al 11 kept tissues at a low temperature of À79 C in 15 kg DI in polystyrene-insulated transport boxes during the transport to and from the gamma facility. Rooney et al 5 used 2.5 kg DI to maintain À55 C for at least 48 h, while Russell et al 12 and Gut et al 9 used DI to maintain deep freezing temperature of À70 C and À50 C throughout irradiation process, respectively.…”

Impaction allografting in revision total hip replacement

“…20 Gamma irradiation (at least 25 kGy) can be used to sterilise whole femoral heads, or in combination with freeze-drying of smaller fragments of bone. 21 Gamma irradiation at clinically-relevant levels (25 kGy) has no effect on the mechanical properties of frozen unprocessed human cancellous bone 22 but irradiation at a higher dose of 60 kGy was found to reduce significantly the compressive failure stress and the elastic modulus. Irradiation at room temperature increases the damage to bone by free radicals released from water; these are more immobile when bone is irradiated in the frozen state.…”

Effect of low dose and moderate dose gamma irradiation on the mechanical properties of bone and soft tissue allografts

“…It is reported, however, that the temperature of dry ice has negative effects on dosimeters and may falsely increase the dose measured by at least 10% (Biramontri et al 1996;Eagle et al 2005). To compensate for this, and to ensure that an accurate dose is reported, a dose mapping validation was performed at ambient temperature with simulated dry ice, having similar size, shape, and density to dry ice.…”