Non-invasive determination of the irradiation dose in fingers using low-frequency EPR

Several reports in the literature have described the effects of radiation in workers who exposed their fingers to intense radioactive sources. The radiation injuries occurring after local exposure to a high dose (20 to 100 Gy) could lead to the need for amputation. Follow-up of victims needs to be more rational with a precise knowledge of the irradiated area that risks tissue degradation and necrosis. It has been described previously that X-band electron paramagnetic resonance (EPR) spectroscopy could be used to assess the dose in irradiated amputated fingers. Here, we propose the use of low-frequency EPR spectroscopy to evaluate non-invasively the absorbed dose. Low-frequency microwaves are indeed less absorbed by water and penetrate more deeply into living material (approximately 10 mm in tissues using 1 GHz spectrometers). This work presents preliminary results obtained with baboon and human fingers compared with human dry phalanxes placed inside a surface-coil resonator. The EPR signal increased linearly with the dose. The ratio of the slopes of the dry bone to whole finger linear regression lines was around 5. The detection limit achievable with the present spectrometer and resonator is around 60 Gy, which is well within the range of accidentally exposed fingers. It is likely that the detection limit could be improved in the future, thanks to further technical spectrometer and resonator developments as well as to appropriate spectrum deconvolution into native and dosimetric signals.