An ESR spectroscopic analysis of proton and photon irradiated bone

Electron spin resonance (ESR) spectroscopy was used to analyze the persistent free radicals in irradiated bone. Human cortical bone samples were irradiated in vitro by a 160-MeV proton beam and a 6-MV photon beam, and were subsequently analyzed with an x-band ESR spectrometer. The samples' spectroscopic g-values and microwave power saturation responses were studied, as well as various combinations of ESR signal peak-to-peak widths (PPW) and heights (PPH). The samples were also measured using the vector saturation transfer (VST) method, where first- and second-derivative ESR spectra collected at various modulation phases, and calculated third-derivative "harmonics," are compared. The samples' spectroscopic g-values and microwave power saturation responses were similar for both types of radiation. The g-values varied depending on bone dose and "background" signal, but became fairly regular around 50 Gy. The PPW were similar for both protons and photons, and varied with dose. The various groupings of PPH were all a linear function of dose. The ratio of net proton/photon PPH(dose) was 0.81, which differs from previous results. No significant differences were observed In the resultant VST harmonic figures, In conclusion, with the exception of the ratio of the net proton/photon PPH(dose), there were no significant differences in the spectroscopic character of the persistent free radicals in the proton- or photon-irradiated bone samples.