Dose verification by activation in vivo following proton beam eye radiotherapy

This work presents the measurements of proton activation of a group of 15 patients following proton radiotherapy of the eye. Despite the heterogeneity in activation response and reaction cross section compared with the applied uniform dose, it can be shown that induced activity may be related to incident fluence volume and thus provide verification of applied dose. This proton treatment provides in vivo information that is normally unused. Up to 400 kBq was measured at 100-second post-treatment. Significant correlation of the ¹⁵O 511 keV activity with fluence volume is shown. The patient γ-ray spectra are tabulated and discussed. The longer-lived ⁷Be (T _1/2 = 53.1 d) activity, from O and C activation, may provide an additional means of dose verification. The potential of (p,p’γ) reactions was examined by irradiation of phantoms. High energy γ-rays from O and C were measured with a large NaI(Tl) detector, with a yield of 125 γ/cm²/mGy for the ¹⁶O(p,p’γ) reaction.