Room: ePoster Forums
Purpose: In order to measure doses in small-field proton therapy, as for example in the treatment of choroidal melanomas, small detectors with superior spatial resolution are needed. Optical fibers are ideal except for the quenching in the high LET region of the Bragg peak, which causes the deposited dose to be severely underestimated. To overcome this problem, we manufactured several different doped silica-based fibers at the PhLAM Laboratory of the University of Lille, France, and tested them at the Proton Therapy facility at TRIUMF, Canada. To estimate the behavior in the secondary neutron fields routinely present at proton therapy facilities, we also tested the fibersâ€™ response with neutrons.
Methods: Novel silica-based fibers of 0.5 mm diameter were manufactured via the sol-gel technique and doped with copper, cerium or gadolinium. The GdÂ³â?º concentration was 0.1 wt%, while for CeÂ³â?º and Cuâ?º it was 0.07 wt%. The fibers were then irradiated at the clinical Proton Irradiation Facility (PIF) and at the TRIUMF Neutron Facility (TNF) to determine radiation-induced luminescence (RIL) under proton (63 MeV) and neutron (400 MeV to thermal) irradiation. Under proton bombardment, dose-rate dependence and energy dependence, or quenching, were also investigated.
Results: Both the CeÂ³â?º- and Cuâ?º-doped fibers had similar light output for neutrons and protons, respectively; both also experienced significant quenching in the Bragg peak. While the GdÂ³â?º-doped fiber had the lowest RIL with neutrons, it exhibited the highest RIL with protons. In addition, with the GdÂ³â?º-doped fiber quenching was greatly reduced. We attribute this to the unique electronic configuration and consequent energy levels in GdÂ³â?º.
Conclusion: We have identified a unique silica-based fiber that experiences reduced quenching in high LET irradiations, making it an ideal detector for small-field proton therapy dosimetry.