Fiber-based dosimeter sensor adapted to proton-therapy
For many years, our group goes on developing sol-gel and MCVD-derived materials doped with active ions, devoted to ionizing radiation dosimetry. These silica-based glasses are made in the form of fibers or single small rods spliced to longer fibers for the purpose of transporting their light emission signals.
Several ionic dopants, like Cu+, Ce3+ or Gd3+, have shown ability to measure X-ray dose/dose rate by using their linear and efficient optical emission either through real-time radioluminescence or optically stimulated luminescence signals. This research topic on fibered dosimetry has led to collaborations with French partners through one ANDRA project (SURFIN) and one ANR project (FIDELIO), but also with a Canadian team at Triumf facility in Vancouver for proton-therapy aspects.
Optical fibers have the advantage of their size for accurate dosimetry in small fields, especially in proton-therapy, where the famous Bragg peak (BP) may be rather sharp. In this BP region, however, the scintillating materials composing the sensing fiber are usually limited by a signal quenching.
By comparing the response of several rods (with 0.5 mm-diameter and 10 mm-length) doped with different ions and fusion-spliced to a 5 m-long multimode silica fiber, we have shown that the Gd3+-doped material exhibits the best potential for dosimetry under 74 MeV proton beam, due to its very low signal quenching around the BP. Moreover, such a small sensor exhibits a favorable linear dose-rate dependency and a weak dependency on proton energy. In addition, the Gd3+-doped material exhibits a high sensitivity as well as a stable response after several proton irradiations.
Since this paper, thinner rod samples and even doped optical fibers have been achieved, opening doors to a better spatially resolved dosimetry at the BP.
References
[1] C. Hoehr et al., “Novel Gd3+-doped silica-based optical fiber material for dosimetry in proton therapy”, Scientific Reports 9:16376 (2019)
[2] C. Hoehr et al., “Optical Fibers for Dosimetry in External Beam Therapy”, Optical Sensors, Washington (2020), OSA Technical Digest (Optica Publishing Group, 2020), paper STu5D.2
[3] H. El Hamzaoui et al. “Gd3+-doped sol-gel silica glass for remote ionizing radiation dosimetry”, OSA Continuum 2, 715 (2019)