Feasibility study for the use of cerium-doped silica fibres in proton therapy

A radioluminescent (RL) dosimeter based on cerium-doped silica optical fibre was recently developed by means of the sol-gel and powder-in-tube techniques. The detector, already tested with both soft X-rays and more energetic photon beams used in conventional radiation therapy and in stereotactic radiosurgery, showed interesting and promising properties. A feasibility study for the use of the doped fibre in proton therapy is here presented. The measurements were performed at the proton therapy facility of the Paul Scherrer Institute (PSI) using a 138 MeV scanned proton pencil beam. The preliminary results showed a good sensitivity of the RL dosimeter to proton beams and a satisfactory reproducibility of the response (better than 0.5%) following repeated irradiations under the same experimental conditions. A linear dose response of the signal was observed in the investigated range (0.1–10 Gy) and, moreover, the stem effect proved to be negligible. The characteristic of the system to enable a real-time measurement of the dose rate was exploited for time-resolving different spot scanning sequences. Finally, the detector was used for assessing the depth dose curve in water: by comparing the curve obtained with the doped fibre with the corresponding one measured with a standard ionization chamber, a quenching effect in the order of 12% in the region of the Bragg peak was observed, as consequence of the decrease of the scintillation efficiency with increasing the Linear Energy Transfer (LET) of protons.