SU-E-T-139: Feasibility Study of Glass Dosimeter for in Vivo Measurement: Dosimetric Characterization and Clinical Application in Proton Beams.

PURPOSE To evaluate the suitability of the GD-301 glass dosimeter for use in in vivo dose verification in proton therapy. METHODS The glass dosimeter was analyzed for its dosimetric characteristic in proton beam. Dosimeters were calibrated in a water phantom using a stair-like holder specially designed for this study. To determine the accuracy of the glass dosimeter in proton dose measurements, we compared the glass dosimeter and TLD dose measurements of plan delivery using a cylindrical phantom. We investigated the feasibility of the glass dosimeter for the measurement of dose distributions near the superficial region for proton therapy plans with a varying separation between the target volume and the surface of 6 patients. RESULTS Uniformity was within 1.5%. The dose-response has a good linear. Dose-rate, fading, and energy dependence were found to be within 3%. The beam profile measured using the glass dosimeter was in good agreement with the profile obtained from the ionization chamber. Depth-dose distributions in non-modulated and modulated proton beams obtained with the glass dosimeter were estimated to be within 3%, which was lower than those with the ionization chamber. In the phantom study, the difference of isocenter dose between the delivery dose calculated by the Eclipse and that of the measured by the glass dosimeter was within 5%. In vivo dosimetry of patients, given the results of the glass dosimeter and TLD measurements, calculated doses on the surface of the patient are typically overestimated between 4% and 16%. CONCLUSIONS As such, it is recommended that bolus be added for these clinical cases. We also believe that the glass dosimeter has considerable potential to be used for in vivo patient proton dosimetry.