WE-E-AUD-06: Clinical Prototype of a Plastic Water-Equivalent Scintillating Fiber Dosimeter Matrix for IMRT QA Applications

Abstract

Purpose: To develop a clinical prototype of a plastic water-equivalent scintillating fiber dosimeter array for IMRT beam quality assurance (QA) applications. Method and Materials: A clinical prototype of a scintillating fiber dosimeter array has been developed. The system comprises twenty-nine (29) 1 mm diameter and 2 mm long (1,6 mm3) scintillating fiber detectors (BCF-12, Saint-Gobain, inc.) spaced 1 cm apart encapsulated in a Plastic Water (MedTec inc.) phantom. The detectors are coupled to clear non-scintillating transport fibers (BCF-98, Saint-Gobain, inc.) that collect scintillation photons and transport them to a color charge-coupled device (CCD) placed on the treatment table outside of the primary beam. A spectral discrimination technique is used to remove the Cerenkov radiation contaminating the scintillation signal. The CCD is encased in a custom designed, Cerrobend shielded aluminum carrying-case equipped with a custom-made optical fiber connector enabling reproducible removal and insertion of the fibers. Residual radiative noise on the CCD is removed with a post-processing algorithm. All dose points are processed simultaneously. Results: Open field crossplane profiles from 4×4 to 20×20 cm2 and a 10×10 cm2 depth-dose in Plastic Water are compared to ionization chamber (CC13, Wellhofer) measurements in water. The maximum in-field relative difference across all points and measurements is found to be 0.9% for profiles and 1.6 % for the depth dose. The standard deviation on the scintillation detector response is smaller than 1% in-field. The optical fiber connector insertion and removal is repeatable to within the measurement resolution (1%). This will allow for “hot swappable” detector modules. Conclusion: The scintillating fiber dosimeter array prototype is found to be accurate, precise and practical. The current system detector capacity exceeds 3500 measurement points per single irradiation. Such array detectors could find application for IMRT QA and general beam dosimetry monitoring measurements.