Sci—Thur PM: YIS — 06: Presentation of a Novel Scintillating Fiber Fluence Monitor for the Real‐Time Verification of Advanced MLC‐Driven Radiotherapy Treatment

Abstract

Purpose: To present a novel type of fluence monitoring detector based on optical attenuation for the on‐line quality control of radiotherapy treatments. Method: Long scintillating fibers were aligned along the direction of motion under each of the leaf pair of a Varian Clinac iX MLC and coupled on both ends to clear optical fibers to enable light collection. Following a theoretical model of scintillation collection based on optical attenuation, the detector performance was evaluated by 1) measuring the intrinsic variation of the readings, 2) comparing the experimental data to the expected values calculated from the treatment planning software (TPS) and 3) measuring random leaf errors introduced in an IMRT field. Results: The detector allows the measurement of the central position of the dose deposition on each fiber (xc) and the integral fluence passing through it (Φint). Very low intrinsic dispersion, dominated by Poisson statistics, was observed (under 1mm for xc and under 0.15% for Φint). When compared to the TPS, both xc and Φint) exhibited more significant deviations (respectively a mean of 1.3mm and 2.6%) due to the uncertainties on the dose calculated in regions of high perpendicular dose gradients.Φint is highly sensitive to single leaf motion errors as low as 1mm (at isocenter) while xc showed a good response to a leaf pair translation error of 2mm and more. Conclusion: This work clearly demonstrates the sensitivity and specificity of on‐line quality control of the incident fluence by a thin transmission detector based on optical attenuation of scintillating fibers.