Author: Louis Archambault, Luc Beaulieu, Alexis Horik, Sajjad Ahmad Khan 👨🔬
Affiliation: Département de Physique, de Génie Physique et D'optique, et Centre de Recherche sur le Cancer, Université Laval, Département de physique, de génie physique et d'optique, Université Laval 🌍
Purpose: This study presents a novel 2D scintillation dosimeter leveraging long scintillating fibers for quality assurance (QA) in radiotherapy. The primary goal is to optimize critical parameters such as the number of fibers, reconstruction algorithms, pitch, and projection angles. The device aims to provide real-time, non-rotative 2D dose mapping by stacking fibers in different orientations for accurate dose distribution.
Methods: A prototype dosimeter comprising 21 BCF-60 scintillating fibers (13 cm in length, spaced 0.5 cm apart) was evaluated using a 6 MV photon beam. Projection data were collected at angular intervals of 5°, 10°, and 20° from 0° to 180°. Reconstructions were performed for square and non-square fields using four algorithms: Simultaneous Iterative Reconstruction Technique (SIRT) + Total Variation (TV), Filtered Back Projection (FBP), Algebraic Reconstruction Technique (ART), and SIRT alone. Reconstruction quality was assessed using Structural Similarity Index Measure (SSIM), Mean Squared Error(MSE), Contrast-to-Noise Ratio (CNR), radiochromic film measurements of the same field.
Results: SIRT + TV outperformed other algorithms due to superior CNR and noise suppression. For square fields, 5° and 10° interval reconstructions produced consistent field sizes (8cm × 8cm) with high SSIM (0.98 for 10° vs. 5°). The 20° interval caused minor vertical distortion (8cm × 8.5cm) and slightly lower SSIM (0.96). CNR decreased from 15.8 (5°) to 11.5 (20°), indicating reduced contrast with fewer projections. Non-square fields maintained high SSIM (0.99 for 10° vs. 5°) and negligible MSE, with CNR slightly decreasing from 12.7 (5°) to 11.1 (20°).
Conclusion: The 2D scintillation dosimeter successfully reconstructed square and irregular fields, with SIRT + TV offering the best performance. While 10° intervals balanced quality and efficiency, 5° intervals provided the highest precision. Minor deterioration at 20° intervals suggests that nine projections suffice for non-rotative, high-quality reconstructions, enabling efficient QA protocols and advanced beam attenuation analysis in radiotherapy.