Quantitative Cherenkov-excited fluorescence emission dosimetry for HDR Co-60 brachytherapy: Calibration and planar validation against TPS
Journal of Applied Clinical Medical Physics, cilt.27, sa.9, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 27 Sayı: 9
- Basım Tarihi: 2026
- Doi Numarası: 10.1002/acm2.70785
- Dergi Adı: Journal of Applied Clinical Medical Physics
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Applied Science & Technology Source, EMBASE, MEDLINE, Directory of Open Access Journals, Health Research Premium Collection (ProQuest)
- Anahtar Kelimeler: 60Co brachytherapy, Cherenkov emission, fluorescence, optical dosimetry, quality assurance
- Hacettepe Üniversitesi Adresli: Evet
Özet
Background: Accurate dose verification in High-Dose-Rate (HDR) brachytherapy presents a significant challenge due to steep dose gradients and the absence of beam collimation. Conventional quality assurance (QA) methods typically rely on point detectors or film-based techniques, which lack the capability to provide real-time, full-field visualization of dose distributions in a water-equivalent medium. While Cherenkov emission (CE) imaging has been investigated for Iridium-192 (192Ir) systems, the low mean photon energy of 192Ir (∼380 keV) constrains the optical yield and limits the signal-to-noise ratio. Because Cobalt-60 (60Co) emits higher primary photon energies, it generates distinct Cherenkov intensities and spatial characteristics, requiring dedicated evaluation. Purpose: This study aims to characterize the relationship between Cherenkov emission intensity and absorbed dose generated by an HDR 60Co source. Furthermore, it seeks to generate high-resolution two-dimensional dose maps using Cherenkov-excited fluorescence imaging and validate their dosimetric accuracy against Treatment Planning System (TPS) calculations to evaluate the system for clinical QA implementation. Methods: A custom 3D-printed polylactic acid (PLA) phantom was fabricated with an internal cavity filled with an aqueous quinine hemisulfate solution (1 g/L). This solution was used to convert ultraviolet Cherenkov photons into isotropic visible fluorescence, thereby enhancing optical signal detection. Optical emissions were captured using a standard monochrome CMOS camera positioned at a 24 cm working distance. To eliminate radiation-induced artifacts on the sensor without relying on complex time-gated hardware, an image processing pipeline comprising dark frame subtraction, median filtering, and morphological operations was applied. A calibration function was established by delivering doses between 10 and 1500 cGy using a 60Co HDR afterloader. Dosimetric accuracy was then evaluated across ten independent verification plans using two-dimensional gamma index analysis with 3% dose difference and 3 mm distance-to-agreement (3%/3 mm) criteria. Results: The dosimetric calibration demonstrated a highly predictable and linear dose-response relationship, yielding a coefficient of determination (R2) of 0.9999 and a root mean square error (RMSE) of 3.46 cGy. For the clinical verification plans, the CE-derived 2D dose maps exhibited strong spatial agreement with the TPS calculations. Gamma passing rates across the ten plans ranged from 91.6% to 97.3%, resulting in a mean passing rate of 94.2% ± 1.9% and an average mean gamma value of 0.57 ± 0.05. One-dimensional line profiles further confirmed the high spatial fidelity of the system in accurately tracking steep dose fall-offs. Conclusion: The integration of Cherenkov-excited fluorescence imaging with a standard CMOS sensor provides a highly linear, practical, and cost-effective planar dose verification tool for continuous-emission 60Co HDR brachytherapy. The proposed methodology mitigates the signal limitations inherent to lower-energy isotopes and achieves strong spatial agreement with TPS calculations, supporting its reliability as an independent QA modality in a controlled phantom environment.