S1627
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
standardization are warranted to establish CI as a routine verification tool in radiation oncology. References: Glaser AK et al., Nat Commun, 2020Cherenkov PA, Phys Rev, 1937Jarvis LA et al., Med Phys, 2014Zhang R et al., Int J Radiat Oncol Biol Phys, 2022Axelsson J et al., Phys Med Biol, 2023Moran JM et al., Pract Radiat Oncol, 2017Cerviño LI et al., Phys Med Biol, 2011Thomas EM et al., J Appl Clin Med Phys, 2021Diffenderfer ES et al., Med Phys, 2020Bruza P et al., Phys Med Biol, 2021. Keywords: Cherenkov Imaging, Dose Detection, SGRT Mini-Oral 547 Development of a clinically viable radiochromic formulation for real-time dosimetry Rachel L. Shum 1 , Rohith Kaiyum 2 , Alexandra Rink 3,4 1 Medical Physics, Princess Margaret Cancer Centre, Toronto, Canada. 2 Physics and Astronomy, York University, Toronto, Canada. 3 Medical Biophysics, University of Toronto, Toronto, Canada. 4 Radiation Oncology, University of Toronto, Toronto, Canada Purpose/Objective: Radiochromic commercial film dosimeters have been used since the early 1990s. Although Gafchromic™ EBT radiochromic films exhibit high sensitivity and effective dose response, their response is inherently nonlinear.1,2 Their predecessor, MD-55 films, exhibit a linear dose response but lower sensitivity, with an absorbance maximum (λmax) near 670 nm that can interfere with infrared dyes used for material thickness self-calibration.3 This work investigates zinc pentacosadiynoate-based (ZnPCDA) radiochromic materials as potential alternatives for clinical real-time dosimetry, focusing on formulation and dose- response characteristics under photon beam irradiation. Material/Methods: ZnPCDA radiochromic films were formulated and coated in-house following a modified literature procedure.4 Formulations with varying stoichiometric zinc feed ratios were prepared to evaluate their influence on dose response. Films were irradiated using a high-energy photon beam (Varian TrueBeam) at clinically standard doses and dose rates in a custom phantom setup equipped with integrated optical fibres for real-time transmission-mode spectroscopy measurements. Change in absorbance and optical density over a defined spectral range were quantified following established methodologies.5 Dose-response characteristics were analyzed to assess sensitivity and linearity. Results: ZnPCDA formulations exhibited a λmax of ~640 nm
(Figure 1) for all molar feed ratios, well separated from infrared dyes used for self-calibration (λmax ≈ 820 nm)3. Films prepared with substoichiometric zinc molar feed ratios demonstrated higher apparent sensitivity, indicated by a greater change in optical density with dose. The change in optical density normalized to film thickness (∆ODt), peaked with a zinc molar feed ratio of 0.3 whereas 0.1 and 0.5 equivalents showed lower sensitivity (Figure 2, left). For ZnPCDA films formulated with 0.3 equivalents of zinc, ∆ODt increased linearly with dose, with a coefficient of determination (R2) = 0.9993 (Figure 2, right).
Figure 1. UV-Vis absorption spectra of exposed ZnPCDA films formulated with varying zinc molar feed ratios. λmax is observed at ~640 nm.
Figure 2. Left: ∆ODt as a function of zinc molar feed ratio following photon beam irradiation at 1500 cGy. Right: ∆ODt as a function of delivered dose for films formulated with a 0.3 zinc molar feed ratio. Inset: images of films following irradiation at increasing doses. Conclusion: ZnPCDA radiochromic formulation demonstrate a strong potential for real-time clinical dosimetry owing to their facile one-pot formulation, blue-shifted λmax that enables infrared dye incorporation, and linear dose-response characteristics. Compared to commercial MD-55 films, ZnPCDA films exhibit higher sensitivity, and unlike EBT films, they provide a more linear dose response, making them well suited for real-time dosimetry applications. References: 1. Rink, A.; Vitkin, I. A.; Jaffray, D. A. Med Phys2005, 32, 2510–2516. DOI: 10.1118/1.19514472.Chiu ‑ Tsao, S.; Ho, Y.; Shankar, R.; Wang, L.; Harrison, L. B. Med Phys2005, 32, 3350–3354. DOI: 10.1118/1.20654673. Kaiyum, R.; Schruder, C. W.; Mermut, O.; Rink, A. Med
Made with FlippingBook - Share PDF online