S149
Brachytherapy - Physics
ESTRO 2026
open with AI-based treatment planning in prostate and cervix brachytherapy." Brachytherapy 23.2 (2024): 188-198.[2] Pötter, R., et al. "The EMBRACE II study: The outcome and prospect of two decades of evolution within the GEC-ESTRO GYN working group and the EMBRACE studies." Clin. and trans. radiation onc. 9 (2018): 48-60.[3] Ecker, S., et al. "EviGUIDE-a tool for evidence-based decision making in image-guided adaptive brachytherapy for cervical cancer." Radiotherapy and Onc. 186 (2023): 109748.[4] Pötter, R., et al. "MRI-guided adaptive brachytherapy in locally advanced cervical cancer (EMBRACE-I): A multicentre prospective cohort study." The Lancet Onc. 22.4 (2021): 538-547. Digital Poster 4950 New Verification Protocols for Treatment Planning Systems (TPS) in Brachytherapy ABEL RODRIGUEZ ARANDA 1,2 , ADRIAN ANDRADES 3 1 Medical Physics, Las Palmas University Hospital, Las Palmas, Spain. 2 Medical Physics, Lanzarote University Hospital, Arrecife, Spain. 3 Radiotherapy, Las Palmas University Hospital, Las Palmas, Spain Purpose/Objective: This study presents three experimental protocols for verifying the accuracy of treatment planning systems (TPS) in brachytherapy. The main goal is to evaluate and compare these methods to determine which provides the most reliable and practical verification approach for clinical implementation. Material/Methods: Each protocol corresponds to a specific experimental setup. Plastic (100–300 HU) and PMMA blocks of 2 cm and 5 cm thickness were used—one with an insert to accommodate a PinPoint ionization chamber—along with a PTW Unidos electrometer, Freiburg applicators, transfer tubes, plastic needles, and radiochromic films.For Method 1, the setup included Freiburg applicators (Figure 1). In Method 2, the same configuration was used but without Freiburg applicators. Method 3 replaced the Freiburg applicator with a 2 cm-thick plastic block (Figure 2).For each setup, a CT scan was acquired and two-needle treatment plans were generated in Oncentra Brachy. TPS-calculated doses at selected points and volumes were compared with experimental measurements from both the ionization chamber and film dosimetry.Dose values in nC were converted to Gy following the TG-43 formalism. Films were scanned using an Epson XL12000 scanner, and pixel-to-dose calibration was performed with ScanFilm and VeriSoft (MEPHYSTO-PTW) software.
Results: Method 1: The chamber measured 5.78 Gy, while the TPS calculated 5.59 Gy at the chamber point (3.29% relative error) and 5.31 Gy within the sensitive volume (8.13%). The film measured 3.29 Gy versus 2.83 Gy in the TPS (13.98%).Method 2: The chamber recorded 6.25 Gy compared to 5.97 Gy (5.26%) and 5.79 Gy (7.80%) in the TPS. The film showed 3.37 Gy vs 2.94 Gy (12.76%).Method 3: The chamber measured 2.37 Gy vs 2.42 Gy (2.11%) and 2.17 Gy (8.44%) in the TPS. The film yielded 6.25 Gy vs 5.78 Gy (7.52%).Overall, Method 3 consistently exhibited the smallest discrepancies in both point and film dosimetry, indicating superior agreement between measured and calculated doses. These results confirm that this protocol offers improved precision, lower variability, and easier implementation, making it the most robust option for clinical TPS verification. Conclusion: In conclusion, among the three evaluated setups, Method 3 (based on the PinPoint ionization chamber configuration) proved to be the most accurate, reproducible, and clinically feasible. It can be recommended as a new standard protocol for TPS
verification in brachytherapy. Keywords: TPS, Verification, QA
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