S1662
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
quality assurance of small-field OFs is recommended in clinical radiotherapy. References: 1 Palmans H, Andreo P, Huq MS, Seuntjens J, Christaki K. Dosimetry of Small Static Fields used in External Beam Radiotherapy: An IAEA–AAPM International Code of Practice for Reference and Relative Dose Determination. Technical Report Series No. 483. Vienna: International Atomic Energy Agency; 2017. Keywords: Small field dosimetry, output factors, TRS- 483
representing non-irradiated cells. Results:
Air surrounding the wells with cells led to increased cell viability (over 100% for all setups), likely due to dose inhomogeneity or underdosing caused by reduced backscatter and uneven dose distribution near the plate edges. This effect was diminished when the wells surrounding the cells were filled with water, resulting in cell viability dropping below 84%, as water improved dose uniformity. The effect was consistent across both radiation doses. Cell placement further influenced outcomes: edge wells experienced a smaller reduction in viability from irradiation (84% at 2 Gy and 77% at 8 Gy) compared to central wells (63% at 2 Gy and 38% at 8 Gy), highlighting the impact of geometry and local environment on dose delivery and biological response. Conclusion: We showed that the setup used to analyse the dose- effect can lead to high variations. Water-filled wells provided greater dose uniformity and lower viability overall, while the central well placement produced a clearer, more pronounced dose-response, making it the preferred configuration for in vitro irradiation experiments. This approach offers a valuable resource for laboratories with limited equipment, enabling them to implement reliable cell irradiation protocols using only standard clinical devices. Keywords: cellular-irradiation, dose-uniformity Verification of dose measurements using customized phantoms for various applicator shapes NOZOMI NAKAJIMA, SATOSHI KITOH, KEIKO NEMOTO MUROFUSHI Radiation oncology, Tokyo Metropolitan Komagome Hospital, Tokyo, Japan Purpose/Objective: In brachytherapy, dose calculations rely primarily on the AAPM TG-43 [1] formalism which assumes uniform dose distributions regardless of the applicator material. However, when metallic applicators (e.g., stainless steel) are used, dose perturbations such as an increase in electron scattering and the photoelectric effect have been reported [2]. However, no suitable commercial phantoms are currently available for quality assurance (QA) dosimetry involving metallic applicators. Therefore, in this study, we aimed to develop phantoms that can Digital Poster 3180 accommodate various applicators. As the first stage, verification of dose measurement against the planning system using the developed phantoms are verified.
Digital Poster 3094
Optimizing cellular irradiation setup on a 6MV LINAC using a custom plexiglass phantom: a solution for resource-limited laboratories Cristina E Gheară 1,2 , Vlad A Gurghian 3 , Mădălina L Nistor 4 , Zoltán Bálint 1 1 Faculty of Physics, Department of Biomedical Physics, Babeș-Bolyai University, Cluj-Napoca, Romania. 2 Laboratory of Radiotherapy, The Oncology Institute "Prof. Dr. Ion Chiricuţă" Cluj-Napoca, Cluj-Napoca, Romania. 3 Laboratory of Radiotherapy, Medex Oncology Hospital, Târgu Mureș, Romania. 4 Personalized Medicine and Rare Diseases Department, MEDFUTURE - Institute for Biomedical Research “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania Purpose/Objective: Limited access to cell irradiators in the radiobiology laboratory led us to develop a cellular irradiation procedure using a 6MV linear accelerator. Integrating radiobiological experimentation into a radiation therapy department offers valuable opportunities to better understand radiation effects. To ensure precise and reproducible irradiation of cell cultures using a 6MV LINAC, we developed and tested a custom-built plexiglass phantom designed to optimize the cellular irradiation setup, thereby facilitating controlled and repeatable exposure conditions for in vitro experiments. Material/Methods: Four different irradiation setups were evaluated using murine B16-F10 melanoma cells cultured in 96-well plates. Nine wells were filled with 8,000 cells each. All plates were irradiated with single doses of 2 Gy and 8 Gy. The four setups consisted of different cell arrangements: one with cells positioned along the plate margins and one with cells at the centre of the plate. For each of the two arrangements, the wells not containing cells were either filled with water or left empty. Cell viability was assessed using an MTT assay, and all results were normalized to a control plate
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