ESTRO 2025 - Abstract Book

S2749

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Keywords: breast apbi VMAT References: 1. Becker S, Sabouri P, Niu Y, Prado K, Chen S, Nichols E, et al. Commissioning and acceptance guide for the GammaPod. Phys Med Biol. 2019;64(20):205021. 2. Nichols EM, Guerrero M, McAvoy S, Biggins T, Yi B, Becker SJ. Workflow guide to delivering a safe breast treatment using a novel stereotactic radiation delivery system. J Radiosurg SBRT. 2021;7(3):249-52. 3. Yi B, Becker SJ. Simplified method for determining dose to a non-water phantom through the use of ND,w and IAEA TRS 483 for the GammaPod. Phys Med. 2021;88:138-41.

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Digital Poster Personalized radiotherapy for patients with impaired lung ventilation Maria Poncyljusz, Justyna Bochenek-Cibor, Andrzej Radkowski, Magdalena Kisiel, Ewa Kudlak Radiotherapy Department, St. Lucas Hospital in Tarnow, Tarnow, Poland

Purpose/Objective: Patients who have inactive areas in the lungs due to previous diseases require individual treatment during radiotherapy. Ventilation lung scintigraphy performed using SPECT-CT (single-photon emission computed tomography) allows for precise localization of even small subsegmental perfusion and ventilation disorders. The aim of this study was to determine active areas in the lungs using SPECT-CT and then take them into account when preparing a radiotherapy treatment plan.

Material/Methods: The patient diagnosed with squamous cell carcinoma of the left lung (T4N0M0) was qualified for

chemoradiotherapy. Radiotherapy included irradiation with a dose of 60Gy in 30 fractions of the PTV (planning target volume) using the DIBH technique. The patient underwent a SPECT-CT examination using technetium Tc99m, and then two areas of increased activity were contoured in the Velocity 4.0 Varian Medical System Inc. system: lungs-A and lungs-HA, the boundaries of which were defined at the level of 330Bq and 820Bq, respectively (units in the Velocity system). A fusion of the SPECT-CT and the planning CT examination was performed. The planning CT with lungs-A and lungs-HA structures was sent to the Monaco Elekta TPS treatment planning system. Maintaining the same plan evaluation criteria for PTV and organs at risk, two treatment plans were prepared: a standard plan (plan S) and a plan minimizing the dose deposited in designated lung structures (plan M). The mean dose values, V5Gy, V10Gy and V20Gy were compared for the lungs-A and lungs-HA structures. Results: In plan M compared to plan S the dose deposited in lung structures was reduced from 12.8Gy to 10.9Gy for lungs-A and from 7.6Gy to 5.8Gy for lungs-HA. A volume reduction was also achieved: V5Gy from 59.16% to 41.28% for lungs-A and from 31.68% to 21.58% for lungs-HA, V10Gy from 36.32% to 23.43% for lungs-A and from 22.19% to 10.49% for lungs-HA, V20Gy from 20.67% to 18.48% for lungs-A and from 10.53% to 8.11% for lungs-HA. Conclusion: In cases where the patient's medical history requires the use of non-standard procedures to protect healthy areas of the lung, delineation of these areas and minimizing the dose in their volume allows for reducing the side effects of radiotherapy. It is important to reduce both the V5Gy value associated with the induction of secondary lung cancers and the V20Gy value correlated with radiation pneumonitis. Expanding the set of imaging data used in the preparation of the treatment plan with SPECT-CT seems to be important, especially for patients with impaired pulmonary ventilation.

Keywords: SPECT-CT, image fusion, personalized treatment