ESTRO 2025 - Abstract Book

S4056

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

tumours were more likely to be detected by XLTS, while central and diaphragmatic tumours were unlikely to be detected by XLTS (making them unsuitable for XLTS treatment). Success rate can significantly improve with a larger tumour diameter (>15.0 mm), volume (>2.0 cm 3 ), greater HU (>60.0 HU), and optimised simulation techniques. Conclusion: This study established the first comprehensive patient selection guideline for CyberKnife ® simulation to minimise patient treatment delays and potentially eradicate unnecessary need for invasive fiducial implantation. This will permit a broader range of lung cancer patients to be appropriately triaged towards the optimal treatment modality. References: 1. World Health Organisation (WHO). Lung Cancer. 2023. Available from: https://www.who.int/news-room/fact sheets/detail/lung-cancer 2. Ball D, Mai GT, Vinod S, Babington S, Ruben J, Kron T, et al. Stereotactic ablative radiotherapy versus standard radiotherapy in stage 1 non-small-cell lung cancer (TROG 09.02 CHISEL): a phase 3, open-label, randomised controlled trial. Lancet Oncol. 2019 Apr;20(4):494-503. DOI: 10.1016/S1470-2045(18)30896-9. 3. Kord M, Kluge A, Kufeld M, Kalinauskaite G, Leobel F, Stromberger C, et al. Risks and benefits of fiducial marker placement in tumor lesions for robotic radiosurgery: technical outcomes of 357 implantations. Cancers. 2021;13:4838. https://doi.org/10.3390/cancers13194838 Poster Discussion Impact of Hydrogel Spacer on Quality of Life and Dosimetry in Hypofractionated External Beam Radiotherapy for Localized Prostate Cancer Aravind Prakash 1,2 , Samuel Worster 1 , Meheli Chatterjee 1 , Farasat Kazmi 1 , Gaurav Kapur 1 , Robert Wade 1 , David Maskell 1 , Helen Swannie 1 , Jenny Nobes 1 1 Oncology, Norfolk and Norwich University Hospitals NHS foundation Trust, Norwich, United Kingdom. 2 Oncology, Cambridge University Hospitals NHS foundation Trust, Cambridge, United Kingdom Purpose/Objective: Despite the success of radical external beam radiotherapy (RT) in treating localized prostate cancer, late bowel toxicities remain a concern due to the proximity of the rectum to the high-dose planning target volume (PTV). Hydrogel spacer technology can increase the separation between the rectum and prostate resulting in lower RT related toxicities to the rectum in patients with prostate cancer treated with curative intent RT. In this single institution study, we aim to evaluate the real world outcome of effects of hydrogel spacer in RT on dosimetry and late rectal toxicities compared to those patients who had standard RT alone for localized prostate cancer. Material/Methods: Between 2020 and 2022, retrospective data were collected for consecutively treated patients with localized prostate cancer who received standard RT 60Gy in 20 fractions alone (Control) and those who received standard RT with hydrogel spacer insertion (Spacer group). Quantitative analysis included rectal dose distribution, prostate volumetric differences, and mean separation distance (prostate - rectum). The EPIC-26 questionnaire was conducted 2 years post-treatment to assess late rectal toxicities. Group comparisons were performed using T- test. Results: A total of 59 patients with localised prostate cancer (Spacer group: 29, Control group: 30) received RT. The median time from completion of treatment was 30.1 months (IQR: 27.4 – 37.7). Overall, 18 (62%) patients in the spacer Keywords: CyberKnife, Xsight, soft tissue tracking 871