ESTRO 2025 - Abstract Book

S1986

Clinical - Urology

ESTRO 2025

Treatment was canceled 34 times: 5 times due bones positions in field directions, 22 times due bladder volume: 17 times - underfillment, 5 overfillment. And 9 times in reasons of cancel was overfilled rectum. 8 treatments were canceled due to prostate movement, although it was associated with overfillment of rectum and bladder. In almost all cases there were multiply reasons to cancel treatment. Conclusion: 1. It is feasible to treat prostate cancer patient using proton therapy without an endorectal balloon. 2. The pelvic preparation protocol should be strictly followed, as fractions withdrawals were associated with unacceptable preparation and treatment volume shifts were directly correlated with unacceptable preparation

Keywords: proton therapy, prostate, nodal irradiation

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Digital Poster First toxicity and dosymetry data for prostate cancer with lymph nodes treated with large fractions proton therapy Nikita Kataev 1 , Andrey Luybinskiy 2 , Nikolay Vorobyov 1,3 , Georgiy Andreev 2 , Marina Linnik 1 , Nataliia Martynova 1 , Natalia Berezina 4 , Kirill Suprun 5,6 1 Proton Therapy, MIBS, Saint Petersburg, Russian Federation. 2 Medical Physics, MIBS, Saint Petersburg, Russian Federation. 3 Oncology, SPbU, Saint Petersburg, Russian Federation. 4 Administrative, MIBS, Saint Petersburg, Russian Federation. 5 Surgery, MIBS, Saint Petersburg, Russian Federation. 6 Surgery, SPbU, Saint Petersburg, Russian Federation Purpose/Objective: Five-fraction radiation therapy appears to be gaining popularity in treatment of prostate cancer, but it has not been extensively tested in the context of pelvic nodal irradiation. The objective of this study of ultrahypofractionated proton therapy for high and very-high risk prostate cancer is report acute toxicity and dosimetry data. This is preliminary data analysis of acute toxicity and dosimetry from first 18 patients. Material/Methods: This study was focused on patients with high and very high risk prostate cancer. Radiation therapy was planned to deliver 25Gy to pelvic nodes and a simultaneous integrated boost (SIB) of up to 36.25Gy to the prostate, seminal vessels and PET-PSMA positive pelvic nodes in 5 fractions, weekly, over 5 days. Common Terminology Criteria for Adverse Events version 5.0 was used to assess worst acute toxicities. We also evaluated doses for organs-at-risk (OAR) in treatment plans of those patients.

Results: The following “worst” acute toxicities ccording to NCI CTCAE v.5.0 criteria were observed:

— Grade 2 genitourinary toxicity, 11.1%(2/18); — Grade 1 gastrointestinal toxicity, 55,5%(10/18); No grade 3 or higher toxicities were observed. Another point of analysis was the dosimetry assessment. We evaluated doses for organs-at-risk (OAR) in treatment plans of those patients according to dose-volume constraints. Those date is shown in table below: