ESTRO 2024 - Abstract Book

S2481

Clinical - Urology

ESTRO 2024

time at the recurrence. These very preliminary data suggest that PSMA-PET-derived quantitative indexes could be useful for staging, in particular the volumetric parameters.

Keywords: PSMA-PET PCa oligometastatic

1993

Digital Poster

Correlating acute bowel toxicity with RT planning objectives for high-risk prostate cancer patients

Jakob B. Overgaard, Lars U. Fokdal, Christine V. Madsen, Ahmed H. Zedan, Martin Berg

Vejle Hospital, University Hospital of Southern Denmark, Department of Oncology, Vejle, Denmark

Purpose/Objective:

Treatment of high-risk prostate cancer patients with standard radiotherapy (RT) include 56 Gy in 39 fractions to the elective pelvic lymph nodes and seminal vesicles; and a simultaneous integrated boots to the prostate alone or prostate and seminal vesicles to 78 Gy in 39 fractions. Pelvic RT will inevitably result in a significant radiation dose to the bowel and therefore a risk of acute and late bowel related adverse effects. Dose planning involves RT planning objectives that are not necessarily linked directly to a clinical relevant side effect. By combining the planning dose with the reported bowel related problems following RT, it is possible to estimate a risk for relevant side effects to be used in future radiotherapy. The aim of this study is to investigate a possible relationship between bowel V50 Gy and V35 Gy, and acute bowel toxicity. This knowledge can be used to better inform patients upfront on their RT course. Between October 2017 and June 2022, patients diagnosed with high risk prostate cancer receiving curative intended RT were enrolled in a prospective registration protocol regarding adverse effects following RT. The protocol has been based on international questionnaires on adverse effects and includes CTCAE v4.0, the Expanded Prostate Cancer Index Composite (EPIC), EORTC QLQ-C30, and a segment of EORTC QLQ-PR25. All dose plans were optimized to reduce and keep V50 Gy < 200 ccm and V35 Gy < 40% for the bowel cavity. As a result of overlap between the bowel cavity and planning target volume (PTV) for the elective lymph nodes, the latter always being prioritized, the constraints are often exceeded. The present work focuses on bowel morbidity assessed during the follow- up’s (FU) at 4w, 3m, 6m, 9m, and 12m after end of RT treatment (EoT). Based on the bowel related questions from the EPIC questionnaire (items 42-55), an average bowel score was calculated for all patients at baseline (BL) prior to RT and at every FU. The score ranges from 0 to 100 where 100 represents no bowel related problems at the time of FU. Material/Methods: