ESTRO 2025 - Abstract Book

S1934

Clinical - Urology

ESTRO 2025

1351

Digital Poster Shortening proton therapy treatment time of high-risk prostate cancer patients using laxatives and CBCT guidance Stine E Petersen 1 , Vicki T Taasti 1 , Anne J Christensen 2 , Anne Vestergaard 1 , Christine V Madsen 3 , Heidi S Rønde 1 , Jimmi Søndergaard 4 , Lasse Bassermann 1 , Liliana Stolarczyk 1 , Morten Høyer 1 , Lise Bentzen 3 , Ludvig P Muren 1 1 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 2 Department of Clinical Oncology, Zealand University Hospital, Køge, Denmark. 3 Department of Oncology, Vejle Hospital, University Hospital of Southern Denmark, Vejle, Denmark. 4 Department of Oncology, Aalborg University Hospital, Aalborg, Denmark Purpose/Objective: Treatment of prostate cancer with proton therapy may be challenging because of daily changes of gas and/or feces in the rectum and bowel as well as changes in bladder filling. These changes may cause excessive shifts of the clinical target volumes compared to the planning CT, and consequently repositioning of the patient may be needed before the treatment can be delivered. The use of image guided radiotherapy (IGRT) is important for providing a precise and accurate proton treatment for prostate cancer. In this study, we report treatment time and number of CBCTs before and after introducing a daily IGRT CBCT evaluation scheme and prescription of daily laxatives. Material/Methods: Thirty-five high-risk prostate cancer patients treated with proton therapy within the Danish national randomized PROstate PROTON Trial [1] were included in the study; twenty-three patients treated before, and twelve patients treated after prescription of oral laxatives and initiation of a new CBCT evaluation scheme, Fig. 1. All patients received 78 Gy (RBE) to the prostate and/or the seminal vesicles in 39 fractions with 56 Gy (RBE) to the elective pelvic lymph nodes delivered using a simultaneous integrated boost technique. Our daily IGRT strategy is to match the daily CBCT to the planning CT based on bony anatomy (6D) and then on fiducials markers (3D) in the prostate gland. After introducing the CBCT evaluation scheme it has been part of our daily IGRT strategy. In this study, treatment time, defined as from start of the first CBCT to the end of the last treatment field, and preparation time, defined as from start of the first CBCT to start of the first treatment field, were recorded for all fractions. The number of CBCTs acquired before start of each treatment fraction was also recorded.