ESTRO 2022 - Abstract Book

S506

Abstract book

ESTRO 2022

Conclusion Ultra-hypofractionated adjuvant/salvage SBRT seems to be feasible and safe after radical prostatectomy. Longer follow-up is necessary to confirm observed results.

PD-0577 Patient-reported acute urinary toxicity after daily adaptive MR-guided SBRT for prostate cancer

T. Willigenburg 1 , F.R. Teunissen 1 , J. van der Velden 1 , J. de Boer 1 , J. van der Voort van Zyp 1

1 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands

Purpose or Objective While severe toxicity rates after stereotactic body radiation therapy (SBRT) for the treatment of prostate cancer (PCa) are low, many patients still experience moderate toxicity – especially genito-urinary – that can impact quality of life (QoL). The introduction of magnetic resonance (MR)-guided linear accelerators (MR-Linac) has enabled daily, high-quality imaging of soft-tissue in addition to daily re-planning. This potentially increases treatment precision compared to conventional linacs. However, clinical data on outcomes after 1.5T MR-Linac SBRT for prostate cancer is still scarce. We present short- term patient-reported outcomes regarding urinary toxicity in a prospective cohort of PCa patients treated with MR-guided SBRT. Materials and Methods PCa patients treated with 5x7.25 Gy on a 1.5T MR-Linac between March 2020 and May 2021, who participated in the prospective Utrecht Prostate Cohort (UPC) study (NCT04228211), were included (n=161). Patients with missing International Prostate Symptom Score (IPSS) data at baseline and/or no follow-up within three months post-treatment were excluded (n=29). Patients were treated over the course of 2.5 weeks using an ‘Adapt-to-Shape’ workflow with daily online re- contouring and re-planning. IPSS questionnaires were filled out at baseline (BL) and 1 month (1M) and 3 months (3M) after treatment. Patients with a clinically significant increase in IPSS ( ≥ 5 points from BL) within three months post-treatment were identified. Descriptive statistics were reported for baseline characteristics and differences between patients with and without a clinically significant increase in IPSS were assessed using appropriate statistical tests. IPSS at 1M and 3M was compared to BL using related-samples Wilcoxon signed rank test. A p-value <0.05 was considered statistically significant. Results Median (interquartile range) IPSS was 6 (4-10), 10 (7-16), and 7.5 (5-12) at BL, 1M, and 3M, respectively (Figure 1). Median IPSS was significantly higher at 1M and 3M compared to BL, and significantly lower at 3M compared to 1M. Out of 132 patients, 57 (43.2%) reported a clinically relevant increase in IPSS of ≥ 5 points. Besides a lower median baseline IPSS, no significant differences in characteristics between those with and without a clinically relevant increase in IPSS ( ≥ 5 points vs <5 points) were observed (Table 1).