ESTRO 2023 - Abstract Book

S148

Saturday 13 May

ESTRO 2023

treatment localization and intrafraction monitoring for intracranial treatment sites, provided by high definition submillimetric SRS precision mode, also for non-coplanar fields. To take advantage of SGRT, a well-structured clinical implementation is recommended and therefore, a comprehensive and site-specific workflow should be clearly defined. Several approaches will be covered during this lecture, for a global understanding of this straightforward and trendy available technology. In conclusion, based on the international survey, despite some weaknesses the majority of participants believe that SGRT will become standard of care.

SP-0213 The role of patient preparation strategies with real-time adaptive radiotherapy M.Chamberlain Switzerland

Abstract not available

Mini-Oral: Prostate

MO-0214 Impact of UK National Prostate Cancer Audit: changing practice in a large UK centre V. Manik 1 , G. Doss 1 , S. Wong 1 , T. Greener 1 , S. Mannion 1 , M. Adams 1 , S. Naz 1 , J. Barber 1 , K. Innes 1 , T. Guerrero-Urbano 1 , S. Morris 1 , S. Hughes 1 , V. Mullassery 1 , V. Harris 1 , G. Azad 1 , I. White 1 , K. Morrison 1 , A. Aggarwal 1 , G. Ntentas 1 , S. Vivekanandan 1 1 Guys & St Thomas' NHS Foundation Trust, Clinical Oncology, London, United Kingdom Purpose or Objective UK National Prostate Cancer Audit (NPCA) reported higher late ≥ Grade 2 ( ≥ G2) rectal toxicity rates in prostate cancer patients treated with external beam radiotherapy (EBRT) in 2016 in our centre (16% vs 10% UK average). NPCA defines ≥ G2 toxicity as the need for large bowel procedure & a diagnosis indicating radiation toxicity within 2 years of EBRT. This triggered an internal review of all patients treated in 2016 to validate the NPCA findings, identify causes of higher toxicity All patients with prostate cancer treated with radical EBRT in 2016 at our institute were included in this retrospective study. Patient, tumour & radiotherapy (RT) characteristics and ≥ G2 rectal toxicity were collected from electronic records. Sigmoidoscopy reports were reviewed to identify rectal toxicity to correlate with NPCA findings. Accuracy of daily on-board image matching for a sample with ≥ G2 rectal toxicity were reviewed. The impact of mean rectal dose & maximum anterior- posterior (AP) rectal diameter on ≥ G2 rectal toxicity was assessed. Chi square, Mann Whitney & t-tests and logistic regression were used to test statistical differences. p-value of <0.05 was considered statistically significant. Results 281 of 290 patients treated with EBRT were reviewed (no follow-up data for 9 patients). ≥ G2 rectal toxicity was confirmed in 16%, similar to NPCA. There were no differences in patient & tumour characteristics between those with & without ≥ G2 rectal toxicity. 93% of those with ≥ G2 toxicity were treated with helical image guided intensity modulated radiotherapy (IG-IMRT) & it was statistically significantly associated with ≥ G2 toxicity (p=0.048). Fractionation was not significantly associated with toxicity. CTV to PTV margins were similar in patients with or without ≥ G2 toxicity. All pre-defined mandatory & optimal rectal dosimetric constraints were met in 100% and 93.7% with ≥ G2 toxicity respectively. Rectal V60<0.01% was met in 57.6% with ≥ G2 toxicity but this constraint was introduced in 2020. Higher rectal mean dose (>45Gy in 37 fractions & >35Gy in 20 fractions) was significantly associated with higher ≥ G2 toxicity (p=0.04). 36% with ≥ G2 toxicity had a rectal diameter ≥ 4.5cm. Further on-board CT matching correction was necessary in 13% of 134 images reviewed in a sample of 3 patients with ≥ G2 toxicity. & implement changes. Materials and Methods