1004 - Driving Improvement in Prostate Cancer Radiotherapy Outcomes through a National Quality Assurance Program: Results from a Large UK Academic Center

Purpose/Objective(s): UK National Prostate Cancer Audit (NPCA) is the largest international quality assurance program in prostate cancer (PC) which reports annually hospital level PC radical treatment outcomes for all public sector UK hospitals. In 2019, our 10 Linac centre had an NPCA reported grade 2 or higher rectal toxicity rate (=G2RT) at 2 years following external beam radiotherapy (EBRT) of 16%. This was higher than the UK average of 10%. We report a systematic multi-disciplinary review of EBRT pathway triggered by this to identify causes of higher toxicity, the subsequent practice changes implemented with an aim to reduce =G2RT rate and the results of the NPCA re-audit.

Materials/Methods: In 2019, we reviewed all PC patients treated with radical EBRT in 2016 and their follow up data for 2 years, up to 2018. We conducted a multi-disciplinary review of the EBRT pathway as part of a root cause analysis involving clinicians, physicists, radiographers and data managers. Patient, tumour, radiotherapy characteristics and =G2RT based on RTOG scale were collected from electronic notes and sigmoidoscope reports. EBRT plans were reviewed to assess rectal dosimetry. Impact of mean rectal dose and maximum anterior-posterior (AP) rectal diameter on =G2RT and accuracy of daily on-board image matching for a sample with =G2RT was assessed. Protocols from UK centres with lower toxicity were reviewed. Chi square, Mann Whitney & t-tests and logistic regression were used to test statistical differences. p-value of <0.05 was considered statistically significant. Based on the findings, a consensus based new treatment protocol was implemented in 2021.

Results: 281 of 290 patients treated with EBRT in 2016 had follow up data. =G2RT was confirmed in 16%. There were no significant differences in patient and tumour characteristics or fractionation between those with and without =G2RT. CTV to PTV margins were similar in patients with or without =G2RT. All pre-defined mandatory and optimal rectal dosimetric constraints were met in 100% and 93.7% with =G2RT respectively. Higher rectal mean dose (>45Gy in 37fr & >35Gy in 20fr) was significantly associated with =G2RT (p 0.04). 36% with =G2RT had a rectal diameter =4.5cm. Further on-board CT matching correction was recommended in 13% of 134 images reviewed in 3 patients with highest =G2RT. We implemented the following changes between 2020 and 2021: rectal constraints (mean dose, V60/V74 <0.01%), encouraged enema use, re-developed radiographer verification treatment decision pathway, reduced CTV to PTV margins following a contouring study.

Conclusion: In 2024, NPCA reported our =G2RT rate at 2 years in PC patients treated with radical EBRT in 2021 had decreased to 7.5%. This study highlights the value of national radiation toxicity audits in prompting robust internal multi-disciplinary reviews resulting in changes to improve patient outcomes.