KEY POINTS
- The UK National Prostate Cancer Audit reported 16% severe late GI toxicity among prostate cancer patients treated with EBRT at this large academic centre in 2016, compared with a 10% national average.
- Investigators reconstructed the entire pathway for 290 treated patients; robust follow-up was available for 281/290 (96.8%). Detailed clinical and endoscopic review confirmed severe late GI toxicity in 45 patients (16%), including 43 with directly visualized radiation proctitis.
- Patient age, PSA, Gleason score, stage, fractionation and CTV-to-PTV margins were not significantly associated with severe toxicity. Instead, a higher rectal mean dose—>45 Gy with 74 Gy/37 fractions or >35 Gy with 60 Gy/20 fractions—was significantly associated with toxicity (p=0.043).
- 36% of affected patients had a maximum rectal diameter ≥4.5 cm on planning CT, highlighting reproducibility and rectal-filling issues that standard dose constraints alone did not capture.
- Independent review of daily IGRT for three patients with the most severe toxicity found that 17/134 images (13%) would retrospectively have warranted additional 3–7-mm setup corrections.
- The centre consequently introduced tighter rectal constraints, selective daily enemas for large rectal diameter, reduced CTV-to-PTV margins, target/OAR peer review, improved image-matching pathways and a limited rectal-spacer program.
- In the subsequent national re-audit of 369 patients treated in 2022, severe late GI toxicity had fallen to 7.5% from 16%. Because multiple interventions changed simultaneously in a historical pre/post comparison, the contribution of any individual intervention cannot be isolated.
CLINICAL TAKEAWAY
Meeting conventional plan constraints does not guarantee optimal toxicity outcomes. This study shows the value of combining national outcome benchmarking with review of dosimetry, anatomy, setup, contouring and IGRT as one treatment pathway rather than treating QA as a purely technical pre-treatment exercise.