This study is looking at whether it is safe to treat high‑risk localised prostate cancer with a short course of radiotherapy given in only 5 hospital visits.

The type of radiotherapy being tested is called stereotactic body radiotherapy (SBRT). SBRT is a very precise form of external radiotherapy that delivers higher doses to the cancer with great accuracy. For some cancers, SBRT has already been shown to be very effective.

In this study, we will offer SBRT to 536 men with high‑risk prostate cancer that has not spread beyond the prostate, but is more likely to grow quickly or spread in the future.

Participants will be randomly placed into one of two groups:

1. Radiotherapy to the prostate only
2. Radiotherapy to the prostate and the nearby lymph glands

We want to find out:

• Whether SBRT is safe, by closely monitoring any side‑effects
• Whether treating the lymph glands as well as the prostate helps reduce the chance of the cancer coming back

• All participants will receive 5 radiotherapy treatments over two weeks.
• Treatment will be given at NHS radiotherapy centres with specialist experience in SBRT and pelvic radiotherapy.
• These centres have been checked to make sure they can safely deliver this advanced treatment.
• Patients will be followed up for at least three and a half years so we can see which treatment works best and whether the cancer returns.

If SBRT is found to be safe and effective when used in this way, it could offer future patients:

• A potentially curative treatment
• A much shorter treatment schedule
• Fewer hospital visits
• More information to help guide treatment decisions