Prostate cancer is the most common cancer in men in the UK. Radiotherapy is one of the main treatments. It works by using radiation to destroy cancer cells. There are two main ways this can be given:

• External beam radiotherapy – radiation delivered from a machine outside the body
• Brachytherapy – small radioactive sources placed inside the prostate while the patient is asleep under a general anaesthetic

Even after treatment, the cancer can sometimes return. When it does, it most often comes back inside the prostate itself, which is called a local recurrence.

Research suggests that giving a second course of radiotherapy (either external beam or brachytherapy) may be a better option than surgery for many people, because it tends to cause fewer side‑effects. However, these two types of radiotherapy have never been directly compared, and we still don’t fully understand the side‑effects people may experience after treatment.

Modern external beam radiotherapy can now be given in very precise, highly focused doses using daily imaging. This approach is called ultra‑hypofractionated radiotherapy or SABR (stereotactic ablative radiotherapy). SABR is widely used in many other cancers, but we do not yet know how effective it is for treating prostate cancer that has come back after previous radiotherapy. We also have limited information about possible side‑effects.

This study wants to:

• Check if patients are comfortable being randomly assigned (by computer) to one of the two treatments—brachytherapy or SABR
• Learn more about the long‑term side‑effects of each treatment
• Understand how each treatment affects quality of life over time

Patients who take part will be followed up regularly and asked to complete questionnaires about their health and wellbeing.

The information from this study will help us decide whether a larger, full‑scale study is possible. It will also help future patients by providing clearer, more reliable information about their treatment choices if their prostate cancer returns.