Cancer of the sinuses (the air‑filled spaces around the nose) is rare, but it can be very serious. Because symptoms can be vague at first, the cancer is often quite advanced by the time it is diagnosed.

Radiotherapy is an important part of treatment. It can be used after surgery to destroy any remaining cancer cells, or it can be used on its own if surgery is not possible. Sometimes chemotherapy is added as well.

Giving radiotherapy in this area can be challenging because the sinuses sit close to very delicate structures such as the eyes and the brain. This means radiotherapy can sometimes cause long‑term side effects, including eye pain, loss of vision, problems with memory or thinking, epilepsy, sinus blockage or inflammation, reduced hormone levels, and difficulties with hearing or smell.

The standard type of radiotherapy currently used is called intensity‑modulated radiotherapy (IMRT). IMRT shapes the radiation more precisely, helping to improve cure rates and reduce side effects compared with older techniques.

Proton beam therapy (PBT) is a newer type of radiotherapy that may target the tumour even more accurately. This study will compare how well PBT works compared with standard IMRT. It will also look at the side effects of both treatments to see whether one causes less damage than the other.

People who join the study will be randomly allocated (like flipping a coin) to receive either standard IMRT at their local hospital or PBT at one of the specialist proton centres in Manchester or London. Treatment will take place over 6–7 weeks.

All other treatment decisions will be the same whether or not someone takes part in the study. After radiotherapy finishes, participants will attend routine follow‑up appointments for up to 5 years. These visits match normal care and allow the team to monitor any side effects.