Radiotherapy treats cancer by using high-energy rays that destroy the cancer cells. It can either be given as external radiotherapy from outside the body using x-rays, or from within the body as internal radiotherapy (brachytherapy).
Usually, there will be no medical reason to stop having sex during external radiotherapy. But, if you have unpleasant side effects from the treatment, you may lose interest in sex until you recover. If you have radiotherapy to the area between the hips (pelvis), or if you have internal radiotherapy, your doctor or specialist nurse can tell you if this will affect your sex life during treatment.