Endorectal high dose rate (HDR) brachytherapy for rectal cancer is usually carried out with the patient under sedation. Before treatment the tumour size and stage are determined using imaging techniques. A 3‑dimensional CT‑based treatment planning system may be used to guide the positioning and dose of radiation. Radio‑opaque clips may be placed, using proctoscopy or sigmoidoscopy, to mark the margins of the tumour.
A rigid or flexible endorectal applicator is inserted into the rectum and used to deliver the radiation source to the tumour. The radioactive material is moved from the brachytherapy machine into the applicator and is left in place to deliver the correct dose of radiation to the tumour. A balloon may be placed over the applicator to displace the uninvolved rectal mucosa away from the radioactive material, to reduce toxicity. When the balloon is inflated, it immobilises the applicator and also helps to facilitate close contact with the tumour. When the treatment is over, the radioactive material is moved back into the machine and the applicator is taken out. Surgery to remove any remaining tumour is done a few weeks after completion of brachytherapy.