Colorectal cancer is a common cancer. It typically occurs in people older than 50, with the risk increasing with age. About 5% to 20% of people with colorectal cancer have locally advanced disease, in which the cancer has invaded nearby tissues. After primary resection to remove the tumour, it returns in the same place in about 5% to 20% of people.
There are various treatments for colorectal cancer, including resection, chemotherapy and radiotherapy. Treatment choice depends on the type of cancer, location and staging. The radicality of resection is the most important prognostic factor for survival. Resection is referred to as: R0, when there are clear margins around the tumour; R1, when there are microscopically involved margins; and R2, when there are macroscopically involved margins or gross residual disease.
The procedure is done during surgery for locally advanced or locally recurrent colorectal cancer. Once the tumour is resected, the patient is positioned to receive a megavoltage electron dose from a linear accelerator. This can happen in the operating theatre if it's equipped with a stationary linear accelerator. Otherwise, the person is transferred to a dedicated room, or a mobile linear accelerator is brought into the theatre. Radiation-sensitive organs surrounding the tumour site can be displaced or shielded from the intraoperative electron beam radiotherapy (IOERT) field. A single large fraction of radiation (typically 10 Gy to 20 Gy) is then delivered by an applicator directly to the tumour bed. The aim is to improve local control and increase survival rates.
There are several techniques for delivering intraoperative radiotherapy, including IOERT, high dose rate brachytherapy, and orthovoltage. This guidance relates to IOERT only, not high dose rate brachytherapy or orthovoltage techniques.