External Beam Therapy

External beam radiation therapy involves a series of daily treatments that accurately deliver radiation to the area needing treatment. The radiation beam usually comes from a machine called a linear accelerator. Before beginning treatment, you will be scheduled for a session to map out the area to be treated. This will frequently involve having a CT scan. Landmarks placed on your skin (often tiny tattoos) allow the radiation therapists delivering your treatments to position you in the same position each day.

To minimize side effects, the treatments are usually spread out over several weeks, five days a week (Monday through Friday). This allows your doctors to get enough radiation into your body to kill the tumor cells, while giving healthy cells time to recover each day.

Technical terms that may be mentioned for colorectal and anal cancer treatments include three dimensional conformal radiation therapy (3-D CRT), intensity modulated radiation therapy (IMRT) and image guided radiation therapy (IGRT). Your radiation oncologist can provide more information about these different techniques.