Colon / Anal Cancers (Lower GI)

A wide variety of GI tumors are treated with radiation therapy, notably cancers of the stomach, pancreas, and rectum. At many of these tumor sites, radiation is used in conjunction with chemotherapy either prior to surgery (preoperative radiotherapy) or following surgery (postoperative radiotherapy). Preoperative chemoradiotherapy is also commonly used prior to surgery in patients with esophageal carcinoma.

While surgery is the mainstay of treatment for most GI tumors, it is intentionally avoided in anal cancer in favor of concurrent chemoradiotherapy. Such an approach avoids the need for a permanent colostomy, improving patient quality of life.

Treatment Techniques

3DCRT

3DCRT plan in a patient with rectosigmoid cancer

A variety of radiation therapy techniques are used in the treatment of patients with GI tumors. The most common approach is three-dimensional conformal radiation therapy (3DCRT). The 3DCRT technique uses multiple shaped beams which help reduce the dose to the surrounding normal tissues.

Depending on the tumor site treated, two, three or even four radiation beams are used. The tumor site also determines how the beams are configured. In pancreatic cancer patients, three beams are used, entering anteriorly and from the right and left sides (lateral fields). This technique helps reduce dose to the posteriorly located kidneys. In rectal cancer patients, while three beams are also used, two lateral beams and a posterior beam are selected. This configuration reduces the dose to the anteriorly located small bowel.

Intensity Modulated Radiation Therapy (IMRT)

IMRTpancreatic

IMRT plan in a patient with pancreatic cancer

In recent years, a sophisticated form of 3DCRT known as intensity-modulated radiation therapy (IMRT) has been increasingly used in GI tumor patients. Unlike conventional approaches, IMRT uses highly modulated beams designed using sophisticated computerized optimization planning. Such beams conform the radiation dose to the shape of the tumor in 3D, reducing the volume of normal surrounding tissues receiving high doses.

Multiple researchers have reported promising results using IMRT in GI tumor patients.

IMRT is particularly helpful for patients with anal cancer. In such patients, conventional approaches result in the irradiation of large volumes of normal tissues, exposing patients to a wide range of toxicities. IMRT helps minimize the dose to these structures reducing the risk of treatment toxicities.

 

Helpful UCSF Internet Site:

UCSF Gastrointestinal Oncology.............................................http://cancer.ucsf.edu/gi/