Radiation Therapy for Rectal Cancer

Overview

Radiation therapy, or radiotherapy, is a common way to treat rectal cancer. Doctors who specialize in treating cancers with radiation are known as radiation oncologists. Radiation therapy involves the use of high-energy x-rays to kill cancer cells. For many rectal cancers, radiation therapy is used after surgery to destroy any cancer cells that may remain in the area of the operation. In advanced stages of rectal cancer, radiation therapy is often given before surgery to shrink the cancer, or instead of surgery when an operation cannot be performed. Radiation therapy is also commonly given in combination with anti-cancer drugs (chemotherapy). Chemotherapy has the ability to kill cancer cells directly and make radiation therapy more effective in killing cancer cells.

Radiation therapy for rectal cancer is typically given by a machine that aims x-rays at the body (external beam radiation). External beam radiation therapy (EBRT) for rectal cancer is given on an outpatient basis, 5 days a week, for approximately 5 to 6 weeks. EBRT begins with a planning session, or simulation, where marks are placed on the body and measurements are taken in order to line up the radiation beam in the correct position for each treatment. A program of daily treatments is then begun where the patient lies on a couch and is treated with radiation from multiple directions to the pelvis. The radiation oncologist may perform a second planning session or simulation near the end of treatment to focus the radiation to the area where cancer cells are most likely to remain. The last 3-5 days of treatment may be directed at this area.

Although patients do not feel anything while receiving a radiation treatment, the effects of radiation gradually build up over time. Many patients become somewhat fatigued as treatment continues. Loose stools or diarrhea are also common. Urination may become more frequent or uncomfortable. Some patients may experience loss of pubic hair or irritation of the skin. When radiation therapy is given with 5-fluorouracil chemotherapy, diarrhea can be worse. In a small percentage of patients, an obstruction or blockage in the small bowel can occur, which may require hospitalization or even abdominal surgery to relieve. Radiation therapy can also cause chronic changes in bowel function, resulting in loose stools and inflammation of the prostate when severe.

Some radiation oncology centers have special treatment equipment for certain circumstances. For small early cancers, a focused radiation beam can be aimed directly at the cancer in the rectum. Intra-operative radiation therapy (IORT) refers to treatment in a specially equipped operating room where a single dose of radiation is given during the surgery. The radiation doctor is able to see the area being treated directly and move sensitive normal structures, such as the small bowel, away from the radiation beam. IORT is usually administered when surgery is being performed for locally extensive cancer or stage II-IV cancer that has recurred in the pelvis.

Strategies to Improve Treatment

The progress that has been made in the treatment of rectal cancer has resulted from improved development of radiation treatments and surgical techniques and participation in clinical trials. Future progress in the treatment of rectal cancer will result from continued participation in appropriate clinical trials. Currently, there are several areas of active exploration aimed at improving radiation treatment of rectal cancer.

Newer Radiation Techniques: External Bean Radiation Therapy (EBRT) can be delivered more precisely to cancer-containing areas by using a special CT scan and targeting computer. This capability is known as three-dimensional conformal radiation therapy, or 3D-CRT. The use of 3D-CRT appears to reduce the chance of injury to nearby normal body structures, such as the bladder or rectum. Since 3D-CRT can better target the area of cancer, radiation oncologists are evaluating whether higher doses of radiation can be given safely with greater cancer cures.

Newer Radiation Machines: Most EBRT uses high energy x-rays to kill cancer cells. Some radiation oncology centers use different types of radiation, which require special machines to generate. These different types of radiation, such as protons or neutrons, appear to kill more cancer cells with the same dose. Combining protons or neutrons with conventional x-rays is one method of radiation therapy being evaluated in clinical trials.

New Radiation Therapy Modalities: Intraoperative radiation therapy (IORT) is given in specially-equipped operating rooms to deliver a single dose of radiation directly to the area of surgery. The radiation doctor is able to see the area being treated directly and move sensitive normal structures, such as the small bowel, away from the radiation beam.

Neoadjuvant Therapy: When rectal cancer cannot be completely removed with surgery, a patient’s chance of cure is greatly diminished. Presurgery radiation and/or chemotherapy is referred to as neoadjuvant therapy. Neoadjuvant therapy can shrink some rectal cancers and therefore allow complete surgical removal. Determining the optimal neoadjuvant chemotherapy and radiation therapy is an area of current research.

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