Radiotherapy for Colorectal Cancer

Treatment of colorectal cancer (along with other cancers) has come a long way. When early treatment methods could only curb the cancerous growth with limited effectiveness, it is now possible for patients to be completely cured of cancer by using a combination of different methods. The advances in personalized medicine have also laid the foundation for specially tailored cancer treatment plans that take into account each patient’s genomic makeup to prescribe the most effective treatment and maximize it.

These advancements, however, do not mean that older, conventional treatment methods are now obsolete. Take radiotherapy (sometimes called radiation therapy), for instance. It is one of, if not the oldest cancer treatment used (albeit it is also known to cause cancer with overexposure). While these days it is no longer used as a primary treatment for most cancers, it is still occasionally used in conjunction with other therapies to treat colorectal cancer, including cancer that has metastasized to other organs.

Thanks to advances in colon cancer treatments, radiotherapy is not frequently used as primary treatment given that alternatives such as chemotherapy are available.

However, radiotherapy may sometimes be used as part of neoadjuvant therapy alongside chemotherapy ahead of the primary treatment, usually surgery. This is done when the tumor is too large to operate on, and the radiation and chemotherapy will have to shrink the tumor down to a manageable size. Radiation can also be used to treat symptomatic tumors to improve pain or reduce bleeding.

It can also be used during colorectal cancer surgery to destroy any cancer cells within immediate vicinity of the extracted tumor, in a process referred to as intraoperative radiation therapy (IORT). Especially in cases where the cancer has spread to a nearby organ or through the intestinal wall, physically removing the cancer is not completely foolproof, and radiotherapy may be used to destroy any remnant cancer cells as part of adjuvant therapy.

Compared to treating colon cancer, radiotherapy sees more regular use in treating rectal cancer because the anatomic differences between the rectum and colon make complete surgical resection difficult.

Similar to colon cancer, radiotherapy is used as neoadjuvant therapy together with chemo to help reduce the tumor size as it may obstruct the rectal passage and make surgery difficult. Administering it before surgery is preferred by physicians, as it lowers the chances of damage to the sphincter muscles in the rectum, and also allows for nearby lymph nodes to be treated too.

More recently, a growing number of patients with rectal cancer are being managed non-operatively after receiving radiation and chemotherapy. Some patients who have complete elimination of their cancer on imaging (magnetic resonance imaging — MRI) and endoscopy can be managed with close surveillance. Some of these patients may eventually need surgery, but some will have elimination of their cancer without an operation. Receiving radiation first followed by chemotherapy increases the possibility of non-operative management.

External-beam radiation therapy (EBRT)

External-beam radiation therapy (EBRT) is used for both colon and rectal cancer. The procedure is similar to getting an x-ray but with more intense radiation. As the name suggests, the radiation is focused into the area of the body where the tumor is from an external source.

Three-dimensional conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT) are newer EBRT techniques that are able to target metastatic cancer that has spread from the colorectal regions to the liver and lungs. These methods are also able to minimize radiation exposure to nearby healthy tissues. These newer EBRT techniques are typically used if the tumors present are few but symptomatic, and surgery is not an immediately available option.

Brachytherapy

Also known as internal radiation therapy, brachytherapy is characterized by placing a radioactive source inside the body next to or near the tumor. In the case of rectal cancer, the radiation source is put inside the rectum via the anus, which helps minimize the reach of radiation to other parts of the body.

The radiation source comes in small pellets, which are put through a tube and travels a short distance to the rectum. This procedure is typically for patients who are unable to have surgery, or have recurrent rectal cancer.

Endocavitary radiation therapy

This form of radiation therapy is also used for patients who are unable to receive surgery, or have recurring rectal cancer after previously receiving radiation therapy to the pelvic area. For this procedure, a small balloon-like device is inserted into the rectum. It delivers high-intensity radiation for a few minutes. The treatment can also be used for small or early-stage rectal cancers.

Like many other colorectal cancer treatments, radiotherapy is not without its side effects. In fact, radiation exposure in other forms is well known as a potential cause of cancer, such as prolonged or frequent x-rays or other forms of radiation.

With radiotherapy, the intensity of the radiation is much higher and also done at more frequent intervals over the course of the treatment. This can lead to side effects including the following:

• Skin irritation such as redness, blistering or peeling as a result of exposure to radiation beams
• Rectal irritation, including diarrhea, pain during bowel movements, bowel incontinence and blood in the stool
• Nausea
• (If given neoadjuvant radiotherapy) Poor post-surgery wound recovery
• Sexual dysfunction; erectile dysfunction for men, vaginal irritation in women
• Scarring and fibrosis

In most of these side effects, the effects are not permanent and should improve over time after treatment is completed and the symptoms are treated. However, if the side effects are prolonged and do not go away, consult your doctor immediately to have the side effects treated. They can help you manage them and recommend suitable treatments to make you feel more comfortable. Ignoring any side effects could be unfavorable to your overall well-being, so it is essential to continuously communicate your concerns.