Radiation Therapy for Colorectal Cancer

Doctors at NYU Langone’s Perlmutter Cancer Center may prescribe radiation therapy, in which energy beams destroy cancer cells in a non-invasive manner. It is often combined with chemotherapy, which may make the radiation more effective. This approach is called chemoradiation.

Doctors may recommend radiation therapy or chemoradiation before surgery to help shrink tumors and prevent cancer from recurring after surgery. They may also prescribe chemoradiation after surgery to help rid the body of any remaining cancer cells.

Radiation therapy may also be used when surgery is not recommended because of the associated risks or side effects.

Dr. Alec Kimmelman Reviews Images

Dr. Alec Kimmelman reviews radiology images with staff.

Radiation therapy may also be recommended for the relief of some of the symptoms of colorectal cancer, such as bleeding, pain, or difficulty with bowel movements. If the colorectal cancer has spread to other parts of the body, such as the liver, radiation may be recommended to target these areas. Sometimes, radiation is used to alleviate symptoms when colorectal cancer has spread to the bones.

Treatment Planning

Our radiation oncologists develop a customized treatment plan that’s tailored to your needs. They use the latest technology to obtain images of the tumor and surrounding tissue and organs. Using computer-based treatment planning systems, our team of doctors and medical physicists determine how to best target the cancer while sparing healthy tissue, allowing them to maximize the therapeutic effect of radiation while reducing the risk of side effects.

Image-Guided Radiation Therapy

Our doctors routinely use advanced imaging during image-guided radiation therapy to ensure that the radiation accurately targets colorectal cancer while avoiding important organs. This approach helps compensate for changes in the position of organs, such as the bladder or rectum, during treatment. By using image-guided radiation therapy, our doctors are able to target the tumor accurately while reducing the exposure of healthy tissue to radiation.

Types of External Beam Radiation Therapy

Our doctors use several different types of external beam radiation therapy, which are typically delivered by a machine called a linear accelerator. This machine focuses high energy X-rays from multiple angles around the body to deliver radiation that matches the shape of the tumor.

A course of radiation treatment is usually given once daily, five days a week, for one to five weeks. Each treatment typically takes 15 to 20 minutes to deliver.

Our radiation oncologists can discuss which type of radiation therapy and treatment schedule is best for you.

Three-Dimensional Conformal Radiation Therapy

Three-dimensional conformal radiation therapy allows doctors to deliver radiation beams tailored to the size, shape, and location of the tumor. Using a linear accelerator, the oncologist delivers radiation beams aimed from different directions at the cancer. This enables doctors to effectively deliver the therapy to the tumor, while sparing healthy tissue and reducing the risk of side effects.

Intensity-Modulated Radiation Therapy

Intensity-modulated radiation therapy is more targeted than the three-dimensional conformal approach. It allows doctors to divide treatment into many small, computer-controlled beams of different strengths. Together, these beams closely conform to the size, shape, and location of the colorectal cancer.

Using intensity-modulated radiation therapy, doctors are able to adjust the radiation dose within millimeters to spare surrounding healthy tissue. This approach may enable doctors to use higher doses of radiation therapy when needed, while still being able to spare nearby healthy tissue and organs.

Volumetric Modulated Arc Radiation Therapy

Volumetric modulated arc radiation therapy is an advanced variation of intensity-modulated radiation therapy. With this type of radiation therapy, the linear accelerator revolves around you in one or several 360-degree rotations instead of stopping and starting for treatment adjustments. This enables radiation to be given from almost any angle, enabling doctors to more closely target the colorectal cancer while avoiding healthy tissue.


When colorectal cancer has spread to the liver, an interventional radiologist may use radioembolization to deliver targeted radiation directly to cancer cells, sparing healthy cells. In this procedure, tiny beads filled with the radioactive isotope yttrium, or Y-90, are placed into blood vessels that feed a tumor through a catheter that’s inserted into the skin on the arm. The microspheres travel through the bloodstream to the tumor. After several weeks, the radiation decreases and then disappears.

Sometimes, doctors use microwave ablation to destroy colorectal cancer that has spread to the liver. In this procedure, doctors use a CT scan to guide a needle through the skin into a tumor. Next, microwaves are introduced through the catheter to deliver heat that destroys cancer cells. It is performed using general anesthesia.

Minimizing and Managing Side Effects

Common side effects of radiation therapy for colorectal cancer include fatigue, diarrhea, frequent urination, gas, and cramping. Our doctors and cancer center support services can help manage these side effects using integrative medicine therapies at Perlmutter Cancer Center. Our nutritionists can provide dietary guidance after treatments for colorectal cancer.