What is Radiation Therapy?

Radiation therapy is the treatment of disease, usually cancer, with ionizing radiation. It is typically delivered by a machine called a linear accelerator.

Radiation therapy damages the DNA of cancer cells. This stops cancer cells from dividing and growing, thus slowing or stopping tumor growth. In many cases, radiation therapy is capable of killing all of the cancer cells, thus shrinking or eliminating tumors.

There are several different kinds of radiation therapy. Your radiation oncologist will discuss which kind is best suited to your treatment needs.

Intensity Modulated Radiation Therapy (IMRT)

Intensity Modulated Radiation Therapy (IMRT) is an advanced technique of delivering radiation therapy using complex combinations of radiation beams, and shapes with different (modulated) intensities. This way, the highest intensity of radiation goes to the tumor (or the place where the tumor was removed, also called the tumor bed), enabling a lower intensity to be deposited to surrounding normal tissues.

Typically, intensity-modulated fields come from multiple different beam directions. This produces a radiation dose distribution that is custom tailored to your body. This type of radiation therapy takes a little longer than conventional radiation therapy because of the number of fields and the complex shapes required.

Currently, IMRT is used mainly to treat cancers of the prostate, head and neck, and central nervous system. In some cases it is used to treat breast, thyroid, and lung cancers; gastrointestinal and gynecologic malignancies; and certain types of sarcomas. IMRT may also be used to treat pediatric malignancies.

Image Guided Radiotherapy (IGRT)

Image Guided Radiotherapy (IGRT) is used when targeting accuracy is very critical, or when a tumor moves during and in-between treatments. Breathing, rectum or bladder filling, and swallowing can cause a tumor to move. So can a decrease in tumor size or weight loss. By accounting for tumor motion, IGRT reduces normal tissue exposure to radiation and improves targeting accuracy.

Imaging is usually in the form of external imaging systems (X-rays, ultrasound, optical mapping) or on-board systems (X-ray, cone beam CT, MRI). To assist in visualizing a moving tumor, markers (called fiducials) are often placed inside the body. Fiducials can be gold seeds, coils, or beacons that emit radio signals.

IGRT is often used to treat prostate, head and neck, lung, gastro-intestinal, and gynecological tumors.

3D Conformal Radiotherapy

3D Conformal Radiotherapy uses 3-dimensional representations of the organs to be treated to design the treatment fields. In addition, multiple beam angles can reduce the amount of radiation to normal tissues while concentrating the dose to the target tissues. Computer models of the patient’s anatomy are generated from multiple different imaging sources, such as CT, MR, and PET-CT.

This type of radiation therapy can be used on many tumors, including those in the brain, head and neck, lung, abdominal, pelvic, and skeletal system.