Alberta Cancer Foundation

How radiation therapy works

For medical teams caring for patients with cancer, radiation therapy is a key tool in its treatment. “Cancer is sensitive to it,” says Dr. David Skarsgard, radiation oncologist at Calgary’s Tom Baker Cancer Centre, “and, increasingly, it’s used in conjunction with surgery and chemotherapy.”

About half of all cancer patients will receive some kind of radiation therapy. Its success relies on the way the body normally repairs cellular damage as much as it relies on the way the cancer cells respond to it.

“Radiation deposits energy in the nucleus of a cell, damaging the DNA,” Skarsgard says. “The reason radiation can be effective is because healthy cells can repair themselves, whereas cancer cells can’t do this as efficiently.” Skarsgard says that, in a radical or curative course of treatment, which could take place daily for five to nine weeks, the cancer will fall further and further behind, its self-repair unable to keep up with the damage the radiation is causing, until – hopefully – there is no cancer left.

About half the time, radiation therapy is used palliatively, to treat cancer sites that are causing patients pain or impairing organ function. “For these patients, we aim to improve the quality of life,” Skarsgard says.


Field of beams

A radiation therapist consults an oncologist’s treatment plan and uses a linear accelerator to deliver external beam radiation to a patient. The therapist operates the machine from outside a special room with foot-thick walls designed to protect others from the radiation being delivered to the tumour or the site where the tumour used to be, prior to surgical removal. Curative treatment happens five days a week, over five to nine weeks. Therapists consult the treatment plan and tiny tattoos they have put on the patient’s body to pinpoint the exact site to deliver therapy. Each treatment takes just a few minutes and most patients tolerate it well.


Not a dinosaur species

Brachytherapy, sometimes called internal radiation therapy, happens when oncologists and surgeons place radioactive materials, such as seeds the size of long grains of rice, in the body at the tumour site. The radioactive implants may be temporary, removed after a certain amount of time has passed, or permanent. In the case of some kinds of temporary brachytherapy, patients might be isolated while receiving therapy and they might need to take at-home precautions later, such as avoiding close contact with pregnant women or children. The radiation dissipates over time.


All systems go

Patients take this kind of therapy by swallowing the medicine, via injection or via instillation, in which the medicine is instilled into a body cavity, such as the abdomen. An active ingredient, such as radioactive iodine for example, travels through the patient’s system to kill the cancer. Patients usually have to stay in the hospital in semi-isolation for a few days during this treatment, and take precautions against exposing other people to radiation once they go home. The radiation dissipates over days, until the level of radiation in your body is no longer a potential hazard to others.