Why Do I Sometimes Feel Tired After Radiation Therapy?

May 22, 2017

radiation therapy, radiation oncology
Radiation therapy works by destroying diseased, cancerous tissue – creating a “wound” that sparks an immune response.

One of the most common side effects cancer patients experience is fatigue. During treatment, some patients may feel particularly tired after receiving radiation therapy.

Fatigue can result when the immune system responds to an injury or wound. This occurs because the immune system uses energy to fight infection and sends out substances that make the body want to rest so it can heal. A bad scrape on the arm, for example, triggers an immune response that causes the site of the wound to become inflamed and can produce some general fatigue. Radiation therapy works by destroying diseased, cancerous tissue – creating a “wound” that sparks a similar immune response.

The amount of fatigue produced by radiation therapy varies with the part of the body being treated, says Anthony D’Amico, MD, PhD, chief of the Division of Genitourinary Radiation Oncology at Dana-Farber/Brigham and Women’s Cancer Center.

If radiation is delivered to the brain, which controls awareness and overall energy, the resulting swelling often produces significant fatigue. Radiation directed at the prostate – an acorn-sized gland – is likely to produce much less. A middle example would be rectal cancer, where radiation reaching the bone marrow in the hips could lead to a general feeling of fatigue.