Ionizing radiation exposure

What it is

Ionizing radiation exposure — particularly previous radiation therapy directed at the head (for example, to treat a prior cancer) — is the best-established environmental risk factor for developing a glioma. The increased risk typically applies years after the exposure.

Understanding Ionizing radiation exposure

Among the many factors studied as possible glioma causes, ionizing radiation to the head is the most firmly established. People who received cranial radiation therapy in the past — such as childhood treatment for leukemia or other cancers — have an increased risk of developing brain tumors, including gliomas, often years to decades later. This is a recognized example of a "secondary" tumor caused by prior treatment. Importantly, this refers to therapeutic (high-dose, medical) radiation, not the low-dose radiation of routine diagnostic imaging, and it accounts for only a small fraction of gliomas overall. The benefits of necessary radiation therapy generally outweigh this long-term risk, which is one reason radiation is used carefully and avoided when possible in young children. Understanding ionizing radiation and gliomas clarifies the best-established environmental risk factor.

Why it matters

Understanding ionizing radiation and gliomas helps patients and families see the one well-established environmental risk factor — prior radiation therapy to the head — while recognizing it accounts for only a small fraction of gliomas.