Low dose radiation can potentially increase the risk of strokes, although this risk is complex and depends on several factors including the dose, duration, and location of exposure. Radiation, even at relatively low doses, can cause damage to blood vessels, particularly the carotid arteries, which are crucial for supplying blood to the brain. This damage can lead to a condition called radiation-induced carotid artery stenosis, where the arteries narrow due to injury and inflammation, increasing the risk of ischemic strokes.
The mechanism behind this involves ionizing radiation causing injury to the endothelial cells lining the blood vessels. This injury triggers inflammation, thickening of the vessel walls (intimal hyperplasia), death of the middle layer cells (medial necrosis), and fibrosis of the outer layer (adventitial fibrosis). These changes accelerate the development of atherosclerosis, a process where plaques build up inside arteries, narrowing them and reducing blood flow. Even doses as low as 10 Gray (Gy) have been associated with increased risk, suggesting there may not be a completely safe threshold for radiation exposure to the carotid arteries.
Radiation-induced damage to the carotid arteries often develops slowly and may remain asymptomatic for years. When symptoms do appear, they can include transient ischemic attacks (TIAs), which are brief episodes of stroke-like symptoms, or full ischemic strokes. In some cases, radiation can also impair the baroreceptors—specialized sensors in the carotid artery walls that help regulate blood pressure—leading to blood pressure instability and further cardiovascular risk.
The risk of stroke from low dose radiation is particularly relevant for patients who have undergone radiation therapy for head and neck cancers, where the carotid arteries may be exposed. Studies have shown that about 21% of patients receiving radiation therapy develop significant carotid artery narrowing within a few years, and 5-10% may experience stroke or TIA over a longer period.
Outside of therapeutic radiation, low dose radiation exposure from diagnostic imaging, such as CT scans, is generally much lower and the associated stroke risk is less clear. However, there is evidence that repeated or cumulative low dose radiation exposure may have subtle effects on vascular health. The linear no-threshold model, which is often used to estimate radiation risk, assumes that even the smallest dose carries some risk, but this model is debated and the actual risk at very low doses remains uncertain.
In occupational settings, such as for interventional cardiologists who are exposed to low levels of radiation over many years, there is concern about cumulative vascular and other health effects, but direct links to stroke risk are not well established. Protective measures, like lead shielding, are important to minimize exposure.
In summary, low dose radiation can increase stroke risk primarily through damage to the carotid arteries leading to accelerated atherosclerosis and impaired vascular function. This risk is most significant in patients exposed to radiation therapy near the neck region. For lower doses from diagnostic imaging or occupational exposure, the risk is less clear but may still exist, especially with repeated or prolonged exposure. Monitoring and protective strategies are important to reduce potential vascular complications from radiation.