I recently had a brain aneurysm treated, the first treatment included stents and coils and had around 2140 mgy of radiation. Recently, about 6 months later I had an angiogram and they saw coil compaction and added more coils, with the second treatment having around 2100 mgy. My question is, from these did I increase my cancer risk significantly?
There are two types of biological risk from radiation that medical physicists focus attention on. One is a potential skin reaction if a large accumulation of radiation impinges upon a region of skin. The other risk is cancer initiated by an accumulation of radiation delivered to radiosensitive organs.
The treatment that you received used a technique called interventional fluoroscopy to produce x-ray images that guided the placement of the stents and coils in your head. The numbers that you were given (2140 and 2100 mGy) is the cumulative air kerma to a reference point from each procedure. The reference point is defined in industry standards and is intended to approximate the location where the x-ray beam first hits the skin. When the skin dose exceeds about 2000 mGy, there is a potential for “transient erythema” which is a temporary reddening of the skin, like a sunburn(1). Since your reported values are just slightly above the 2000 mGy threshold, it is unlikely that you would have experienced erythema because in most cases the x-ray beam is moved around and the dose to any region of skin is less than the reported cumulative air kerma value to the reference point. Therefore the peak skin dose is very likely less than the threshold dose for early transient erythema. However, if you do notice skin changes in the area of your treatment, you should definitely bring it to the attention of your doctor.
The second risk is an increase in the risk of cancer above the baseline risk that every human faces. This risk is difficult to quantify because our knowledge about radiation and cancer is derived from studies of people who received very high radiation doses to their entire body (for example, atomic bomb survivors, nuclear accident survivors, etc.). Applying this knowledge to medical patients who receive localized, smaller doses requires numerous assumptions. It is generally agreed that a radiation dose from medical imaging increases an individual’s cancer risk very slightly above the natural baseline lifetime risk of 42 diagnosed cancers for every 100 people(2). Higher doses are associated with increased risk, but even at the highest doses used in medicine, the overall increase in cancer risk is still quite small compared to baseline and depends on the age and sex of the patient. Using published values for the typical kerma-area product for cerebral neurovascular embolization for aneurysm (250-300 Gycm2)(3), a published dose conversion coefficient from kerma-area product to effective dose (0.087 mSv/Gycm2)(4), and a published cancer risk coefficient(2), a very rough estimate based on many assumptions is that 1 patient in 400 who undergoes cerebral coil embolization may develop a future cancer as a result of the radiation exposure, while about 168 of these 400 will be diagnosed with cancer from other or natural causes. Because of the high natural incidence of cancer in the population, it is impossible to know if an individual’s cancer resulted from a radiation exposure or if it would have occurred anyway.
You had two procedures performed about six months apart. During the time interval between these procedures, your body’s natural DNA repair mechanisms had the opportunity to fix any DNA base pair mutations that may have been caused by the first radiation exposure. We have no way to quantify the degree of repair, but your body did have time to “heal” from the first exposure. For cancer risk, each radiation exposure is considered independent, and the second exposure carries no greater or less risk than the first.
(2) NAS/NRC National Academy of Sciences/National Research Council. Health Risks from Exposure to Low Levels of Ionizing Radiation: Phase 2, BEIR VII, Board on Radiation Effects Research (National Academies Press, Washington), 2006.
(3) Miller et al, Radiation Doses in Interventional Radiology Procedures: The RAD-IR Study Part I: Overall Measures of Dose. JVIR 14(6) 711-727, 2003. https://doi.org/10.1097/01.RVI.0000079980.80153.4B
(4) NCRP Report No 160, Ionizing Radiation Exposure of the Population of the Unites States (National Council on Radiation Protection and Measurements, Bethesda, Maryland), 2009.