Radiation damage may cause carotid artery stenosis years after treatment.
By Pamela Tom | HPVANDME Founder
May 2022 marks ten years since my husband, Jeff, underwent radiation and chemotherapy treatment for HPV-related oropharyngeal cancer. I’ve had the privilege of meeting many survivors over the past decade. Their health varies and isn’t quite the same as it was before treatment; however, they are all thankful to be alive.
We live an active live. But last month, things came to a halt—again.
We learned that Jeff had carotid artery stenosis, a narrowing of the neck artery that carries blood from the heart to the brain. Huh? What? We later learned that the radiation he received in 2012 caused stenosis on one side of his neck. His artery: 90% blocked and threatening to cause a massive stroke. Within a week, he underwent urgent surgery to get a stent inserted and open the artery.
After my husband’s cancer, I thought I would never again have to experience the fear that accompanies a serious, potentially fatal condition. Neither our ENT surgeon nor the radiation oncologist advised us to be aware of the possibility of carotid artery stenosis in the future. You may not have heard of it either. That’s why we found out more to share with you.
A Closer Look: Carotid Artery Stenosis
To learn more, HPVANDME spoke with Dr. Daniel Ma, radiation oncologist and Chair of Research in Radiation Oncology at Mayo Clinic in Rochester, MN. Dr. Ma studies novel treatment strategies for reducing the long term, and harsh effects, of radiation treatment for HPV-related head and neck cancer.
The interview has been edited for space.
What is carotid artery stenosis?
“Carotid artery stenosis is a thickening of the artery. The carotid artery is the main artery inside your neck that takes oxygenated blood from your heart to the top of your head and the brain. Usually you see carotid artery stenosis in the setting of cholesterol and plaque forming in older patients. When the carotid artery becomes stenosed or narrowed, you get less blood flow in that area. There’s a possibility that the artery will squeeze down. If that happens, there’s the possibility of developing what we call a TIA, a transient ischaemic attack, or a stroke. It can be temporary or a more serious issue with a lack of blood flow to the brain. Carotid artery issues can be significant.”
Radiation Dosage Matters
The dose of radiation that a carotid artery receives makes a difference for the future development of the stenosis. How often does this occur in HPV throat cancer patients?
“Some of the literature suggests that when the dose of the radiation is at least 40 gray or higher, it causes problems. This can be problematic because the primary dose of radiation that we use for head and neck cancers would be between 60 to 70 gray. This is for for treatment after surgery or treatment without surgery. The studies where they have done ultrasounds on patients, upwards of 50 percent of patients could have detectable differences in the thickness of the walls of the carotid artery. If you compare the side that had radiation versus the side that didn’t have radiation, just because the carotid artery looks significantly different on the ultrasound doesn’t necessarily mean that’s going to be a clinically significant difference.”
How common is carotid artery stenosis in HPV head and neck survivors who have had radiation treatment? More information.
“The carotid artery can also thicken from cholesterol, however the rates of developing more than 30 percent stenosis in the carotid artery can go upwards to around 25 percent in patients who have had 40 to 50 gray of radiation. If you look at rates of having a clinical effect, having a TIA or a stroke after radiation treatment three to five years afterwards, it can be on the order of 10 percent of our (HPV cancer) patients.”
Let’s back up for a minute. Please explain how the radiation dosage is determined. It seems most patients wouldn’t necessarily understand what 40, 50, 60 or 70 gray means.
“Usually radiation therapy is given on a daily basis. The standard dose for daily radiation therapy is treatment at two gray per day. 60 gray of treatment would be 30 days of treatment. If receiving treatment five days a week, that translates to six weeks of treatment. 70 gray is the standard dose of treatment without surgery. That would be 35 days of treatment or seven weeks.”
What Are The Symptoms of Blocked Carotid Artery?
Prevention is the best medicine. Are there symptoms of carotid artery stenosis? What should patients look for? In my husband’s case, he began seeing gray spots then what he described as images resembling a photograph negative. We later learned those were symptoms of mini strokes. More about symptoms.
“It is very challenging. Usually you don’t have side effects from the stenosis. You have carotid arteries on each side of the neck. They have arteries that branch off and provide collateral circulation. If the carotid artery at one point starts narrowing off, there are other areas with blood vessels that will try to compensate to bring blood to those other areas. It’s not until the artery becomes more critically stenosed, will you start having symptoms. One of the early TIA symptoms, if you’re shedding small clots or have restricted blood, is in the vision because those arteries branch out and feed the eye.”
Should My Neck Be Screening Post-Radiation?
Can patients be screened and if so, when? Are head and neck oncologists pushing for a national screening guideline for post-radiation cancer patients?
“There is growing awareness but right now, there is no one national guideline. Our standard recommendation (at Mayo Clinic) is that for patients who are three years out from treatment. We recommend they start having screenings with carotid ultrasounds, so we may have early detection of the thickening of the artery.”
Are you seeing more incidents of carotid artery stenosis now that HPV oropharyngeal cancer survivors are reaching that three to five year mark, or even longer?
“There are many confounding factors when we look at carotid artery stenosis. Many of these are in a patient’s social history, such as smoking and alcohol consumption. These behaviors are traditionally associated with carotid artery stenosis. In previous eras, it was difficult to tease out the contribution from radiation versus smoking versus alcohol. However with HPV-associated patients, they tend to be much younger and non-smokers. We can now see them at a different distribution as they age because the artery also tends to thicken with age. We are also seeing healthier patients with fewer comorbidities for heart disease and carotid artery disease. And they live a lot longer.”
Mayo Clinical Trial Finds Reduced Radiation Doses Effective
For the past ten years, Dr. Ma has been conducting PhaseII/III clinical trials at Mayo Clinic. They are determining if reduced doses of radiation can be effective in fighting cancer. The goal: to lower the dose of radiation in order to reduce the likelihood of harmful side effects from heavier doses of radiation—dry mouth, difficulty swallowing and speaking, and carotid artery stenosis.
In our next blog, we discuss the clinical trial’s findings. Dr. Ma and his team found that a 30 gray dose of radiation over two weeks—half the dose of standard treatments today—are providing successful results with no difference in patients’ overall survival rates.
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