CT Radiation and Cancer Risk
Hello. I'm Dr. David Johnson, Professor of Medicine and Chief of Gastroenterology at Eastern Virginia Medical School. Welcome back to another GI Common Concerns -- Computer Consult. Today I want to talk to you briefly about issues in radiation exposure.
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As healthcare providers, we order a lot of tests. We order tests to accelerate a diagnosis, sometimes to provide a definitive answer.
We have come a long way in radiologic imaging since 1972 when CT scans were first introduced. We tend to rely on this diagnostic test in an immeasurable way in almost everything we do in medicine.
I worry that every patient who goes through the emergency room gets a CT scan. Patients get CT scans for everything from sneezing and wheezing to bleeding and abdominal pain. CT scans are performed routinely, especially in the emergency room.
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It is estimated that approximately 60 million CT scans are done annually in the United States. These scans account for 60%-70% of the ionizing radiation used in radiologic imaging in the United States at the present time.
Now, why is that important?
CT scans or any imaging that involves ionizing radiation poses risks. Radiation exposure has untoward effects. We know that from 2 large databases.
One of these is the Nagasaki-Hiroshima database that followed survivors after the atomic bomb, and the other is radiation workers who were followed sequentially. On the basis of dosimetry, the exposures of radiation workers were very much in parallel with patients exposed to the atomic bomb. An incremental cancer risk was found when compared with the natural cancer incidences, using the Surveillance Epidemiology and End Results (SEER) database. These individuals had incremental risks for cancer over their post-exposure lifetimes.
[ CLOSE WINDOW ]
(Enlarge Slide)
Why does that occur? Radiation does 2 things.
It has an immediate effect, known as a deterministic effect, and we see that in medical oncology when patients are given radiation to kill cancer tissue. With a deterministic effect, radiation induces immediate cell death.
Ionizing radiation for diagnostic purposes induces a stochastic effect; it induces changes to the cellular genome. This may take years or even decades before it is transformed into a potential consequence. We know that there are consequences, and we know from the radiation health workers and the atomic bomb survivors that risks increase as radiation exposure exceeds a threshold, or a certain defined limit.
[ CLOSE WINDOW ]
(Enlarge Slide)
If radiation exposure exceeds a threshold of 5 millisieverts (mSv), the risk for cancer increases over the general risk in patients who were not exposed to that dose of radiation.
The typical abdominal CT scan exposes the patient to 5-10 mSv of ionizing radiation. If the patient is obese, the dose of radiation is doubled as a result of the need for greater penetration. The patient is already in the 10- to 20-mSv dose range, far beyond the threshold of 5 mSv, and the radiation cancer risk goes up from there. Remember that radiation is cumulative.
Most patients who have 1 CT scan will receive a second scan sometime during their lifetime, not just for screening purposes but for diagnostic purposes.
The relative risk for cancer in the United States right now attributed to radiation-induced cancer is 2%-3%. Of all cancers, 2%-3% are attributed to iatrogenic radiation exposure.
[ CLOSE WINDOW ]
(Enlarge Slide)
If you take this to an individual patient level, a single CT scan in a 25-year-old provides an incremental lifetime risk of about 0.6% for death from cancer. In a 50-year-old patient, that risk declines; the numbers go down by about 60%, but it's still a relative risk that's carried forward for the rest of life. If we consider procedures that involve a lot of radiation, such as coronary angiography, the lifetime risk for a 25-year-old woman developing breast or lung cancer is 1 in 143. That's a lot of risk.
Patients are becoming more aware, and Congress has recognized that radiation exposure is something that needs to be tracked. The US Food and Drug Administration has for a long time labeled radiation, and even ionizing radiation from diagnostic imaging, as "carcinogenic."
This is a real problem. Do we think about this when we order tests? Probably not. Should we be thinking about it? Yes. Who's keeping track of this for our patients? Some patients are saying, "You know, I had that test a year ago. Do I really need it again?"
[ CLOSE WINDOW ]
(Enlarge Slide)
Think about the patients who come in for abdominal pain, the patients who have kidney stones, patients with inflammatory bowel disease, and the pediatric patients. Many of these patients have sequential scans throughout their lifetime. We are building a risk for carcinomas that we didn't really intend. We're just trying to do a diagnostic study to evaluate for some type of etiology or pain.
Do we have any medico-legal risk? This issue has not been raised yet, but we should start thinking about it.
There is case law that goes back to the early 1970s: Canterbury v. Spence. The decision was that, for reasonable decision-making, the provider needs to discuss with the recipient of care any information that may influence whether that recipient would be willing to undergo the test. That involves assessment of risk, beyond the risk of not doing the test, but the risk of doing the test.
[ CLOSE WINDOW ]
(Enlarge Slide)
Now, with x-rays we don't really explain this to patients very well. We certainly don't sit down and say, "You know if I order this test, your incremental exposure here is 10 mSv, or is 60 mSv. Do you realize what that means for your lifetime risk for cancer?" This is a concern. Certain countries have outlawed radiation use for screening purposes. In Europe, most notably in Germany and Switzerland, you cannot do a screening test that involves radiation exposure.
Then, we start to think about things like CT colography and virtual colonoscopy. We must start to ask the question: do we really want to take an incremental risk of radiation over the relative risk that we have for other diagnostic tests?
Take a moment to discuss with the patient, "How many of these scans have you had before?" Consider their "running tallies" of radiation exposure. Patients need to be more proactive. Providers need to be more proactive as well because most providers have been relatively clueless about this.
It's time for real paradigm shift on use of ionizing radiation. It's wonderful for imaging, but is it wonderful for the lifetime of the patient?
[ CLOSE WINDOW ]
(Enlarge Slide)
Remember, rule number one is to do no harm. Start to ask the questions: "How many of these have you had? Do I really need to do a test that involves ionizing radiation? Maybe I can use an ultrasound or an MRI if a test is really needed."
Be particularly sensitive to patients when you're ordering tests for a younger age group, children in particular, and patients who are subject to lifetime exposure to radiation going forward because of their underlying disease and their need for repetitive testing in the future.
I know we can do better, and I'm counting on you to do what I am doing in my practice, looking for alternative means to achieve the same ends.
I hope this gives a moment of pause the next time you start to write the prescription for a test involving radiation exposure. I'm Dr. David Johnson. Thanks for listening. I look forward to seeing you again soon.
The Use of Radiologic Imaging
Hello. I'm Dr. David Johnson, Professor of Medicine and Chief of Gastroenterology at Eastern Virginia Medical School. Welcome back to another GI Common Concerns -- Computer Consult. Today I want to talk to you briefly about issues in radiation exposure.
[ CLOSE WINDOW ]
(Enlarge Slide)
As healthcare providers, we order a lot of tests. We order tests to accelerate a diagnosis, sometimes to provide a definitive answer.
We have come a long way in radiologic imaging since 1972 when CT scans were first introduced. We tend to rely on this diagnostic test in an immeasurable way in almost everything we do in medicine.
I worry that every patient who goes through the emergency room gets a CT scan. Patients get CT scans for everything from sneezing and wheezing to bleeding and abdominal pain. CT scans are performed routinely, especially in the emergency room.
[ CLOSE WINDOW ]
(Enlarge Slide)
It is estimated that approximately 60 million CT scans are done annually in the United States. These scans account for 60%-70% of the ionizing radiation used in radiologic imaging in the United States at the present time.
What Are the Risks of Radiation?
Now, why is that important?
CT scans or any imaging that involves ionizing radiation poses risks. Radiation exposure has untoward effects. We know that from 2 large databases.
One of these is the Nagasaki-Hiroshima database that followed survivors after the atomic bomb, and the other is radiation workers who were followed sequentially. On the basis of dosimetry, the exposures of radiation workers were very much in parallel with patients exposed to the atomic bomb. An incremental cancer risk was found when compared with the natural cancer incidences, using the Surveillance Epidemiology and End Results (SEER) database. These individuals had incremental risks for cancer over their post-exposure lifetimes.
[ CLOSE WINDOW ]
(Enlarge Slide)
Why does that occur? Radiation does 2 things.
It has an immediate effect, known as a deterministic effect, and we see that in medical oncology when patients are given radiation to kill cancer tissue. With a deterministic effect, radiation induces immediate cell death.
Ionizing radiation for diagnostic purposes induces a stochastic effect; it induces changes to the cellular genome. This may take years or even decades before it is transformed into a potential consequence. We know that there are consequences, and we know from the radiation health workers and the atomic bomb survivors that risks increase as radiation exposure exceeds a threshold, or a certain defined limit.
[ CLOSE WINDOW ]
(Enlarge Slide)
If radiation exposure exceeds a threshold of 5 millisieverts (mSv), the risk for cancer increases over the general risk in patients who were not exposed to that dose of radiation.
The typical abdominal CT scan exposes the patient to 5-10 mSv of ionizing radiation. If the patient is obese, the dose of radiation is doubled as a result of the need for greater penetration. The patient is already in the 10- to 20-mSv dose range, far beyond the threshold of 5 mSv, and the radiation cancer risk goes up from there. Remember that radiation is cumulative.
Most patients who have 1 CT scan will receive a second scan sometime during their lifetime, not just for screening purposes but for diagnostic purposes.
The relative risk for cancer in the United States right now attributed to radiation-induced cancer is 2%-3%. Of all cancers, 2%-3% are attributed to iatrogenic radiation exposure.
[ CLOSE WINDOW ]
(Enlarge Slide)
If you take this to an individual patient level, a single CT scan in a 25-year-old provides an incremental lifetime risk of about 0.6% for death from cancer. In a 50-year-old patient, that risk declines; the numbers go down by about 60%, but it's still a relative risk that's carried forward for the rest of life. If we consider procedures that involve a lot of radiation, such as coronary angiography, the lifetime risk for a 25-year-old woman developing breast or lung cancer is 1 in 143. That's a lot of risk.
Patients are becoming more aware, and Congress has recognized that radiation exposure is something that needs to be tracked. The US Food and Drug Administration has for a long time labeled radiation, and even ionizing radiation from diagnostic imaging, as "carcinogenic."
This is a real problem. Do we think about this when we order tests? Probably not. Should we be thinking about it? Yes. Who's keeping track of this for our patients? Some patients are saying, "You know, I had that test a year ago. Do I really need it again?"
[ CLOSE WINDOW ]
(Enlarge Slide)
Think about the patients who come in for abdominal pain, the patients who have kidney stones, patients with inflammatory bowel disease, and the pediatric patients. Many of these patients have sequential scans throughout their lifetime. We are building a risk for carcinomas that we didn't really intend. We're just trying to do a diagnostic study to evaluate for some type of etiology or pain.
Medico-Legal Concerns for Clinicians
Do we have any medico-legal risk? This issue has not been raised yet, but we should start thinking about it.
There is case law that goes back to the early 1970s: Canterbury v. Spence. The decision was that, for reasonable decision-making, the provider needs to discuss with the recipient of care any information that may influence whether that recipient would be willing to undergo the test. That involves assessment of risk, beyond the risk of not doing the test, but the risk of doing the test.
[ CLOSE WINDOW ]
(Enlarge Slide)
Now, with x-rays we don't really explain this to patients very well. We certainly don't sit down and say, "You know if I order this test, your incremental exposure here is 10 mSv, or is 60 mSv. Do you realize what that means for your lifetime risk for cancer?" This is a concern. Certain countries have outlawed radiation use for screening purposes. In Europe, most notably in Germany and Switzerland, you cannot do a screening test that involves radiation exposure.
Then, we start to think about things like CT colography and virtual colonoscopy. We must start to ask the question: do we really want to take an incremental risk of radiation over the relative risk that we have for other diagnostic tests?
Take a moment to discuss with the patient, "How many of these scans have you had before?" Consider their "running tallies" of radiation exposure. Patients need to be more proactive. Providers need to be more proactive as well because most providers have been relatively clueless about this.
Time for a Paradigm Shift?
It's time for real paradigm shift on use of ionizing radiation. It's wonderful for imaging, but is it wonderful for the lifetime of the patient?
[ CLOSE WINDOW ]
(Enlarge Slide)
Remember, rule number one is to do no harm. Start to ask the questions: "How many of these have you had? Do I really need to do a test that involves ionizing radiation? Maybe I can use an ultrasound or an MRI if a test is really needed."
Be particularly sensitive to patients when you're ordering tests for a younger age group, children in particular, and patients who are subject to lifetime exposure to radiation going forward because of their underlying disease and their need for repetitive testing in the future.
I know we can do better, and I'm counting on you to do what I am doing in my practice, looking for alternative means to achieve the same ends.
I hope this gives a moment of pause the next time you start to write the prescription for a test involving radiation exposure. I'm Dr. David Johnson. Thanks for listening. I look forward to seeing you again soon.
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