CT technique and technology

This article highlights the wide variation in CT patient radiation dose between similar institutions for similar exams. Recent analysis of ACR dose registry data also suggests there is wide variation amongst different regions of the country.

Such variations suggest that attention to the details of CT technique and technology can produce CT exams at much lower dose – presumably without compromising diagnostic power.

Novel iterative reconstruction method for reducing CT dose

All iterative reconstruction techniques powerfully reduce CT radiation dose in the 40-80% range – without compromising diagnostic power. And they all continue to be refined and to evolve, as this article illustrates. While the “look” of CT images may change from the noise removal, the diagnostic power is not compromised despite the substantial dose reduction. As radiologists, working with change is our future. The old days of nothing but filtered back projection are in our history but not in our future.

CT radiation dose reduction by iterative reconstruction in lymphoma staging

There are some who say that iterative reconstruction should be reserved only for younger patients and not used on older cancer patients who already have serious disease.

But many patients with malignancies are younger or are being treated for cure.

This article suggests that an iterative reconstruction technique (such as model-based iterative reconstruction, MBIR) which can reduce patient radiation dose by 50% may have salubrious utility in patients with lymphomas – who often are younger, who get multiple CT scans, and who are being treated for cure.  

This may apply to other malignancies as well.

Educating patients about radiation dose

The ultimate goal is to have a fully informed and well educated patient – this will result in best personalized healthcare and outcomes.

So as far as radiation dose from individual CT exams is concerned, it is good for patients to know what they received – but it is not enough. Patients also need to be educated about the meaning and risk of their radiation dose.

Educating patients about extremely low risk is difficult – as would be true about any very low risk. But, it should be coupled with educating patients about the potential health and healthcare benefits from their CT exam.

This is because what they really need to know is their risk/benefit ratio – from each CT exam. An educated patient who understands their risk/benefit ratio from CT will be a truly informed healthcare consumer.

Who should educate patients about risk and benefit? All of us – all providers. The primary care physician, the subspecialist, the radiologist, the CT technologist, the radiology nurse, PA’s and LPN’s – everyone who contacts the patient can help advance this education and this understanding.

MDCT 2014 speakers weighed in on this subject at the ISCT Symposium in early June.

Abdominal CT Scans: How Low a Dose is Low Enough?

I was recently asked the question: “How low is low enough for CT?” With the risks of CT scans, the answer is: as low as you can go without significantly compromising diagnostic power.

Sometimes we do very noisy CT exams at extremely low doses, knowing that we may miss a 1 mm ureteral stone. However, we accept that possibility since such a small stone may not be clinically relevant.

Our routine abdominal/ pelvic exam is noisier than most of the CT exams we see referred in – but we deliberately chose to become accustomed to the higher noise levels (even when using  iterative reconstruction) in order to minimize CT radiation dose. Thus, our doses are 40 percent lower than those on some of the CT scans we see being administered at many other places. There is no evidence we have compromised diagnostic power with our reduced dosage CT scans.

In today’s world, the 1-3 mSv cardiac CT is commonplace. In the near future, a CT of the abdomen and pelvis (40 cm of Z axis) using 0.6 mSv will soon be commonplace with the arrival of model based iterative reconstruction. With MBIR recently becoming available in the United States we will soon see dose reductions of up to 80 percent!

Professional Recommendations for Low Dose Optimization

I came across an article from the Journal of the American College of Radiology on a number of recommendations for optimizing patient dose level in chest CT scans, the third most commonly performed CT exam in the country.

As the article points out, the lungs are an ideal organ for low dose radiation CT scans. Some of the recommendations offered include:

  • Doctors should ensure that patients understand all instructions fully, including when to hold their breath and how much movement is permitted.
  • Automated exposure control (AEC) techniques should be used as often as possible to assist with breathing in children and adults.
  • Iterative reconstruction techniques reduce radiation dose exposure substantially and should be performed as often as possible.
  • Centering patients in the gantry isocenter avoids excessive scan length dose. Additionally, CT scans should only be performed on the area of indication.
  • Reading thicker sections ensures CT scan radiation risk reduction, while allowing fine details to be examined in nosier, thicker sections. This procedure should be utilized by imaging professionals.
  • All CT scans should be done for a clinical and justifiable reason.

The tips and pointers in this article are all good tools for lowering patient radiation dose in chest CT. We have found that the use of iterative reconstruction is a big help – lowering dose by as much as 40%. Now that model based iterative reconstruction has recently become available in the USA (GE’s version is called VEO), we can look for dose reductions of more like 80%!

Frequent CT Scanning Not Linked to Cancer Diagnosis

study published in a recent issue of the Journal of American College of Radiology asserts that CT -induced cancers are more likely to occur amongst rarely scanned young adults, as opposed to frequently scanned patients–the group that many assumed was at the highest risk for radiation induced cancer diagnoses.

It is still true that a definite relationship between cancer induction and less than 100 mSv of radiation has never been proven. This is assumed, for safety’s sake – based on proven relationships with much higher doses of radiation. Remember, a typical CT of the abdomen and pelvis in the modern world is about 6-10 mSv.

The other variable that has never been proven is the assumption that the risk from multiple scans which are widely spaced in time is additive. In fact, we know that the body has tremendous capacity to heal and repair any kind of damage – so any damage from a single event of low dose radiation may be fully repaired before a second event occurs. Hence the effect may not be at all additive.

So… results like those found in this article are not surprising.

Nothing, however, should lessen our vigilance about striving for as low a radiation dose as possible for all medical diagnostic imaging applications. In a world of unknowns (and possibly unknowable’s), that’s just common sense.

An Interview with Dr. Mitsumori on Weight-based Selection of CT Parameters

The following is an interview I conducted with Dr. Lee Mitsumori, Assistant Professor of Radiology at the University of Washington.

Dr. Shuman: Please give us a brief overview of your work involving weight-based selection of CT parameters.

Dr. Mitsumori: We have been investigating the use of body-size-dependent CT scan parameters to optimize the radiation dose of each scan. Several imaging parameters can be modified at the time of the CT that can alter the amount of radiation of the scan (tube current, tube potential, scan range, scan phases, image reconstruction techniques). The challenge is to adjust each so that the final set of patient images are of diagnostic image quality and were obtained with the lowest possible radiation dose. The risk is that incorrect settings or too aggressive dose reduction can create a scan that is of poor image quality that does not allow a correct interpretation. Current work at University of Washington Medical Center involves studies comparing different CT image reconstruction techniques (adaptive iterative reconstruction, model based iterative reconstruction) that can significantly reduce CT image noise and how these can be best implemented in patient CT exams.

Dr. Shuman: Why is weight an important concern regarding CT? How does weight affect CT?

Dr. Mitsumori: A patient’s body size, as reflected by weight, affects two important feature of a CT scan. The first is the amount of photons needed to generate an interpretable CT image. A CT is a projection technique, where an x-ray source emits photons that then pass through the subject before being recorded by a detector on the other side of the patient. Larger patients need more photons with higher energy than smaller patients to create images that can be correctly interpreted. If the CT parameters are not correctly set and only a small number of photons are recorded by the detector, the images created are noisy. If an image is too noisy, the interpreting physician may not be able to see if a problem or disease process is present. Unfortunately, the more photons used the higher the radiation exposure of the CT exam. While large patients are at risk for having noisy images, small patients can have scans done with parameters selected for an average sized patient, in which case too many photons are used than what would be needed to create diagnostic images. Thus, the importance of matching the radiation dose (number and energy of photons emitted) with the patient’s body size to prevent non-interpretable studies in larger patients, and avoid excessive radiation dose in the smaller patient.

The second feature of a CT scan where patient size is important is in the amount of iodinated contrast needed for the scan. Iodinated CT contrast is injected intravenously during the scan and improves the depiction of the different organs and vascular structures in the body. With CT imaging, the use of contrast greatly improves the radiologist’s ability to differentiate diseased (tumors, infection, inflammation) from normal tissues. Similar to radiation dose, the amount of contrast needed to enhance the organs is dependent upon patient body size. Small patients will have smaller organs, less blood volume, and be shorter than larger patients. Thus the amount of CT contrast needed may not be the same for every patient.

Dr. Shuman: What are the risks involved when a hospital or imaging center does NOT take a patient’s weight into account?

Dr. Mitsumori: The risks for scanning with fixed CT parameters are that when compared to an average sized patient, the large patient may have scans with noisy CT images that could lead to interpretation errors, or a non-diagnostic scan in which the scan may need to be repeated or an alternative imaging test performed. For the smaller patient, the risk would be that more radiation is used than what is needed to generate adequate, diagnostic images.

Similar risks occur with CT contrast administration. If a fixed amount of contrast is used for every scan that is based on an “average” patient size, then large patients may not receive enough contrast to adequately enhance the internal organs rendering the scan potentially non-diagnostic, and the small patients are given more than the amount of contrast needed to obtain an adequate scan.

Dr. Shuman: When discussing CT exams with their doctors, are there questions a patient should ask regarding their weight? In other words, what would make an “informed patient” as it relates to weight and CT?

Dr. Mitsumori: An informed patient would want to ask if their CT scans will be performed with “patient tailored” or “patient specific” protocols that use the amount of radiation and iodinated contrast that best match the patient’s body size.

Adaptive Iterative Reconstruction Article Featured on Image Wisely

What does adaptive iterative reconstruction do? How is it used?

These are questions addressed in an article of mine featured on the Image Wisely website. As mentioned before on this blog, Image Wisely is an excellent and very useful resource – for both health care providers and patients – that provides information on low dose protocols, radiation risk, and safety in medical imaging.

To read the full article, click here.

ACR Releases Radiation Safety and Medical Imaging PSAs

The American College of Radiology, in an effort to address questions and concerns about radiation risk, has created several public service announcements that inform viewers where they can obtain more information regarding radiation in medical imaging. These PSAs have been released for nationwide broadcast.

The adult-focused version of the announcement directs viewers to the Image Wisely site, while the pediatric version directs viewers to the Image Gently site. Each site individually serves as the primary resource for additional information on imaging and radiation safety.

The PSAs can be found here.

Patient Resource: Radiation Risk Calculator

Here on this blog I often talk about the importance of patient education and awareness, as it relates to CT scans, radiation dose and cancer risks. Informed patients are smart patients! To that end, I wanted to share with you an interesting resource I recently came across: a “radiation risk calculator” sponsored by the American Society of Radiologic Technologists.

According to the site, the purpose of this (free) tool is to “calculate your dose and estimate cancer risk from studies including CT scans, x-rays, nuclear scans and interventional procedures.” I think this is good for patients, if combined with counseling about the meaning of the numbers.

I always say: the more info, the better – as long as it is understood appropriately. Remember too, that a 1 in 2000 risk of causing cancer means a 1999 in 2000 risk of not causing cancer…

The Thyroid Shield Controversy: Cancer Fears Overblown

Recently, an episode of Dr. Oz that linked the increase in thyroid cancer to imaging and biopsy procedures prompted an increase in requests for thyroid shields from women undergoing mammograms. The cancer risk scare appears to be caused by a chain e-mail that was created by a viewer after the episode aired. The public outcry has reached the point that the American College of Radiology and the Society of Breast Imaging have issued a joint statement to try to overcome fears of high radiation risk from mammography.

Here in our own offices, we have women showing up for mammograms bringing their own thyroid shields. This is silly – the amount of scatter radiation is so small as to be hardly measurable with very sensitive instruments.

If you take a thyroid shield to a mammogram, to be logically consistent, you should be wearing it all the time – on any airplane flight, when sunbathing… the list goes on!

Ordering CT scans in the ER: Three Questions

One of the most common complaints of patients in the ER is abdominal pain, and as a recent article at TIME.com details, diagnosis is rarely straightforward. It is important to understand that the ER is different from other places where healthcare is provided. ER physicians see a broad spectrum of disease – from the insignificant to the life-threatening. There are great time constraints in the ER, as well, and follow-up care is hard to arrange (and may be unreliable) so there is pressure for a definitive diagnosis in a single encounter.

Physicians considering the CT scan to assist with diagnosis for abdominal pain or other illness and injuries should consider three questions:

1.  Is CT the right test to do for this patient?

Many ER physicians are good at a answering this question, but it is also helpful to remember that the best expert on appropriate use is one phone call away: the radiologist. Having the patient’s EMR handy is important, too, in reporting how many CT scans this patient may have had historically, since this is a data-point in choosing whether or not to do CT. A national registry of individual patient cumulative radiation dose is coming to the U.S., similar to the one that now exists in the EEU, but it is not here yet.

2.  If CT is the right test, what kind of CT?

With contrast or without? Oral contrast or not? Positive oral contrast or negative? One pass or three? Arterial or portal venous phase? Abdomen only or abdomen plus pelvis? Again, the radiologist is a valuable consultant for getting the most information about the patient’s condition at the least radiation cost.

3.  How can the CT scan be done with the lowest possible radiation dose?

Finally, once the kind of CT exam is decided, how can it be done with the lowest possible radiation dose without compromising the diagnostic value of the scan. A well-informed radiologist can reduce the radiation dose per scan by up to 60 percent. For example, CT of the urinary tract with contrast now can be achieved in a single pass. Careful attention to CT imaging parameters can radically lower dose (low kVp, modulated mA, etc.). Limiting the length of the scan on the patient and careful centering of the patient by the tech can greatly reduce dose. In addition, newer scanners combine better detectors with more complex reconstruction algorithms to substantially lower dose and CT scan radiation risks.

CT Appropriateness Key to Usage, Understanding Risk

A recent study I came across found that patients in emergency departments have very high confidence in CT scans and technology. Furthermore, it seems as if patients get increasingly more confident that they’ll get a proper diagnosis the more testing they have done. But compounding this is another finding of the study: most patients’ understanding of radiation exposure is poor.

The key to this discussion is the concept of appropriateness. What that means is the balance between cost, risk, and the chance that a test may provide valuable information, which impacts on therapy, outcome of the disease process, or peace of mind (which has value, too).

As this study points out, patients have confidence in CT, but that confidence does not translate directly to appropriateness. Risk of CT radiation is hotly debated, but that too does not equate with appropriateness by itself. And cost effectiveness is just one component of the stew that is appropriateness.

So, given all those limitations, how do we get there? Answer: use the radiologist – equipped with powerful support tools – as a consultant to find the balance that optimizes appropriateness. The radiologist is an epicenter of knowledge about radiation risk, cost effectiveness, and the potential positive impact of a CT. Add to that support from a decision support program – which is a compilation of all knowledge in these areas – and you have the best path to appropriateness in this complex world of high-tech imaging.

Do Patients Understand CT Scan Risks?

An article that was published after RSNA talks about a study that found that CT scan radiation risk in patients may be overblown. However, at the close of the article, it says that longer-term, more in-depth study is needed. Until then, physicians and patients still need to weigh the risks and benefits of CT.

For patients to both be informed and to understand (comprehend) risk related to radiation is very challenging. This is because there are few comparables in normal daily life which can clearly quantify extremely small risks. The one I like the most is: 10 mSv give you a risk of dying from an induced cancer of about 1 in 4000. Driving a car in the USA for 80,000 miles over 3 years also gives you a risk of about 1 in 4000 of dying in a car accident.

Now, both a CT scan with 10 mSv and 80,000 miles of use of a car bring certain benefits. But they carry a risk of dying of 1 in 4000. What do you think of that risk/benefit ratio? Would that ratio make you stop driving a car?

Obligation to Patients: Minimize Risk and Maximize Benefit

One of the most exciting – and talked about – sessions at RSNA was called “Radiation Dose: Can It Be Too Low?” The expert panel had a healthy debate on radiation dose and risk, and finally reached an agreement that CT scans should be limited to “justified and optimized studies.” (HealthImaging.com has a good recap of the panel’s discussion.)

The debate about risk can go on, but when practicing medicine (radiology) with real patients, the obligation is to both minimize risk AND maximize benefit.

So the challenge for radiologists is to lower dose as much as possible without compromising the amazing diagnostic power of CT. How to accomplish this is both science and art. But we have discovered at UW that with a combination of low dose technique and low dose CT technology, you can take out up to 40 percent of the radiation dose to the patient (compared to 3 years ago) without having any negative impact on diagnosis. So that number certainly is achievable at most sites.

Could we go even further in dose reduction?

Stay tuned…

Educating Patients About Radiation Risk Not Always Easy

Lots of articles are published on a regular basis that talk about public awareness (or lack thereof) of CT scan risks and benefits. This one’s a recent example. But here’s the thing, which I’ve discovered through personal experience: educating patients about radiation risk is very challenging. This is because extremely low rates of risk are hard to comprehend. It can be talked about in terms of background natural radiation, or risk of driving a car, for example. While it is important that patients be informed, it is also important that they not be scared away from a test that stands a good chance of helping them – a lot. This is a fine balance.

Practicing medicine in an emergency room environment is different from in a clinic or a hospital. The diseases are different as is the acuity. What may not be appropriate in a family medicine clinic population may be appropriate in an acutely ill ER patient.

This is why specialists in radiology and emergency medicine are continually reviewing appropriateness criteria, like those published by the American College of Radiology.

Patients Want To Know About Radiation Risks

A new study published in the November issue of the American Journal of Roentgenology concluded that patients from the emergency department are more concerned about having their condition diagnosed with CT than about the risk of future cancer from radiation exposure.

Although the patients in this study did not estimate the risk of development of cancer as high, the majority of patients wanted someone to discuss the risk and benefits of testing them. This is not as simple as it sounds. How do we best educate patients about radiation? Who is responsible for educating patients about risks and benefits of radiation exposure from CT – the ordering provider, the radiologist, or the CT technologist?

Right now it seems that nobody is doing such education likely due to time constraints and the fact that it is a difficult topic to discuss.  There is no standardized way to discuss radiation with patients and research shows that many physicians don’t fully understand radiation, radiation doses from common tests or possible risks from exposure to radiation from medical imaging. This is a topic that is not going away. We know what our patients want and need, it’s up to us as their healthcare providers to deliver.

CT Perfusion Dose – What is all the Hue and Cry About?

Last year a New York Times investigation uncovered more than 200 radiation overdose cases at Cedars-Sinai Medical Center. According to a New York Times follow-up published on July 31 this year, 200 additional cases were revealed at other hospitals leading to more than 400 cases nationwide. The radiation overdose delivered to patients in these overdose cases was between 4 to 13 times higher than a typical dose for the performed scans. These overdoses led patients to experience hair loss, headaches, confusion, and may increase their long-term risk of cancer and possible eye and brain damage. The patients had received CT brain perfusion exams, which help to identify strokes through a number of blood flow images.

Why did these overdoses happen?  This could be due to equipment malfunction, the need for “prettier” clinical images (requiring high radiation dose), or a serious lack of operator knowledge in setting up the CT imaging protocols for this type of exam. CT brain perfusion is a high-dose exam but can be performed safely if the technologists, physicists and radiologists work diligently together to ensure that the CT imaging protocols are set up optimally to follow the As Low As Reasonably Achievable (ALARA) principle. The dose delivered by this exam should also be monitored on a regular basis to ensure it remains at minimal levels and no equipment malfunction or dose creep has occurred.  Physicians should also be aware of the potential side effects, as discussed above, which can be triggered by such high-dose exams.

Following 2009’s overdose discoveries, the FDA launched a collaborative Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging, to promote the safe use of medical imaging devices, support informed clinical decision making, increase patient awareness, and optimize patient exposure to radiation.

At the recent American Association of Physicists in Medicine (AAPM) annual meeting, the patient safety symposium focused on these overdose cases and the AAPM CT dose summit’s recent efforts to ensure CT scan parameter optimization and patient safety.  The AAPM also produces reports on quality and safety in medical imaging and radiotherapy, along with letter-writing and policy campaigns targeted at the government and public.

Researchers at Mayo Clinic are also investigating the use of new image-processing algorithms to reduce the dose for CT perfusion exams up to 95 percent and maintain the same image quality as a high-dose perfusion exam.

If appropriate steps are taken to ensure patient safety and dose optimization, the benefits from a CT brain perfusion scan far outweigh the risks associated with it.

Debating the Cumulative Radiation Dose Theory

Despite the attention being given to the cumulative CT scan radiation effect and the buzz surrounding risks of repeat CT scans, one leading expert is disputing the theory.

As reported in Diagnostic Imaging, Richard Morin, Ph.D, chair of the American College of Radiology’s safety committee says, “There is no radiation biology to demonstrate CTs are additive in any way.”

Morin uses a driving analogy that relates probability of an accident to the number of miles logged by a driver, but notes that there is not a certain mile threshold, like 200 miles, that would trigger an accident.

I like the driving analogy and used it in my recent post Measuring Risk: Driving vs. CT. Driving is something that most of us can relate to, and therefore the numbers are more meaningful, so I’ve tried to quantify it even further.

Here’s how I like to look at the risk: The risk of dying from a cancer induced from a CT of the abdomen and pelvis in a middle aged male is similar to the risk of dying in a car accident if you drive 36,000 miles – both are about one in 2000.

The debates over cumulative dose theory will continue, and so I feel it’s important to explain the risks in ways people can understand – so that they don’t turn down any life-saving exams out of fear or misunderstandings.

While Dr. Morin explains that there is no way to figure out whether a person developed cancer due to radiation, a carcinogen or chance, he does say “it’s important that the right test is ordered at the right time.”  I’ll add that it’s always a good idea to look at lowering the CT dose, too.

And while the effect of cumulative dose from multiple exams is unproven, we really must take the most conservative position when it comes to public health and assume the effect is cumulative.

Low Dose CT for Cardiac Imaging

Findings of a recent population-based study featured in the Journal of American College of Cardiology (JAAC) suggest cardiac imaging may be putting younger adults at risk due to radiation exposure.

“The study demonstrated that there are sizable rates of radiation exposure for patients 35-54 years, many of whom will likely live long enough for such long-term complications (as malignancy) to potentially develop,” wrote Jersey Chen, MD.

While the results may make cardiologists give further thought to the tests they recommend and alternatives they can use, others point out that the benefits of the test must be weighed against the risks of radiation exposure.

It is very unusual for a patient in this age range to get a cardiac CT scan. But if they do need one, we can now scan them using less than 2 mSv of radiation (compared to 10-25 mSv in 2005).

That means the risk of dying from a cancer induced by the CT scan (1 in 4,000) is about the same as the risk of dying in a car accident if they were to drive 70,000 miles (about 5 years of driving for the average American) which is also about 1 in 4,000.

Keeping Patients Up To Date

Part of doing research at an academic institution requires consenting patients to participate in research studies involving radiation exposure. I’m always amazed at the number of patients that have no idea that their clinically ordered procedure involves radiation, because nobody took the time to explain this. Patients read the papers, they watch the news and they are fully aware of the ongoing media frenzy surrounding radiation in medicine. Patients often ask me, “Is it safe?” While the risk/benefit debate about ionizing radiation exposure continues to be a hot topic in the medical community, we must not forget to keep our patients in the loop.

Educating patients that radiation often is necessary in medicine can be extremely challenging – but it is more critical now than it has ever been. Talking to a patient about radiation exposure is much different than talking to your radiology colleague, especially when the true incremental risk to patients from medical radiation is still under much debate. There needs to be a coordinated effort at each institution to make sure that patients are receiving correct and accurate information about radiation. The imaging community needs to work together to devise websites and reading materials that educate the public about radiation exposure and risks versus benefits of imaging with radiation.  Everyone involved in patient care must understand radiation, radiation risks, alternatives to scanning and what techniques are used to keep dose as low as possible.

Resources on explaining radiation to patients:

1. RadiologyInfo.org

2. “How to Explain Radiation Risk” from the Washington State Department of Health

3. Wanzhen Zeng’s “Communicating Radiation Exposure: A Simple Approach

Is Treatment Necessary? Ask a Radiologist.

In a recent New York Times article, Dr. Peter Libby, chief of cardiovascular medicine at the Brigham and Women’s Hospital in Boston, discusses the benefits versus the risks and costs of medical procedures like CT scans. In particular, he addresses the issue of incidentalomas, which occur when “medical scans pick up incidental findings that may be benign, leading to complications that make an otherwise healthy person ill.”

Dr. Libby writes, “While contemporary imaging modalities offer powerful and much needed tools for diagnosis and management when appropriately deployed, we should bear in mind the potential risks they entail if used indiscriminately.”

The problems created by incidentalomas is one area where you really need an expert: your radiologist.

This is what radiologists do – they don’t merely detect findings on CT scans, but also attach significance (or insignificance) to each finding.

When all your training and all your experience is in CT scans and their findings, you become pretty good at telling incidentalomas from true problems which need more investigation. Not perfect, of course, but pretty darn good.

Measuring Risk: Driving vs. CT

In the past couple weeks there has been much talk about the cancer risk from medical radiation. According to a recent Reuters article, one chest CT scan delivers the same radiation (and risk) as 100 chest X-rays. However, these numbers still do not communicate the bigger picture: CT cancer risk can be more clearly explained.

Since most people never get close to getting 100 chest X-rays, we need to find a more common point of comparison. Driving, however, is something most North Americans do on a regular basis, and its risks are well-publicized.

43,000 people died in 2007 from car accidents in the U.S. During that same year, U.S. drivers drove 3 trillion miles, according to the U.S. Census Bureau. Based on these statistics, the risk of dying from driving 35,000 miles is about 1 in 2000 (0.05%).

An abdominal/pelvic CT scan delivers about 15 milliSieverts of radiation. In our calculations, using the most conservative data from the atomic bombings of Hiroshima and Nagasaki and the Chernobyl disaster, the risk of mortality from radiation-induced cancer is also about 1 in 2000 (0.05%).

Published data also supports this risk level: Brenner and Hall have estimated that the total lifetime attributable risk of death from cancer after receiving an abdominal CT with 240 mAs, is in the 0.06%-0.07% range (this estimate is for ages 15-25; CT risk drops radically after age 25).

Thus: If the average U.S. driver travels just under 14,000 miles per year… then the risk of dying in car accident (if only driving for 2 years, or 35,000 miles) is about the same as the lifetime risk of dying from cancer induced by the radiation in a CT of the abdomen and pelvis.

Of course, driving more carefully and lowering the CT dose per scan both are good ideas.

Standardization Protocols for CT Would Help Lower Dose, Increase Patient Safety

Last month, the American Association of Physicists in Medicine (AAPM) hosted national Dose Summit that focused on the need for standardization protocols for CT scanning, which would help to ensure patient safety and lower associated radiation risks during CT exams.

According to an e! Science News article, summit attendees included some of the world’s leading experts in CT imaging. Organizer Cynthia McCollough, Ph.D., said the summit “achieved its goal of identifying several issues that need to be dealt with by the medical imaging community in order to address the safety concerns of patients at U.S. hospitals and clinics.”

This summit also made progress in “developing consensus CT protocols and making them freely available via the Internet to hospitals and clinics across the United States.” CT protocols (or “imaging parameters”) define how equipment is used for certain procedures.

In my opinion, standardization of protocols is a powerful way to lower CT dose. In a recent study published in the Annals of Internal Medicine, adjacent hospitals in the San Francisco Bay area had a 13-fold difference in CT exam radiation dose for similar studies done for similar indications. The difference was all in the technique parameter selection.

With standardized protocols, groups of radiologists can get together to study how to do various types of CT exams with the lowest dose but yet still producing good diagnostic information. Once they agree on CT technique parameter selection with low dose as a goal, they can all use the same protocols and practices. This can dramatically lower the dose to a patient population – through standardization on best practices in CT.

CT Radiation Risks Outweighed When Preventing, Guiding Acute Appendicitis Surgery

One of the largest studies to date has confirmed the accuracy of CT scans for acute appendicitis in adults, which supports the use of CT for diagnostic and surgical means when risk for radiation exposure is low, according to findings published in a recent AuntMinnie.com article.

Dr. Perry Pickhardt, professor of Radiology at the University of Wisconsin, said that “at least three other studies confirmed that the negative appendectomy rate dropped from more than 20 percent to less than 10 percent with the use of CT… but one thing that was lacking was the actual diagnostic performance or accuracy with MDCT… so we looked at what I think is the largest CT-based cohort for appendicitis.”

Dr. Pickard presented this data at the International Society for Computed Tomography (ISCT) meeting I just attended in San Francisco.

This is a very good example of how CT can accurately prevent surgery when it is not needed while also guiding correct surgery when it will do a lot of good. In this application, CT is cost-effective and does a lot of good – way outweighing any (very low) risk from the radiation. For adults it is the diagnostic exam of choice in situations where signs and symptoms raise concern about possible appendicitis.