Optimizing CT Radiation Doses Across Institutions Leads to Dose Reductions

This excellent research from UCSF documents that education about best CT dose practices has a significant impact. The authors state, “The project strategy was to collectively define metrics, assess radiation doses, and move toward dose standardization. This article presents the results of our efforts using a combination of facility-level audit and collaborative efforts to share best practices.”


New National Dose Levels Established for Common CT Exams

Dr. Kanal’s Research Establishes New National Dose Levels for Common CT Exams

Kalpana M. Kanal, Ph.D., a medical physicist, professor and section chief in diagnostic physics in the Department of Radiology at the University of Washington School of Medicine, Seattle, and colleagues examined actual patient data from the American College of Radiology (ACR) CT Dose Index Registry to develop size-based DRLs that enable healthcare facilities to compare their patient doses with national benchmarks and more effectively optimize CT protocols for the wide range of patient sizes they examine.

The use of DRLs have shown to reduce overall dose and the range of doses observed in clinical practice.

Dr. Kanal’s research is published here in Radiology.

This landmark work is very helpful in benchmarking CT dose levels. It will be widely cited, I predict. Congratulations, Kalpana!

Kalpana M. Kanal, Ph.D.

Adopting Best Practices for CT Radiation Dose Monitoring

In this article, the research conducted by University of Washington Radiology Fellow Dr. Achille Mileto and colleagues highlight the importance of dose monitoring, but also the challenges: “Successful efforts to reduce overall radiation doses may actually direct attention away from other critical pieces of information that have so far been underappreciated, namely the widespread variability in global radiation dose values across clinical operation volumes.” … “These data may provide a foundation for the future development of best-practice guidelines for patient-specific radiation dose monitoring.”

Dr. Achille Mileto from the University of Washington

“We are kind of obsessed with radiation dose reduction, but I think we should keep in our minds the concept of radiation dose optimization, which means trying to adjust the dose to the specific clinical task,” Mileto said. “With technology we are reducing the dose, but we are increasing the room for variability. This is great if you are consistently reducing the dose, but we really want to understand what’s going on in terms of variability. So I think the main lesson is to try to develop best-practice guidelines for patient-specific radiation dose monitoring. I think basically the scenario in the near-term future will be to create some kind of shared library for radiation doses.”

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.

The effect of trauma backboards on CT radiation dose

This article provides another neat bit of knowledge to consider when looking for lowest dose – though this is multi-factorial.

[Excerpt below]Backboard use in ED Figure 6

“Rate of backboard use during CT examinations of the chest–abdomen–pelvis performed in the ED from 1 January 2010 to 31 December 2012 (n=1532). Note the dramatic drop in backboard use in 2011 after multidisciplinary implementation of a policy for prompt removal of patients from backboards using primary clinical survey rather than waiting for a CT examination.”

Reducing dose for CT pulmonary angiography

Paying attention to limiting Z axis coverage yields big dose saving dividends! See this article for results of this study designed to assess the safety and efficacy of radiation dose reduction in hospitals lacking iterative reconstruction.

Low dose CT Revolution scanner

Seattle King5 TV’s Jean Enerson reported recently on UW Medical Center’s installation of the GE Revolution CT scanner.

Revolution CT scanner

The new technology of the Revolution features the following:

  • Much longer and wider detector
    • (16 cm vs. 4 cm)
  • Much faster rotation speed and scanning
    • (0.28 seconds – 70 G’s centrifugal force)
  • Much better radiation dose lowering technology
    • ASIR-V, auto kVp, density modulated auto mA

16 cm wide-detector array: Whole organ scanning on one 0.2 second rotation

Currently, the Revolution CT scanner is being used at UW Medicine for scans of the heart, blood vessels, and organs that involve more than one pass and the evaluation of transplanted organs. In the future, we intend to expand further into:

    • TAVR
    • All aortograms
    • Cardiac
      • coronaries, perfusion, congen., ablation
    • All misc. vascular studies
      • Renal arteries, HA, runoffs, carotids, COW, grafts/stents, venograms
    • Non-Dual-Energy multi-pass exams
      • Liver, pancreas, IVP
    • Perfusion (brain, transplants, tumor)
    • Workhorse (CAP, KUB, brain, spine)


Annual screening for lung cancer low-dose CT

This is a major advance as American healthcare evolves from reactive to preventive.

But a key to success in this lung cancer screening program is keeping the radiation dose of each exam as low as possible – certainly well below one mSv. Ideally, a low dose approach would involve model based or some other form of iterative reconstruction. All the other techniques to minimize dose should be employed together. Fortunately, this is an application where very low kVp will work well (70-100).

Next – and possibly even more impactful: coverage for screening CT colonography.

Radiation protection shielding

This article outlines the substantial reduction in radiation exposure to body parts which are shielded during a CT scan but not included in the field of imaging.

That is a very good practice.

More controversial is another practice: shielding sensitive body parts which ARE included in the field of imaging, specifically breasts, thyroid and gonads.

For some types of scanners this works well, while for other types less well.

With our scanners (GE) IF shielding to the sensitive body part is applied after the scout views are obtained, and IF the shield is separated from the body by placing towels or a blanket to elevate the shield off the body by 2-3 cm – then this works well. Any artifacts or other issues with image quality are minimal or out of the area of interest and the dose to the shielded body part does drop measurably.

Further, such shielding sends a strong message to patients and to our own staff about our concern for their safety.

Reducing radiation dose in diagnostic CT of the abdomen

Here’s a neat trick for dose reduction in appendicitis CT cases – which often are done in young patients.

It falls into the general category of only scanning as much Z-axis length as is needed to address a given indication –  and no more.

Lowering radiation dose without affecting diagnostic confidence

Guest blog by Kalpana M. Kanal, PhD, Director of Diagnostic Physics Section and Associate Professor in the Department of Radiology at University of Washington

How low can we go in radiation dose without affecting diagnostic confidence for detection of low-contrast liver lesions?

In a recent article we published, we studied the impact of incremental increases in CT image noise on detection of low-contrast hypodense liver lesions. Clinical CT liver exams were obtained on a 64-slice CT scanner using automatic tube current modulation at a routine clinical noise index 15.   An artificial image noise addition tool was used to increase the noise level in clinical liver CT images to simulate 75% (NI 17.4), 50% (NI 21.2), and 25% patient radiation dose (NI 29.7) scanning relative to the original images (NI 15.0; 100% dose).  The images were reviewed by radiologists of varying experience who subjectively scored lesion detectability on all the images, original and simulated.

We concluded that there is little loss of detection sensitivity for low-contrast liver lesion detectability of CT exams scanned with a NI at least up to 21.2 compared to a NI of 15, a patient radiation dose reduction of 50%. No significant degradation was observed when reader performance was evaluated as a function of lesion size (>10 mm) and contrast (>60 HU) at 90% sensitivity.  When lesion size dropped to <10 mm or contrast was <60 HU, sensitivity did drop to 85%.

This study had some limitations, the most important of which was that this study was a simulation and not a true study of CT scanning at lower radiation dose compared to high dose scanning which would have involved scanning patients multiple times. Nevertheless, this study was important as it demonstrated that dose could be reduced by 50% without affecting diagnostic confidence for detecting low-contrast liver lesions.

Impact of education and awareness on reducing radiation dose

Guest blog by Kalpana M. Kanal, PhD, Director of Diagnostic Physics Section and Associate Professor in the Department of Radiology at University of Washington

In a recent article, radiation dose was dramatically reduced when technical changes combined with radiation safety initiatives were implemented for adult and pediatric patients undergoing procedures in a cardiac catheterization lab. The air kerma was compared between the first year and the final year of the study. Radiation safety initiatives such as formation of a safety committee, dose reporting and fellow training were implemented into the practice along with technical changes such as reduced dose rates and removal of grid for smaller patients. Considering all procedures, the air kerma decreased by 61% which was significant. For pediatric patients in age range 10-17, the air kerma decreased by 74% which is important as these patients are at higher risk than adults.

This study is important as the patients undergoing cardiac catheterization procedures typically receive high doses and are also potentially repeat patients.  This study demonstrated that increased provider awareness combined with radiation safety initiatives, education and technical changes does have an impact on reducing radiation dose.

A thoughtwise approach to CT iterative reconstruction

This very wise philosophy for implementing iterative dose reduction in any CT program was well presented at the recent MDCT meeting of the ISCT in San Francisco in June. A key component is to have regular and measurable ways for radiologists to regularly grade or score image quality as dose is ramped down slowly with increasing amounts of iterative reconstruction. With Model Based Iterative Reconstruction (MBIR), it may be possible to drop dose up to 60% compared to otherwise low dose adaptive statistical iterative reconstruction methods (ASIR) – but not in one jump. It takes time to get accustomed to the slightly different look of images with iterative reconstruction.

At least a month’s worth of experience should accrue before passing judgment on image quality. It is also important to guard against anecdotal cases used to render judgments, so experience over time is important. But with a methodical approach, a lot of progress can be achieved in overall dose reduction.

Low-dose CT technique in diagnosing Crohn’s disease

Patients with Crohn’s disease often are young and often have their disease activity assessed repeatedly with CT – though MR is used more frequently now as well.

So – they are good candidates for reducing radiation dose by means of iterative reconstruction.

This paper demonstrates that considerable reduction of dose can be achieved without damaging image quality.

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.

Lowering medical radiation dose with CT and other modalities in cancer patients

It is often said that radiation from diagnostic imaging is not an important issue in cancer patients.

But this report suggests otherwise – as expressed by oncologists.

Many patients with cancer are young and/or are being treated for cure. Many have long life expectancies despite having cancer.

And the basic principal of “Do no harm” plus that of ALARA still apply – as much to cancer patients as to any other patient with a serious disease.

So we should be striving for maximal diagnostic information from minimal radiation dose with CT and other modalities in cancer patients, too.

Get Started! Steps for Implementing Dose Reduction Programs.

At a recent Society for Pediatric Radiology (SPR) meeting in San Francisco, one presentation addressed low-dose CT’s “bright future, but troubled present.” Texas Children’s Hospital’s Dr. R. Paul Guillerman touched on the many uncertainties and challenges involved in low-dose radiation optimization, citing that these goals are so complex that they may nearly be impossible.

But, let’s take another look at this. Yes—dose reduction is complex and full of potential traps leading to poor technique or image quality. However, that is not a reason to avoid implementing a dose reduction (technique optimization) program at your institution!

So, how do you lead your institution down a road towards dose reduction? First, start with Google. Read what you can find on the topic. Then, go to meetings, talks, and presentations given by experts with considerable experience in the endeavor. Finally, start at your own institution.

I would suggest trying one variable at a time. Implement a weight based (or cross-sectional area based) kVp selection program. Then, embark on understanding how to use weight (or BMI) based selection of Noise Index for automated tube current modulation. Don’t forget to check out the easy stuff – like patient centering, use of bismuth shields, and limiting Z axis. Realize that even your contrast injection protocols – volume, rate, blending – might benefit from a weight based approach. Decide how to implement iterative reconstruction, varied by body region.

With these steps you are set to embark on a continual journey. Get started… today!

The Truth about CT Exposure: 1980 to 2012

recent article published in CA: A Cancer Journal for Clinicians states that education of referring physicians, more assertive radiologists, and an increased use of healthcare IT are the keys to reducing patient exposure to radiation.

While these assertions may be true, the article also touched on rising radiation exposure due, primarily, to CT scans. Since the early 1980s, the estimated per capita dose from medical radiation in the US has increased significantly. But this isn’t the whole story…

While it is true that medical radiation from CT has increased markedly since 1980, so has the benefit to health from CT. We no longer do “exploratory surgery” for example, in order to sort out complex diagnostic imaging challenges. The false negative rate from Appendix surgery has plummeted. And cancer diagnosis rates overall are declining while cancer cure rates have gone up substantially, particularly in the last 5 years.

Meanwhile, the radiation dose per CT scan has gone down dramatically as the principles of low-dose CT continue to be better understood and implemented. Scans that used to require 25 mSv of radiation are now being done for 20% of that amount. While negative effects from low dose radiation have never bee proven (below 50 mSv), we still strive to keep our doses as low as possible.

So the issue is not radiation cost, but cost/benefit ratio. Driving a car is dangerous too, but we accept the cost/benefit ration. For CT that ratio is much better!

UW and the ACR Dose Registry

The American College of Radiology’s (ACR) Dose Index Registry pilot project has already amassed a number of studies, according to a presentation given at RSNA 2011. The program strives to accurately track CT radiation dose in order to establish national benchmarks, allowing practices to monitor radiation dose exposure and compare patterns. Although only launched in June 2011, the Dose Index Registry is already up and running and any medical imaging facility can now register for the program.

The University of Washington was the second institution to sign up for the ACR Dose Index Registry. Using a DoseWatch product, we will get real time information on every CT scan and every patient scanned, including the dose each machine puts out in general, and dosage each patient is exposed to per scan and over time. This information then gets forwarded to the central registry maintained by the ACR for monitoring and for comparison purposes.

This should be a very powerful monitoring program and a big boost to safety. We are glad to take part in the program and look forward to the insights that being part of the Dose Index Registry can provide!

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.