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.

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.

Should cumulative radiation dose be tracked?

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

In a recent article published online1, the authors state in their introduction that radiation dose risk is cumulative and an increasing number of patients are undergoing multiple follow-up procedures at regular intervals. Is cumulative dose of concern in patients who have repeated scans? The jury is still out on this question. There is support for tracking cumulative dose2 as well as thought that cumulative dose should not be given any importance when making decisions about individual patients3, 4.

Radiation risk is based on the linear no-threshold model which states that all radiation exposure carries some risk but these need to be weighed against the benefits of the radiation exposure. This linear relationship implies that irrespective of which CT scan a patient is receiving, the absolute risk is the same. There is no increase in sensitivity from the increasing dose received from repeated CT scans, only an accumulation of probability. The linear no-threshold model would break down and not make any sense if there was an increase in sensitivity from repeated scans.

Consider the analogy of driving to work every day which has a risk of a fatal automobile accident associated with it. We do not keep track of the number of times we have driven in the past and its influence on whether we drive tomorrow or not. Similarly, as far as medical decisions are concerned, cumulative dose should not play a factor in deciding if a CT scan should be ordered or not. The benefit of getting the CT may far outweigh the risks. Also, individual risks are hard to quantify as all our risk models are based on large population data.

It is very important that we do not misuse the patient history information about previous scans to influence our medical decision today. Educating the physicians and the public on this is paramount to avoid such misuse.


  1. Roobottom CA and Loader R. Virtual Special Issue Radiation dose reduction in CT: dose optimisation gains both increasing importance and complexity! Clinical Radiology, 2016; 71(5): 438–441.
  2. Sodickson A, Baeyens PF, Andriole KP, et al. Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults. Radiology 2009; 251: 175-84.
  3. Durrand DJ, Dixon RL, Morin RL. Utilization Strategies for Cumulative Dose Estimates: A Review and Rational Assessment. Journal of the American College or Radiology 2012; 9: 480-485.
  4. Eisenberg JD, Benjamin Harvey HD, Moore DA et al. Falling Prey to the Sunk Cost Bias: A Potential Harm of Patient Radiation Dose Histories. Radiology: 2012; 263(3): 626-628.

Gentle and wise use of CT radiation dose

This comprehensive article demonstrates the importance of CT dose monitoring and utilizing strategies to achieve ALARA (as low as reasonably achievable) doses while maintaining image quality for optimal clinical diagnosis. The authors also describe how the use of technology can improve the radiation dose efficiency of CT scanners.

Radiation Dose Management in CT: Is it easy to accomplish?

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

At the AHRA conference in Las Vegas recently, Dr. Pizzutiello, a medical physicist, discussed the complexity of CT radiation management and monitoring in diagnostic imaging. With the growing use of CT exams being performed and radiation dose in CT being a hot topic in the radiology community, it is imperative to monitor radiation dose from the CT exams as well as observe trends over time. Regulations now require that CT dose has to be documented and available on demand, CT protocols be revisited on an annual basis and incidents with high dose CT exams be reviewed. Several states around the US have CT regulations or are in the process of regulation implementation. It is a monumental task to monitor and manage dose, especially for large hospitals.

There are several dose management software products available that can help in managing the dose. Dose management is, however, a team effort and it is not possible to do this effectively without a team of radiologists, technologists, and medical physicists participating in this important task.

At our institution, we have been managing dose using a commercial product, Dose Watch (General Electric Healthcare) and also have a radiation safety committee within the department to review dose trends and make intelligent decisions based on our dose data. We have also been participating in the ACR CT Dose Index Registry since its inception and review our trends and benchmark values to our peer institutions. This is definitely a good idea if one is unaware of dose trends at their institution and how it compares to others around the nation.

Dose monitoring is complex but a necessary patient safety tool and, if well planned, can be accomplished and maintained with the help of dedicated professionals who understand the importance of the task.

The importance of dose alerts

At UW Medicine, we use a dose alert system built into DoseWatch (GE Healthcare) as well as in the individual CT scanners. While this is a good safety mechanism to prevent accidents and notice high dose exams, it’s not the whole answer. As this article points out, “… in practice, CT technique and therefore patient dose depends very much on patient size.”

Size specific dose exposure (SSDE) is a better measure which we will be hearing more about in the near future.


Low dose techniques for urinary stone detection

This article highlights that it is possible to achieve much lower radiation dose CT scans for commonly employed types of CT studies – the CT for urinary tract stones is one of the most common.

While not done everywhere, attention to detail can produce remarkable reductions in patient radiation without compromising diagnostic power.

Use of a lower kVp will actually make stones a bit brighter.

Careful attention to patient centering in the gantry can make a difference of up to 40% in dose.

And the use of iterative reconstruction techniques is now widely accepted to not compromise detection, yet with marked dose reduction – whether it be statistical iterative reconstruction, model based iterative reconstruction, or some blend of the two.

Radiologists and technologists both need to understand the importance of these tricks and the physics behind each.

Optimizing Radiation Dose

Standardizing dose description parameters and metrics is an ongoing and very active area in ACR and nationwide. This will be a big help to comparing metrics between institutions and over time. The SSDE (Size Specific Dose Estimate) is a good step in that direction.

But this article also points out the large impact of exam appropriateness on dose. It is an impressive fact that a profound way to lower population dose is to avoid doing inappropriate exams. Tools such as the ACR Appropriateness Criteria or Computerized Decision Support at the point of order entry can empower appropriateness review. And every radiologist needs to increase their awareness of exam appropriateness in daily work.

Striving towards ALARA

This direction of combining a higher noise index (NI) to get lower dose images and then correcting for the resultant noise by using an increased percent of iterative reconstruction (ASIR) is exactly the way to go when striving towards “as low as reasonably achievable” (ALARA) – in my opinion.

At UWMC, we have for a couple of years now gone even further – we use NI in the 30-36 range and routine 70 percent ASIR as a standard for all our CT imaging except high resolution lung (which is NI 25 and ASIR 30%). According to the ACR CT Dose Registry, we are in the bottom 10% of their data base for CT dose….. but the images are very good.

Check out this article to learn more.

Despite Initial Challenges, ACR Dose Index Registry is a Success!

The American College of Radiology’s (ACR) CT Dose Index Registry (DIR) program was introduced in May 2011. The DIR is a data registry that allows institutions across the United States to send their anonymized CT exam dose information to the ACR to be saved in a database at ACR. Institutions are then provided with semi-annual feedback reports comparing their results by body part and exam type to aggregate results for adult and pediatric exams. Facilities can then compare their CT dose indices to regional and national values.

At UW, we enrolled in the DIR in May 2011 and since then have been sending encrypted DICOM structured dose report files from all of our CT scanners to ACR. Doing so required collaboration between ACR, IT, PACS personnel and the on-site physicist. Implementation involved several challenges, including software installation and data transmission consistency problems. Since numerous institutions are involved, the ACR required an exam mapping process via the Radlex Playbook to unify the protocol classification. This mapping process has been the most challenging factor in the implementation process. These challenges have been overcome and data is being successfully transmitted to and analyzed by the ACR.

The first report comparing adult patient dose data (CTDI and DLP by medical examination and by scan) between our site and others around the region and country was made available in January 2012 and the second one in September 2012.  For each exam, the report includes box-plots and histogram data for a variety of standard protocols.  The second report estimated the size specific dose estimate from the scout for each patient exam.

The ACR CT Dose Index Registry program has been very successful and is a useful tool for dose data mining and will eventually establish national benchmarks for CT dose indices.

For more information on the Registry, please see this article here!

A Radiologist Replies to ‘Medical Radiation Soars, With Risks Often Overlooked’

A few weeks ago, the New York Times featured an article, “Medical Radiation Soars, With Risks Often Overlooked.” The article brought up some valid points about radiation, but also requires readers to take a step back when processing some of the information given.

Yes, as the article ascertains, radiation has its indisputable medical advantages, in addition to its potential medical downsides. The amount of medical imaging, including CT scans, has significantly increased over the last few decades, as more life-saving procedures are discovered and as technology develops. As a result, some patients are subjected to higher levels of radiation, which, according to this article, is “believed to account or 1.5 percent of cancers” in the United States.

The piece goes on to say that “the cancer-causing effects of radiation are cumulative” and that doctors and hospitals fail to track the amount of radiation patients have already been exposed to when ordering a new exam. While it is critical to practice “As Low As Reasonably Achievable” (ALARA) for every protocol and to closely scrutinize every exam request for appropriateness, there is absolutely no evidence that risk from well spaced CT exams is cumulative. Therefore, canceling an otherwise appropriate exam because of cumulative dose may not be in the patient’s best interests. For all CT exams a risk/benefit evaluation should be made by a well informed radiologist. For the existence of multiple prior exams alone to change the risk/ benefit ratio would be extremely rare.

Additionally, the claim that “no one” keeps track of how much radiation patients have been exposed to is inaccurate. A number of institutions, including UW, are a part of the American College of Radiology’s Dose Index Registry, a program striving to accurately track CT radiation dose in order to establish benchmarks, monitor patient radiation dose exposure, and compare patterns. More recently, a pediatric dose registry was introduced to perform similar functions, but for a younger demographic.

Both doctors and patients should be as informed as possible when it comes to radiation. Understanding the risk/ benefit ratio is an important part of this—and no appropriate medical imaging exam should be cancelled if it will benefit the patient, especially if its radiation level is ALARA.

First Look: Pediatric Dose Registry

Pediatric radiation dosage continues to be a hot topic in the news. Just recently, a new team of researchers stepped out with a goal of reducing overall radiation exposure level for pediatric patients. The team, called the Quality Improvement Registry in CT Scans in Children (QuIRCC), is made up of researchers from six children’s hospitals and is currently in the process of researching and developing the first pediatric CT dose index registry.

The QuIRCC comes after a May 9 mandate from the U.S .Food and Drug Administration (FDA) requiring manufacturers to design scanners with young patients in mind, intended to reduce overall radiation exposure levels in pediatric patients.  However, the QuIRCC project is about more than just manufacturing. In fact, the project is designed to help “child-size” scanning protocols by offering accurate metrics to measure radiation exposure in children.

The development of such a registry for children, alone, is especially important. But the other important feature here in this project is establishing the target ranges of dose per exam type that are considered acceptable. This should lower or damp down the large range of variance in dose for similar exam types between nearby medical centers.

Here at UW we know the importance of dose registry programs, as we got involved in the American College of Radiology Dose Index Registry pilot project right away.  This new dose index registry will make great strides for ensuring safe radiation practices for patients of all ages.