As this article demonstrates, iterative reconstruction is a very powerful way to reduce dose without impacting diagnostic ability. Key points of the authors include, “To reduce patient and operator radiation dose involves optimization of medical imaging equipment and best control of the equipment by the operator. … The results of our study confirm in a large patient number reflecting the routine clinical setting that the image noise reduction technology allows a significant reduction in radiation dose. … The substantially lower radiation dosage achieved in a routine clinical setting with the image noise reduction technique, provide further evidence of the substantial impact of the new technology. They indicate potential reduction in radiation dosage in invasive and interventional cardiology with more diffusion of newer radiation technology in clinical practice.”
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.
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.
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.
This interesting paper talks about the use of iterative reconstruction to help lower the radiation dose of screening CT colonography.
Of course, as with all screening exams, the first order of priorities is to do no harm – hence the motivation to keep the radiation dose especially low.
The challenge is to lower dose without compromising diagnostic power.
For about the past two years, here at UW Medicine (Seattle) we have been using Model Based Iterative Reconstruction (VEO, GE Healthcare) for all our CT colonography exams. As recommended in this article, we also keep the kVp low – 80 or 100, which also helps to reduce the dose.
The result is a very low dose exam, but with excellent image quality and low image noise. This helps to make great coronal/sagittal reconstructions plus very nice 3D fly-through on the post-processing workstation.
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.
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.
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.
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.
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.
At the 2014 ISCT-sponsored MDCT meeting in San Francisco – dose reduction was a key theme during all four days.
Iterative reconstruction was a common theme of an overall dose reduction program. While adaptive statistical iterative reconstruction (ASIR) now has been well-shown to reduce average doses by up to 40% without impact on image quality, the hot topic was model-based iterative reconstruction (MBIR) in its various forms.
Consensus is now developing around MBIR being capable of 50-70% dose reductions incremental to adaptive statistical iterations. While image appearance may be somewhat different from that of filtered back projection, it is now pretty clear that such different appearance does not compromise diagnostic power. Indeed, with experience, some radiologists have developed a preference for the image appearance of MBIR.
“Don’t Skip the CTA” that’s the word going out to patients with advanced renal failure based on findings of researchers in Baltimore. In a study presented at June’s International Society for Computed Tomography (ISCT), Dr. Barry Daly demonstrated how CTA using moderate doses of IV contrast negatively affects only a small percentage of patients and provides valuable information that outweighs the chance of adverse effects.
However, because lower dose is better for patients, especially that small portion at risk with normal doses, Daly and his team also did a study of low-kVp, low-contrast-dose CTA in chronic renal failure patients. This technique is possible due to the advances in CT technology that have allowed radiologists the ability to get more out of smaller amounts of iodine.
While the low kVp techniques enabled much lower doses of iodinated contrast and resulted in images that looked great, the dual-energy CT technique may have accomplished this effect even better!
With dual-energy, you get the best of both worlds. You get the benefit of lower kVp effect (kEv in GE units), plus the ability to look at images which are equivalent to 100 or 120 kVp from the same CT raw data. Essentially, you still achieve substantial iodine dose reduction, but also get very dense HU enhancements in vessels and organs.
The bottom line is this: CTA isn’t something that patients with advanced renal failure should think about skipping. There is a too big a risk for going into surgery without one. The key is finding the safest technique to reduce the dosage level of iodinated contrast while getting the best images. Dual-energy CT may be the best solution out there.
Another major organization has joined the U.S. National Cancer Institute to support CT lung cancer screening as a life saving procedure! Recently, the American Lung Association updated its recommendations to support low-dose CT lung screening for smokers and former smokers.
Lung cancer continues to be the leading cause of death in the U.S., with more than 150,000 deaths annually and a five year survival rate as low as 15 percent. However, research from the US National Cancer Institute’s Lung Cancer Screening Trial gives promising hope. The study found that low-dose CT can reduce mortality rates by at least 20 percent among smokers and former smokers. Other published reports have estimated even higher rates of mortality gains! According to the LCST, individuals between the ages of 55 and 74 years who are current or former smokers of at least 30 pack-years and have no history of lung cancer are ideal candidates for lung cancer screening with CT.
Currently, besides never smoking, low-dose CT screening is the only viable option for significantly reducing the risk of lung cancer. The ALA’s recommendation of this medical imaging exam is an important step toward the development of widespread population-based CT screening program through the U.S.
The ALA joins the National Comprehensive Cancer Network, the first major professional organization to recommend low-dose lung cancer screening last fall.
For more information on factors that may effect the widespread implementation of lung cancer screening, see this post on low-cost screening.
Is low-cost an added benefit to widespread lung cancer screening? According to this article, from April’s Health Affairs—yes! The study on this much debated about topic asserts that routine CT lung cancer screening of high-risk individuals would save thousands of lives annually for less than one dollar a month per patient, if implemented throughout the US. According to these figures, the cost of low-dose lung cancer screening could be less than that for both breast cancer screening and colorectal cancer screening.
As we’ve pointed out, lung cancer screening is effective and life saving. For high- risk patients, those who are multiple pack year smokers for 25 years or more, screening provides significant benefits. For these individuals, low-dose CT screening reduces the number of lung cancer deaths by 20 percent!
Despite this, widespread lung cancer screening has yet to be implemented nationwide, largely due to cost. This study reports interesting and encouraging data about widespread implementation of the procedure, though. However, we must remember that there are also reputable articles which report much higher cost numbers when adjusted for quality-life-years saved. It is necessary to take these studies into account, too.
Looks like the jury may still be out on this one!
According to a new study based on the International Early Lung Cancer Action Program (I-ELCAP), lung cancers identified in low-dose CT screening programs are similar to those identified by non- screening means. The research results, which were released on March 27 in Radiology, further alleviate concerns that cancers detected through low- dose CT screening are less aggressive than those found through other means, and therefore demand less attention and resources. In fact, the frequency of small-cell carcinoma and adenocarcinoma were similar for cancers detected through screening programs and outside the screening setting.
This study is another brick in the wall of evidence building for the value of low radiation dose CT lung cancer screening in high risk asymptomatic smokers. Regardless of whether nodules are solid or “ground glass” (non-solid), growth occurs that is similar in the screened populations and in those detected of having lung cancer due to symptoms.
While it is true we do not yet have a data-based analysis of costs versus quality life years saved, the evidence that screening is worthwhile continues to become stronger. “The CT scanners we have now are really phenomenal,” with resolution that continues to improve as the radiation dose falls, “so that the amount of information you can get out of them for emphysema, for coronary artery risks, and so on, continues to increase,” says Dr. Claudia Henschke, lead author of this study.
She goes on to point out that cancers detected via low dose CT screening “are real cancers that would kill you if they weren’t discovered early, so it kind of underscores again the data that we had shown in ELCAP and that NLST (National Lung Screening Trial) has shown — that screening for lung cancer saves lives.” And that is the key takeaway.
As the war on cancer continues, a group of U.S. oncologists picked its “Top Five” most essential advances in cancer care, as reported by HealthDay news. I’m pleased to announce that CT-based lung cancer screening is listed as one of the major advances for 2011.
The report, published in the Journal of Clinical Oncology, placed only targeted drug therapy above CT-based lung cancer screening. Both advancements will be major game changers for cancer care. The report confirms that the U.S. National Cancer Institute found that screening smokers and former smokers with a CT chest scan was “dramatically better than the chest X-ray.”
There now is no question about this! In high risk heavy smoker populations, low dose CT- lung cancer screening saves lives… and quite a few. The challenge now is getting our healthcare delivery systems to incorporate this approach into routine preventative medical practices….but only for high risk individuals. We need to make these scans easy to obtain, fast to perform, very low in radiation, covered in health plans, and inexpensive.
The good news is that all of these things are possible. Turning CT-lung cancer screening into a regular practice for in-need individuals is very do-able!
Recently, the National Comprehensive Cancer Network has come forward in favor of lung cancer screening with low-dose CT. The NCCN is the first professional organization to perform the comprehensive review and update their recommendations to promote lung cancer screening.
This update further validates the key concept that high risk patients benefit from screening. High risk patients for lung cancer diagnoses are those who are multiple pack year smokers for 25 of more years. For these individuals, low- dose CT screening reduces the number of lung cancer deaths by 20 percent.
While we don’t really know the full cost of a screening program – such as the costs of working up false positive CT findings, the benefit in lives saved seems to justify considering screening now.
Fortunately, the CT technique for screening is low dose and involves low radiation dosage.
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!