Radiation dose tracking might sound esoteric,but it is increasingly important to everyone involved inimaging – including patients. Dr. Mahadevappa Mahesh, Professorof Radiology, Cardiology and Chief physicist at Johns Hopkins Hospitalin Baltimore, USA, says: “Dose tracking helps us ensure that the dosesof ionising radiation delivered to patients when they have X-rays, CT scans, fl uoroscopy and nuclear medicine are within specified ranges. “It is growing in importance around the world as the use of radiation-basedimaging increases.” Click to read more: FutureofImagingCampaign2018-DoseTracking
Authors: Pamela T. Johnson, MD and Elliot K. Fishman, MD
The pillars of excellence in body CT are guided by traditional goals of quality (protocol optimization and interpretative accuracy) and safety (radiation modulation and avoiding contrast-induced nephropathy). As medicine transitions to high-value practice, excellence has evolved into providing the most diagnostically accurate information possible from each CT examination while protecting patients from unnecessary scans, radiation, and costs. Body CT is a leading source of patient radiation exposure in medical imaging [1, 2], and the Image Wisely Campaign encourages all radiology professionals to safeguard patients by pledging to optimize radiation use [3. In body CT, radiation dose is tempered by limiting the number of phases performed during each CT and modulating tube current and peak kilovoltage [4, 5]. The ACR recently released their second slate of Choosing Wisely recommendations, which advises radiologists to avoid abdominal CT protocols with noncontrast and delayed phases unless the additional acquisitions provide an incremental increase in valuable diagnostic information [6.
Reduction of CT dose can compromise image quality and confound diagnosis by increasing noise, which has been addressed by manufacturers developing iterative reconstruction. Radiologists may not be aware of additional resources available at the scanner and the workstation to increase lesion conspicuity and detection as image quality and quantity decrease, including virtual noncontrast data sets from dual-energy CT, 3-D rendering (maximum intensity projection [MIP], volume rendering [VR], and cinematic rendering [CR]), computer-assisted diagnosis, and texture analysis. [Read more….]
Received 23 December 2014, Revised 22 March 2015, Accepted 23 April 2015, Available online 12 May 2015.
With ongoing technological developments in radiation protection, CT has become integral to pediatric radiology, and has established itself as an important part of the diagnostic algorithm [1–6]. Nevertheless, the awareness of the possible effects of ionizing radiation in the young and growing bodies of children requires that radiation dose and scan protocols be adapted to size, age, and clinical needs [6–9], according to the ALARA (as low as reasonably achievable) principles. In addition to stringent justification requirements, continuous optimization is imperative. Well-established radiation dose reduction methods are available for every modern CT scanner, such as automatic tube current modulation [10–12] and tube potential optimization [12,13]. In addition, correct patient positioning in the scanner isocenter [12–14], individually adjusted scan boundaries, the choice of an anterior–posterior or posterior–anterior supine projection, and appropriate reduction of the Scan Projection Radiograph (SPR) dose [12,15], must be considered. Another very important issue is avoiding multiple scan series in pediatric CT whenever possible. If necessary, clinically unstable and non-cooperative children should be sedated to reduce movement artifacts and prevent repeated scans . One of the most powerful optimization tools is to compare the doses delivered to Diagnostic Reference Levels (DRLs), which are also now becoming available for pediatric CT [16–20]. In most cases, DRLs represent the 3rd quartile of doses from dose surveys, indicating a level of dose below which 75% of all institutions operate. However, especially in pediatric CT, these dose levels have been lowered quite a bit recently, indicating that there is still some more potential for optimization. Nevertheless, these values cannot be thought of as representing the optimum values. Rather, they are values which, when continuously exceeded, should trigger a process to determine the reasons these unusually high doses were used and an attempt should be made to lower them. To estimate doses to children from CT Dose Index (CTDI) readings, the concept of the Size Specific Dose Estimate (SSDE)  helps to visualize the relation of pediatric doses to doses delivered to adults, since, due to their reduced body diameter, the same CTDI values result in considerably higher organ and tissue doses in children.
Last but not least, radiation staff education is one of the most efficient ways to enforce scientific “good practice” in radiological institutes and to reduce the radiation dose to patients [22–25].
The purpose of our study was to evaluate the efficacy of staff training and continuous education on the radiation doses applied in pediatric CT scans.
2. Materials and methods
Pediatric CT scans were performed in the emergency department (Somatom Sensation Cardiac 64; Siemens Medical, Erlangen, Germany), the divisions of musculoskelatal radiology (Brilliance 64, Philips, The Netherlands), traumatology (Somatom Sensation Open, Siemens, Germany), neuroradiology (Somatom Sensation 4 until September 2010, Somatom Sensation 64 thereafter, both Siemens, Germany), and surgery (Somatom Definition Flash, Siemens, Germany). On the emergency and the surgical scanner, pediatric radiologists were in charge, and radiologists with pediatric radiology experience were present in the divisions of musculoskeletal radiology, neuroradiology, and traumatology. The technical staff consisted of licensed radiographers. On all scanners, quality control programs were performed, including regular (semi-annual) CTDI calibration and monthly image quality tests.
To avoid image quality loss below diagnostic requirements, the radiologists were made aware of the on-going optimisation and asked to report image quality issues immediately.
2.1. Data acquisition
Examination data from all pediatric and adolescent patients under 18 years of age, who underwent standard cranial, thoracic, abdomen–pelvis, and thoracic–abdomen–pelvis (trunk) scans between 2010 and 2012, were extracted retrospectively from the PACS system (IMPAX DS 3000, Agfa Healthcare, Mortsel, Belgium). Extracted dosimetric data included dose length product (DLP) values for each series obtained from the Dicom Structured Reports.
Standard ranges were defined as follows:
cranial scan (CCT): apex to skull base
thoracic scan: seventh cervical (or first thoracic vertebra) to sinus phrenicocostalis
abdomen–pelvis scan: diaphragmatic dome to symphysis
trunk scan: seventh cervical (or first thoracic vertebral) to symphysis.
All data were checked and excluded if the examination range indicated a non-standard range due to the patients’ individual indication, such as, e.g., a combined neck and thorax CT, a thorax including upper abdomen scan, or an abdomen–pelvis scan including the femora. CT examinations in which the dose report was not recorded in the PACS system were also excluded. Data evaluation was performed per series. If examinations consisted of more than one series (e.g., scans with and without contrast for oncological cases), every single series was treated as a separate scan.
2.2. Staff training
Staff training consisted of yearly obligatory radiation protection briefings, as stipulated by legislation, combined with continuing education elements. These sessions were organized as 90-min presentations, including a discussion part. During these training sessions, dosimetry concepts and optimization measures, including DRLs, were presented, together with new relevant publications and studies, as well as radiation protection rules for personnel and patients. Topics and presenters changed every year.
In 2010, the main topic was the newly published national DRLs (NDRLs) for pediatric examinations, including CT, since an amendment to the national medical radiation protection bylaw, which included pediatric DRLs for the first time, had been issued . The presentation was offered three times in December 2010 to reach all radiologists and radiology technologists.
2.3. Data analysis
To extract longitudinal trends, data were evaluated and compared statistically for 2010 (i.e., before training dedicated to pediatric CT), 2011, and 2012. In order to be able to compare changes in dose applied as a result of optimization for the different examination types and age ranges in question, the percentages of examinations that exceeded the age- and procedure-specific DRLs were calculated. For this comparison, dose data from infants below one month of age were pooled in a group and compared to the DRL for newborns. Data from children between one and twelve months of age were compared to the DRLs for one-year-olds, from thirteen months to five years to five-year-olds, and so on, according to the usual instructions applied when comparing childrens’ exposures to DRLs using age banding and benchmarking against the upper limit of the appropriate age band. Since DRLs are different in most countries, the most comprehensive and complete European values from Germany, Austria, and Switzerland were used (Table 1). However, no reference levels were available for trunk scans. To still be able to make a valid comparison, the respective DLPs for chest and abdomen–pelvis scans were added and reduced by 20% to account for the overlap in the scan range. Twenty-percent has been shown to be an appropriate reduction for these combined scans in adults . Dose optimization as a result of staff training was anticipated to result in a decrease in the relative number of patient scans that exceeded the appropriate DRLs.
|Cranial CT||Thorax CT||Abdomen–Pelvis CT||Trunk CT|
Comparison values derived from thorax and abdomen/pelvis DRLs. AUT, GER, CH corresponds to Austrian, German, and Swiss values.
Statistical computations were performed using SPSS version 21.0 (IBM, New York, USA). In order to assess the association between age and DLP, linear and non-linear regression analyses were performed. Due to the intrinsically skewed nature of dose data, the DLP was described using median as well as 1st and 3rd quartiles. The percentages of scans with DLPs above diagnostic reference levels were determined. Data from the traumatology department were evaluated separately since trauma CT scan protocols differed from the protocols applied by the other departments due to diagnostic requirements.
Optimization, including retrospective anonymized evaluation of patient doses, and comparison of average doses applied with DRLs, is a legal requirement in Austria. Nevertheless, ethics board approval was obtained beforehand.
The authors have nothing to disclose and confirm that there are no conflicts of interest associated with this publication.
Examination numbers were 1799 in 2010, 1582 in 2011, and 1525 in 2012. Dose reports were not included into the PACS for 79 series in 2010, 53 in 2011, and 31 in 2012. Another 477 series were excluded in 2010 because of a non-standard scan range; 407 in 2011; and 449 in 2012. Thus, in total, the rejection rate was 27.3% (1496 scan series). Table 1 shows how cases were distributed between the departments’ scanners.
No image quality issues were reported by staff (radiographers and radiologists) during optimisation.
DLP values exhibited the best correlation with age using an exponential model (R2 from 0.52 for CCT, 0.61 and 0.63 for abdomen–pelvis and thoracic scans, respectively, and 0.71 for trunk scans) and the least correlation when a linear model was applied (R2 from 0.34 to 4.49), with a quadratic model only fitting minusculely better than the linear model. Therefore, a linear correlation of log(DLP) with age was utilized to determine whether statistically significant dose reductions were achieved.
Table 3 summarizes the ANCOVA results that assessed whether the effects of dose reduction were statistically significant. Patient doses were significantly reduced for CCT both from 2010 to 2011, and 2012 with respect to 2011. The same was true for thoracic scans. For abdomen–pelvis scans, a reduction in the DLPs was significant for 2011 with respect to 2010. Average DLP values were also reduced slightly in the following year, but significance could not be demonstrated. For trunk scans, a slight reduction in average DLPs occurred; however, it was not significant (p > 0.05). This can also be seen in Fig. 1a–d, showing the box plots for the data. Case numbers (see also Table 2) for abdomen–pelvis, and, especially trunk scans, were quite low. Fig. 1a–d also clearly demonstrates a reduction in the range of variation within the age bands, seen from the widths of the boxes (1st to 3rd quartile) and the whiskers (10th to 90th percentile).
|Department||Cranial CT||Thorax CT||Abdomen–Pelvis CT||Trunk CT|
|Neuroradiology (old scanner)||589|
|Neuroradiology (new scanner)||202||684||707||–||1||–||–||2||2||–||2||–|
Another measure designed to quantify optimization outcome is the number of scans that exceed the reference levels, as shown in Table 4. For all examinations, the relative number of these scans was reduced. Compared to the German reference levels, for example, there was a reduction of over 40% to approximately 6% in CCT scans, and from approximately 9% and 26% (abdomen–pelvis and trunk scans, respectively) to zero.
|% Exceeding German DRL||% Exceeding Austrian DRLs||% Exceeding Swiss DRLs|
|Traumatic cranial CT||76||88||83||50||50||37||68||68||75|
|Traumatic trunk CT||43||52||20||n/a||n/a||n/a||53||57||20|
3.1. Trauma CT scans
An analysis of dose data was performed only for CCT and trunk scans, since examination numbers were too low for the other examinations.
No dose reduction was seen in traumatic CCT scans (Table 4), and the number of scans performed that exceeded DRLs increased from 76% in 2010 to 88% in 2011 and 83% in 2012, if the German values are used as a reference. For trunk scans, a reduction by a factor of two was observed, starting with 43% (compared to the German values) in 2010 to 20% in 2012. However, since the sample size in 2012 contained only 15 scans, and included no scans for children up to five years of age, this reduction cannot be considered credible.
The application of Dose Reference Levels, in combination with staff education and awareness, has been demonstrated to be effective in dose optimization in pediatric computed tomography. The presentation of NDRL for pediatric cranial and body computed tomography to our already well-trained radiology technologists and radiologists enabled a radiation dose reduction for most pediatric CT examinations. This effect was also shown to be sustainable. This corresponds nicely to a rather recent publication indicating that one reason for unusually high doses in pediatric radiology was that radiation dose levels were never determined, and thus, not known .
Paolicchi et al. demonstrated the role of radiological staff training for adult chest, abdomen–pelvis, and whole body CT scans , indicating that training of radiologists and technologists is a key issue in optimizing CT protocols, and thus, can significantly reduce radiation dose . They published also a radiation dose reduction while preserving diagnostic image quality in pediatric head CT examinations, after a radiologic staff training . Schindera et al. reported the same effect for adult paranasal sinuses, brain, chest, pulmonary arteries, and abdomen CTs . The authors reported that the largest decrease in radiation dose was reached for paranasal sinus and pulmonary arteries scans. No significant dose reduction for abdominal CTs was found; suboptimal image quality for low-contrast lesions in abdominal CTs was most likely identified as the reason. Education and training programs for radiological institutes was concluded to be effective in achieving substantial reduction in CT dose . Sheyn et al. reported that staff radiation safety education can improve radiation safety practices in pediatric interventional radiology, and thus, decrease exposure to radiation for both staff and patients . Georges et al. demonstrated in 2009 that training in radiation protection for interventional cardiologists, and the use of simple and cost-free dose-reduction techniques, were associated with a 50% reduction in radiation exposure to patients undergoing invasive cardiac procedures, without any loss of diagnostic information .
This work extends the scope of these studies, demonstrating the effects of continuing education and training on pediatric CT, and endorses the efficacy of the concept of DRLs. These two concepts complemented each other very well. We observed a significant decrease in DLP for all of our pediatric CT scans, including cranial, thoracic, abdomen–pelvis, and trunk CTs, during the observation interval from 2011 and 2012, compared to 2010, with the only exception being trauma CT scans. However, the DRLs are not directly applicable to trauma CT scans because of their specific requirements. This is most obvious in head scans, where the DRLs correspond to brain scans rather than the bony skull. Nevertheless, future work should be invested in imaging criteria including appropriate dose levels for trauma scans with special emphasis on pediatric examinations.
The relative number of scans performed at a dose exceeding the appropriate reference level was assessed. However, it must be noted that DRLs can only be applied on average doses and cannot be used on an individual basis. Therefore, it is inappropriate and misleading to argue that individual doses (DLPs in this case) that exceeded the DRLs indicated that too high a dose was used. If the values constantly exceeded that for standard patients and examinations, the dose level applied would be graded as “unusually high”, triggering the need to research the reasons for this higher level. Therefore, this type of assessment does not comply with the basic idea of reference Levels. However, if an unusual or rather high number of scans exceed the DRLs, and the rate decreases during optimization without any image quality issues arising, it seems reasonable to declare the education effort a success. Normally, doses quite below the appropriate DRLs can be applied since the actual values are not optimal values [28,29], but merely represent values below which 75% of institutions operate. However, care should be taken to ensure that patients and diagnostic requirements are comparable. In this work, DRLs from other countries were used, since a European consensus on values has not yet been reached, and Austrian levels do not cover all the indications we assessed in this work.
4.1. Limitations of this study
The scanner in the neuroradiology department has been replaced during this study (from a 4- to a 64-slice scanner) in September 2010. Most of the CCT scans in the study originated from this department. The protocols previously implemented at the four slice scanner were optimized before the scanner exchange, and transferred with only slight adjustments due to the new technology to the new machine. Scan protocols were individually adjusted to the patients’ physique at both, the old and the new machine. However, it cannot be ruled out completely, that the scanner change had an effect on the dose reduction, but this effect should have been minor. Another limitation was the low case number of trunk scans, due to which no statistically significant dose reduction in terms of DLP could be demonstrated. However, the effect can be seen in the reduction of the relative share of scans with doses greater than the DRLs (from approximately one quarter to zero). Last but not least, since the doses from traumatic scans did not change, future work should be dedicated to the definition of image quality requirements and optimization of these protocols.
Modern CT scanners provide numerous possibilities for optimizing radiation dose and applying it more efficiently, like automatic tube current modulation, individual kVp optimization, and iterative reconstruction, to name a few . However, continuous education of personnel to ensure that they are familiar with these possibilities, in order to utilize the potential for dose reduction, must be emphasized.
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There’s been a lot in the media lately about radiation exposure from medical imaging, and many of my patients are asking about it. They want to know if radiation from mammograms, bone density tests, computed tomography (CT) scans, and so forth will increase their risk of developing cancer. For most women, there’s very little risk from routine x-ray imaging such as mammography or dental x-rays. But many experts are concerned about an explosion in the use of higher radiation–dose tests, such as CT and nuclear imaging.
In 2006, about 62 million CT scans were performed in the United States, compared with just three million in 1980. There are good reasons for this trend. CT scanning and nuclear imaging have revolutionized diagnosis and treatment, almost eliminating the need for once-common exploratory surgeries and many other invasive and potentially risky procedures. The benefits of these tests, when they’re appropriate, far outweigh any radiation-associated cancer risks, and the risk from a single CT scan or nuclear imaging test is quite small. However, in light of the 20-fold increase in the use of these tests, experts wonder if we are courting future public health problems.
Some of this worry was fueled by the April 2010 release of the President’s Cancer Panel report, “Reducing Environmental Cancer Risk: What We Can Do Now.” Among other concerns, the report highlighted the rise in radiation exposure from medical imaging. The panel outlined ways to minimize radiation exposure from medical sources and recommended that clinicians keep a running tally of the amount of radiation their patients receive from medical imaging.
Exposure to ionizing radiation on the rise
The radiation you get from x-ray, CT, and nuclear imaging is ionizing radiation — high-energy wavelengths or particles that penetrate tissue to reveal the body’s internal organs and structures. Ionizing radiation can damage DNA, and although your cells repair most of the damage, they sometimes do the job imperfectly, leaving small areas of “misrepair.” The result is DNA mutations that may contribute to cancer years down the road.
We’re exposed to small doses of ionizing radiation from natural sources all the time — in particular, cosmic radiation, mainly from the sun, and radon, a radioactive gas that comes from the natural breakdown of uranium in soil, rock, water, and building materials. How much of this so-called background radiation you are exposed to depends on many factors, including altitude and home ventilation. But the average is 3 millisieverts (mSv) per year. (A millisievert is a measure of radiation exposure; see “Measuring radiation.”)
Exposure to ionizing radiation from natural or background sources hasn’t changed since about 1980, but Americans’ total per capita radiation exposure has nearly doubled, and experts believe the main reason is increased use of medical imaging. The proportion of total radiation exposure that comes from medical sources has grown from 15% in the early 1980s to 50% today. CT alone accounts for 24% of all radiation exposure in the United States, according to a report issued in March 2009 by the National Council on Radiation Protection and Measurements.
If you mention the measurement of radiation, many people will recall the classic Geiger counter with its crescendo of clicks. But Geiger counters detect only the intensity of radioactive emissions. Measuring their impact on human tissues and health is more difficult. That’s where the sievert (Sv) and millisievert (mSv) come in. These units, the ones most commonly used in comparing imaging procedures, take into account the biological effect of radiation, which varies with the type of radiation and the vulnerability of the affected body tissue. Taking these into account, millisieverts describe what’s called the “equivalent dose.”
Ionizing radiation and cancer risk
We’ve long known that children and teens who receive high doses of radiation to treat lymphoma or other cancers are more likely to develop additional cancers later in life. But we have no clinical trials to guide our thinking about cancer risk from medical radiation in healthy adults. Most of what we know about the risks of ionizing radiation comes from long-term studies of people who survived the 1945 atomic bomb blasts at Hiroshima and Nagasaki. These studies show a slightly but significantly increased risk of cancer in those exposed to the blasts, including a group of 25,000 Hiroshima survivors who received less than 50 mSv of radiation — an amount you might get from two or three CT scans. (See “Imaging procedures and their approximate effective radiation doses.”)
The atomic blast isn’t a perfect model for exposure to medical radiation, because the bomb released its radiation all at once, while the doses from medical imaging are smaller and spread over time. Still, most experts believe that can be almost as harmful as getting an equivalent dose all at once.
Imaging procedures and their approximate effective radiation doses*
|Procedure||Average effective dose (mSv)||Range reported in the literature (mSv)|
|Bone density test+||0.001||0.00–0.035|
|X-ray, arm or leg||0.001||0.0002–0.1|
|X-ray, panoramic dental||0.01||0.007–0.09|
|X-ray, lumbar spine||1.5||0.5–1.8|
|CT, cardiac for calcium scoring||3||1.0–12|
|Nuclear imaging, bone scan||6.3|
|CT, whole body||variable||20 or more|
|Nuclear imaging, cardiac stress test||40.7|
|*The actual radiation exposure depends on many things, including the device itself, the duration of the scan, your size, and the sensitivity of the tissue being targeted.
+Dual energy x-ray absorptiometry, or DXA.
|Source: Mettler FA, et al. “Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog,” Radiology (July 2008), Vol. 248, pp. 254–63.|
Higher radiation–dose imaging
Most of the increased exposure in the United States is due to CT scanning and nuclear imaging, which require larger radiation doses than traditional x-rays. A chest x-ray, for example, delivers 0.1 mSv, while a chest CT delivers 7 mSv (see the table) — 70 times as much. And that’s not counting the very common follow-up CT scans.
In a 2009 study from Brigham and Women’s Hospital in Boston, researchers estimated the potential risk of cancer from CT scans in 31,462 patients over 22 years. For the group as a whole, the increase in risk was slight — 0.7% above the overall lifetime risk of cancer in the United States, which is 42%. But for patients who had multiple CT scans, the increase in risk was higher, ranging from 2.7% to 12%. (In this group, 33% had received more than five CT scans; 5%, more than 22 scans; and 1%, more than 38.)
What to do
Unless you were exposed to high doses of radiation during cancer treatment in youth, any increase in your risk for cancer due to medical radiation appears to be slight. But we don’t really know for sure, since the effects of radiation damage typically take many years to appear, and the increase in high-dose imaging has occurred only since 1980.
So until we know more, you will want to keep your exposure to medical radiation as low as possible. You can do that in several ways, including these:
Discuss any high-dose diagnostic imaging with your clinician. If you need a CT or nuclear scan to treat or diagnose a medical condition, the benefits usually outweigh the risks. Still, if your clinician has ordered a CT, it’s reasonable to ask what difference the result will make in how your condition is managed; for example, will it save you an invasive procedure?
Keep track of your radiation exposure. The President’s Panel recommended that imaging device makers indicate the radiation dose for each x-ray, and that clinicians record radiation exposures in patients’ medical records. The FDA is considering both ideas. In the meantime, you can keep track of your own x-ray history. It won’t be completely accurate because different machines deliver different amounts of radiation, and because the dose you absorb depends on your size, your weight, and the part of the body targeted by the x-ray. But you and your clinician will get a ballpark estimate of your exposure.
Consider a lower-dose radiation test. If your clinician recommends a CT or nuclear medicine scan, ask if another technique would work, such as a lower-dose x-ray or a test that uses no radiation, such as ultrasound (which uses high-frequency sound waves) or MRI (which relies on magnetic energy). Neither ultrasound nor MRI appears to harm DNA or increase cancer risk.
Consider less-frequent testing. If you’re getting regular CT scans for a chronic condition, ask your clinician if it’s possible to increase the time between scans. And if you feel the CT scans aren’t helping, discuss whether you might take a different approach, such as lower-dose imaging or observation without imaging.
Don’t seek out scans. Don’t ask for a CT scan just because you want to feel assured that you’ve had a “thorough checkup.” CT scans rarely produce important findings in people without relevant symptoms. And there’s a chance the scan will find something incidental, spurring additional CT scans or x-rays that add to your radiation exposure.
Celeste Robb-Nicholson, M.D.
Dr. Aaron Sodickson helped in the preparation of this article. Dr. Sodickson is a diagnostic radiologist at Brigham and Women’s Hospital in Boston.
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