Clinical Gastroenterology and Hepatology
Volume 8, Issue 3 , Pages 231-232, March 2010

Personalized Dose Reduction for Computed Tomography Scanning: Size Matters, so Does Prior Radiation Exposures

  • Mannudeep K. Kalra, MD, DNB

      Affiliations

    • Massachusetts General Hospital Imaging, Massachusetts General Hospital, Boston, Massachusetts
    • ,
  • Isaac R. Francis, MD

      Affiliations

    • Department of Radiology, University of Michigan Hospitals, Ann Arbor, Michigan

published online 14 December 2009.

Article Outline

 

The article, “Acute Pancreatitis: Computed Tomography Utilization and Radiation Exposure Are Related to Severity but Not Patient Age” by Morgan et al1 is timely and a valuable addition to the existing literature written on the subject of radiation dose in patients undergoing repetitive computed tomography (CT) scans. We agree with the points made by the authors and several other investigators who recently have written and commented on the subject of excessive radiation dose caused by imaging and its reduction. In this clinical setting, the referring physicians, gastroenterologists, surgeons, and radiologists should work together as a team to eliminate unnecessary routine CT scanning and utilize ultrasound or magnetic resonance imaging (MRI) if the needed information can be obtained with these nonionizing imaging modalities. However, if the desired information can be obtained only with CT, dose reduction techniques should be used that effectively reduce radiation dose to the patient without sacrificing diagnostic information.

In this original research article, investigators from the University of Alabama at Birmingham present some interesting data on radiation exposure and utilization of CT scanning for evaluation of a benign but serious disease entity of acute pancreatitis.1 Morgan et al1 report that the number of CT examinations per person and therefore the associated radiation doses were related to the severity of the acute pancreatitis and its complications and unfortunately not to the age of the patients. The fact that subjects with less severe episodes of acute pancreatitis received a lower radiation dose from fewer abdominal CT examinations or perhaps no CT imaging at all actually provides some information on appropriateness of CT ordering practice. On the other hand, the authors raise a serious but not surprising issue of a lack of awareness of the concept of cumulative radiation exposure, particularly to young patients, and absence of strategies to tailor CT radiation dose according to patient age.

Deterministic adverse effects such as skin burns, hair loss, and cataracts, which typically require acute radiation exposure of at least 1000 mGy, are unlikely to result from CT scanning performed for most clinical indications. However, stochastic carcinogenic effects occur at much lower dose levels, and repeat CT scanning increases cumulative exposure, which raises the probability of radiation-induced cancer. In that sense, younger patients receiving a higher cumulative radiation dose from CT scanning have a longer life expectancy after radiation exposure and therefore are at higher risk of radiation-induced carcinogenesis.2, 3

As shown by Morgan et al1 in their study on CT scanning in patients with acute pancreatitis, repetitive CT scanning can deliver a substantial cumulative radiation dose to patients. Prior publications also have documented substantial cumulative radiation doses with repetitive CT scanning in patients with nonmalignant conditions, such as urinary tract calculi, cystic fibrosis, and inflammatory bowel diseases.4, 5, 6 Katz et al4 reported that 4% of their subjects with nephrolithiasis underwent 3 or more abdominal-pelvic CT scans between 1996 and 2002 at a single institution, which were associated with estimated effective doses of 20 to 154 mSv.3

Another recent study documented the prevalence of repetitive CT scanning in patients with Crohn's disease associated with a mean cumulative effective dose of up to 36 mSv and greater than 76 mSv in about 15% of patients.6

A more disconcerting report came from an analysis of patients with cystic fibrosis undergoing CT scanning, in which Donadieu et al5 found cumulative lifetime effective doses of 2 to 76 mSv and a decrease in the age at first CT examination from 20 years for patients born before 1980 to about 2 years for patients born after 1997.

All these studies point to increasing use of CT scanning in modern medical practice and underscore the importance of personalization of CT scanning protocols to clinical indications and patient age.4, 5, 6 Sadly, none of these studies opine on reasons for “ignoring” or “failing to address” the need for dose personalization in patients who are likely to undergo repetitive scanning in this era of heightened concern and awareness about the potential for radiation-induced carcinogenesis. Hypothetically, it is not difficult to imagine that radiologists and physicists have been outpaced by the blistering pace of change in CT technology in the past 10 years on almost an annual basis and an increasing number of radiologic procedures that need to be interpreted in a rapid but accurate manner to maintain a smooth workflow and patient care.

There are, however, clear opportunities for change on the horizon. Recent studies on dose reduction have become focused on specific clinical indications that are benign and/or often require follow-up CT imaging.2 Several investigators have reported that a lower radiation dose can provide diagnostic information in clinical indications such as appendicitis, kidney stones, and cystic fibrosis.7, 8, 9, 10, 11 The use of composite scanning parameters that simultaneously account for patient size, clinical indications, and number of prior CT examinations also recently has been described in a large single-institution study.12 Finally, CT manufacturers also have realized that it is just not enough to display the prettiest pictures; consequently, they have developed numerous scanner hardware and software techniques to reduce the radiation dose while maintaining a reasonable image quality, such as automatic exposure control, image processing algorithms, dose-efficient collimators and filters, and iterative reconstruction techniques.2, 13, 14

Morgan et al1 list as a limitation of their study that effective radiation doses for patients undergoing CT scanning for acute pancreatitis were estimated based on published standards, and they therefore may have underestimated or overestimated actual radiation doses. Extrapolation of estimated effective doses from other sources as described by the authors likely is inaccurate because prior studies have reported that there is a 4- to 8-fold variability in radiation doses between different institutions for similar CT examinations.15 This is compounded further by the fact that the current CT radiation dose metrics do not suggest actual patient dose but provide a broad estimate of approximate radiation dose. As a result, little has been done to date to address the issue of archiving or recording organ-absorbed radiation dose from the CT scanners to estimate individual cumulative effective doses.

The onus for radiation dose optimization for patients with acute pancreatitis undergoing 1 or more CT examinations lies with both the referring physicians as well as the radiologists. Clearly, CT is the imaging modality of choice for the evaluation of patients with acute pancreatitis because of the level of information that it provides and how the information impacts clinical management of patients. These benefits need to be clearly understood and accounted for before decisions can be weighed against the potential long-term, small incremental increase in radiation-induced cancer with CT scanning. To maximize the benefits, we believe that ordering physicians should make sure that recommendations such as weekly CT examinations for evaluation of some patients with acute pancreatitis are applied appropriately. On the other hand, it is the duty of the radiologist to ensure that CT protocols address the need to minimize the risks of radiation dose associated with repetitive scanning without undermining the ability to make important observations and diagnoses. To initiate corrective steps it is therefore important for the radiologists and ordering physicians to work closely. Until an electronic flagging system can be initiated to automatically flag the radiologist about repetitive CT scanning, ordering physicians should convey this information to the radiologists and in turn radiologists also proactively should seek out this information. At the Massachusetts General Hospital, the radiology information systems partly address this issue by alerting the ordering physician as well as the protocoling radiologist about the presence of prior imaging tests in similar body regions. It is anticipated that in the future vendors also will make these tools available on their systems. This is particularly important for young patients. Specific protocols must reduce the radiation dose for younger patients and those undergoing repetitive CT scanning for an age-specific or number of prior CT examinations. These protocols, whether or not specific to the repetitive CT imaging, should tailor the radiation dose to the weight or body mass index of the patient, use automatic exposure control techniques available on most modern CT scanners, and restrict acquisition of multiple series of CT images unless absolutely necessary. Another important aspect of dose reduction at our institution is the emphasis on focused CT scanning limited to the body region of interest from a clinical perspective, particularly for additional sets of CT images. Also, routine acquisition of precontrast or noncontrast images must be limited if postcontrast images are to be acquired. An important alternative imaging technique for acute pancreatitis in young patients or those undergoing repetitive CT scanning is MRI, which can provide required diagnostic and prognostic information with equal or greater accuracy.16, 17 MRI, however, may not be a viable option in unstable or acutely ill patients who cannot lie still in the MRI, as has been correctly pointed out by Morgan et al.1

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References 

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 Conflicts of interest The authors disclose no conflicts.

PII: S1542-3565(09)01229-4

doi:10.1016/j.cgh.2009.12.001

Clinical Gastroenterology and Hepatology
Volume 8, Issue 3 , Pages 231-232, March 2010