limiting the risks

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Limiting the risks of radiationexposure in diagnostic imagingPreston Ray,a Thinh Vu, MD,b Minerva Romero, MD, MPH,a and Nancy D. Perrier, MD, FACS,a

Houston, TX

From the Departments of Surgical Oncologya and Neuroradiology,b The University of Texas M.D. AndersonCancer Center, Houston, TX

THIS REPORT BY THE JOHNS HOPKINS’ GROUP discussesthe development that multiphase computed to-mography (CT) as becoming a favored imagingmodality for complex parathyroid localization.1

The article cites delineation of hyperfunctioningparathyroid tissue from other structures by relatingdensity on unenhanced CT to the rapidity ofenhancement following contrast injection. The‘‘fourth dimension’’ (4D) of perfusion over timehas excellent predictive power for localization.The additional ‘‘washout phase’’ has been citedto increase reader confidence. In this article, Nour-eldine et al recommend eliminating $1 aspects ofserial scans to decrease the effective radiationdosing. We support decreasing radiation exposureto the patient using an informative and respon-sible risk–benefit strategy.

To understand the risk, a basic knowledge ofradiation dosage terms is needed. Effective dose is aprobabilistic estimate of the total amount of radia-tion absorbed at different doses by the tissuesexposed (Table I).2 Measured in Sieverts (Sv)and used mainly to evaluate radiation risks in pa-tients, effective doses are difficult to calculatebecause they depend largely on estimating ab-sorbed doses from CT.2 Although estimating effec-tive dose has many limitations, such as not beingspecific to patient size or gender, it is commonlyused for medical imaging examinations involvingradiation. Exposure is the ionization produced ina specific volume of air as radiation waves stripelectrons from air molecules.2 Absorbed dose is

/j.surg.2014.08.002

d for publication August 22, 2014.

requests: Nancy D. Perrier, MD, FACS, The University of.D. Anderson Cancer Center, 1400 Pressler Dr., Unitouston, TX 77030. E-mail: NPerrier@mdanderson.org.

2014;156:1297-9.

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Elsevier Inc. All rights reserved.

x.doi.org/10.1016/j.surg.2014.08.085

the amount of energy absorbed per unit of massin a particular tissue, measured in grays (Gy).2

Although the radiation used in diagnostic im-aging accounts for <50% of all radiation exposurein the United States,3 a 2004 study suggested thatmedical exposure might be responsible forapproximately 1% of the cancer in the UnitedStates.4 However, it is difficult to isolate radiation-induced cancers (1/1,000 per 10-mSv effectivedose) that are superimposed on the normal back-ground risk for other cancers (approximately40% of the population will be diagnosed as havingcancer at some point in their lives).5 Table II liststhe approximate effective doses for various formsof radiation exposure. Some form of radiation,including radioactive materials and ultravioletrays, is believed to play a role in #10% of all casesof invasive cancer.6

A 2009 study brought medical radiation expo-sure risks into the spotlight. In 2007, an estimated72 million CTs were performed in the UnitedStates---nearly 200,000 CT per day, or >2 scans persecond.4 Essentially, the issue of radiation expo-sure narrows down to 2 overarching questions:How can risk be minimized, and how much istoo much exposure? With awareness, clinicianscan make informed decisions about this risk–benefit ratio pertaining to diagnostic imaginginvolving radiation.7 Avoiding low-quality imagingreduces the need for repetitive scanning. Accord-ing to the principle of ALARA (as low as reason-ably achievable), the absorbed dose should bethe lowest needed for a good image.8 The ImageGently and Image Wisely campaigns representmany professional organizations working to reducethe use of medical radiation in children andadults, respectively. Predicting radiation risk for in-dividual patients is difficult because the risk de-pends on the patient’s size, gender, age, andtargeted organs. The risk is greater for young pa-tients than for older patients because young pa-tients have longer to live with the absorbed doseand their tissues are more sensitive to radiation

SURGERY 1297

Table I. Typical effective radiation doses fromcommon diagnostic imaging examinations13

ExaminationTypical effectivedose (mSv)

Range(5th–95thpercentile)

95th/5thpercentileratio

Ultrasound 0.0 — —X-ray

Skull 0.03 0.012–0.06 5.0Chest 0.02 0.008–0.037 4.6Abdomen 0.7 0.26–1.4 5.4Pelvis 0.7 0.3–1.3 4.3

CTHead 2.0 0.9–3.0 3.3Chest 8.0 2.4–16.0 6.7Abdomen 10.0 4.0–18.0 4.5Pelvis 10.0 4.0–18.0 4.5

Table II. Levels of radiation for various types ofexposure from diagnostic imaging examinations13

Exposure

Approximateeffective

dose (mSv)Radiationequivalent

Ultrasonography 0.0 —Working as an

international flightattendant for 1 y(600 flights)

4 2 head CT scans

Natural backgroundradiation (1 y)

2.4 120 chest x-rays

Chest x-ray 0.02 3 internationalflights

CTHead 2.0 100 chest x-raysChest 8.0 4 head CT scansAbdomen 10.0 4.2 y of natural

backgroundradiation

4DCT (4-stage) 27.0 >8 y of naturalbackgroundradiation

CT, Computed tomography.

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damage. In addition, the sensitivity of the targetedorgan has a significant impact on the effectivedose, depending on the concentration of mito-chondria and the frequency of mitosis. The riskcan be greater for females than for males if breasttissue is exposed to radiation. Because of thesevariations in risk, specific protocols cannot bedeveloped, and treating clinicians must treat eachpatient according to the patient’s needs.

Four-dimensional CT (4DCT) for imaging hyper-functional parathyroid glands represents a good

example of the need to carefully assess the balancebetween risks and benefits. The dose absorbed bythe parathyroid is 57.5 times higher (92 vs 1.6 mGy)on average with 4DCT than with sestamibi scan-ning.9 Therefore, 4DCTmust be used with caution.9

However, a conservatively estimated absorbed doseof 27mSv received in a 4-stage 4DCTexamination in-creases a patient’s annual cancer risk by only0.019%.10 Given the very small risk, this particularscenario has a favorable risk–benefit ratio.10

Reducing the 4DCT examination from 4 stages to3 would diminish the effective dose to approxi-mately 21 mSv without lowering the examination’saccuracy.11 Reducing the examination to 2 stages,however, would drastically lower the likelihood ofaccurately localizing the abnormality.11,12 Overall,the potential benefits of quality 4DCT scanning tolocalize a parathyroiddisease canoutweigh the risks.

The safety of each patient ultimately rests ontheir clinician’s educated assessment of those risks.Clinicians should ensure that all diagnostic imag-ing examinations are of high quality and need notbe repeated. As endocrine surgeons, we can helpour referring physicians by encouraging them toallow us to order scans based on quality andnecessity of ‘‘roadmapping’’ the case, not fordiagnostic purposes. We can help our patients bybeing knowledgeable about radiation risks so thatwe can effectively inform a patient with sporadicprimary hyperparathyroidism that the risks ofperforming a good, quality, diagnostic 4DCT ex-amination are minimal compared with the benefitsof localizing an adenoma. The importance ofaccurate localization to help facilitate cure andeliminate future studies can ensure that diagnosticimaging procedures do not needlessly compromisepatient safety.

REFERENCES

1. Noureldine SI, Aygun N, Walden MJ, Hassoon A, Gujar SK,Tufano RP. Multiphase computed tomography for localiza-tion of parathyroid disease in patients with primary hyper-parathyroidism: How many phases do we really need?Surgery 2014;156:1300-7.

2. McNitt-Gray MF. AAPM/RSNA physics tutorial for residents:topics in CT. Radiation dose in CT. Radiographics 2002;22:1541-53.

3. National Council on Radiation Protection & Measurements.Report no. 160: ionizing radiation exposure of the popula-tion of the United States. Bethesda: National Council onRadiation Protection & Measurements; 2009.

4. Berrington de Gonz�alez A, Mahesh M, Kim KP, BhargavanM, Lewis R, Mettler F, et al. Projected cancer risks fromcomputed tomographic scans performed in the UnitedStates in 2007. Arch Intern Med 2009;169:2071-7.

5. Amis ES Jr, Butler PF, Applegate KE, Birnbaum SB, Brate-man LF, Hevezi JM, et al. American College of Radiology.

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American College of Radiology white paper on radiationdose in medicine. J Am Coll Radiol 2007;4:272-84.

6. Anand P, Kunnumakkara AB, Sundaram C, Harikumar KB,Tharakan ST, Lai OS, et al. Cancer is a preventable diseasethat requires major lifestyle changes. Pharm Res 2008;25:2097-116.

7. Redberg RF. Cancer risks and radiation exposure fromcomputed tomographic scans: how can we be sure thatthe benefits outweigh the risks? Arch Intern Med 2009;169:2049-50.

8. Brateman L. Radiation safety considerations for diagnosticradiology personnel. Radiographics 1999;19:1037-55.

9. Mahajan A, Starker LF, Ghita M, Udelsman R, Brink JA,Carling T. Parathyroid four-dimensional computed tomog-raphy: evaluation of radiation dose exposure during preop-erative localization of parathyroid tumors in primaryhyperparathyroidism. World J Surg 2012;36:1335-9.

10. Hunter GJ, Schellingerhout D, Vu TH, Perrier ND,HambergLM. Accuracy of four-dimensional CT for the localization of

abnormal parathyroid glands in patients with primary hyper-parathyroidism. Radiology 2012;264:789-95.

11. Kelly HR, Hamberg LM, Hunter GJ. 4D-CT for preoperativelocalization of abnormal parathyroid glands in patients withhyperparathyroidism: accuracy and ability to stratify pa-tients by unilateral versus bilateral disease in surgery-naiveand re-exploration patients. AJNR Am J Neuroradiol 2014;35:176-81.

12. Hunter GJ, Ginat DT, Kelly HR, Halpern EF, Hamberg LM.Discriminating parathyroid adenoma from local mimics byusing inherent tissue attenuation and vascular informationobtained with four-dimensional CT: formulation of amultinomial logistic regression model. Radiology 2014;270:168-75.

13. Wall BF, Hart D. Revised radiation doses for typical X-rayexaminations. Report on a recent review of doses to patientsfrom medical x-ray examinations in the UK by NRPB.National Radiological Protection Board. Br J Radiol 1997;70:437-9.