- Email: [email protected]
Radiation Protection in the Era of Helical CT: Practical Patient Based Programs for Decreasing Patient Exposure
Radiation Protection in the Era of Helical CT: Practical Patient Based Programs for Decreasing Patient Exposure Steven Birnbaum, MD Practical methods are described in this review for the practicing radiologist to minimize radiation dose to patients particularly with reference to multidetector helical computed tomography. Technical, educational, and management methods are outlined in detail as well as their rationale. Preliminary results of this comprehensive program are also outlined after the first year of its institution. Semin Ultrasound CT MRI 31:46-52 © 2010 Elsevier Inc. All rights reserved.
I
n February 2004, as a radiation safety officer (RSO) at the Southern New Hampshire Medical Center, I became aware of the imaging history of a then 14-year-old male with hypercalciuria who had a history of renal stone disease. The computed tomography (CT) technologists presented me with 5 X-ray folders as we were not yet on a Picture Archiving and Communications System (PACS). In reviewing his previous studies, I realized he had 14 helical renal stone CT studies. When I consulted our health physicist for dosimetry calculations, similar to what I had done many times in the past with pregnant patients who had inadvertent radiation exposure during gestation, I was horrified at the results, particularly as the patient at that time weighted 240 lbs. The physicist suggested genetic counseling at a tertiary care medical center. After discussion with the patient’s urologist, I became the patient’s personal radiologist, such that additional CT studies would not be performed unless radiologic consultation occurred. Since 2004, he has had no CT studies, 12 renal ultrasounds, 12 abdominal films, and 1 one-shot intravenous pyelogram, with obvious tremendous decrease in radiation exposure during that interval. This experience became the paradigm upon which I based my subsequent radiation safety programs. Fast forward 6 months. My 22-year-old daughter was struck by a car when jogging. She suffered a skull fracture, severe concussion, pelvic fractures, and a severe knee injury. When transferred to a trauma center, she underwent CT from
Department of Radiology, Southern New Hampshire Medical Center, Nashua, NH. Department of Radiology, Parkland Medical Center, Derry, NH. Address reprint requests to Steven Birnbaum, MD, 8 E Pearl St, Nashua, NH 03060. E-mail: [email protected]
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0887-2171/10/$-see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1053/j.sult.2009.09.006
head to pelvis, appropriately given the severity of her injuries. The results were reassuring to me, telling me that she would recover with minimal sequelae, which she has. On day 2 post injury, when still in the intensive care units, she had a blood count drawn from the arm where her IV ran, demonstrating a diminished hematocrit. Rather than redraw blood from her contralateral arm, she was sent to radiology for a repeat abdomen and pelvis CT study. Her study showed a small amount of free fluid in the cul-de-sac of the pelvis. The pelvic CT was repeated to further fill the bladder with contrast and delineate the free fluid. The radiologists then wanted to repeat her entire study several hours later to insure there was no change in the free fluid. I declined their offer at this point. I found the surgical chief resident, whose team had ordered the study, and demanded an explanation. I found an astonishing lack of knowledge and awareness of these issues in this physician as well in the referring physicians with whom I worked.1 The second portion of my program was born; that of education of clinicians, radiologists, patients, administrators, risk managers, and insurance companies as to the potential dangers of unrestrained use of helical CT. This paper will outline those efforts and the practical measures all radiologists and their departments can establish to restrain patient radiation exposure.
Technical Strategies for Decreasing Radiation Exposure From CT Radiation physics, radiation biology, and issues involving radiation induced carcinogenesis will not be discussed in this paper as these topics are well covered in other essays in this
Radiation protection in the era of helical CT volume. In addition, as a general and interventional radiologist who did a CT fellowship, I am not a physicist, but instead a clinician on the front lines of CT use. All radiologists who read CT studies should be familiar with the technical factors involved with radiation protection with their particular scanner.2 All the major manufacturers have instituted radiation reduction algorithms for their scanners. They differ significantly and may affect the efficacy of using breast shields in female patients. The following factors should be used by all radiologists to minimize radiation dose with their particular CT scanners.
Coning to the Body Part Being Scanned In the performance of plain film studies, all radiologists know and have been trained to insure that imaging is coned to the body part being imaged. A radiologist reading a lumbar spine film does not want to observe an abdominal film (KUB) performed for the anterior image. CT is no different. A CT pulmonary arteriogram in a young woman should not include the thyroid gland or any of the upper abdomen that significantly increases radiation dose. An abdominal CT study evaluating the liver should not go half way into the pelvis. All radiologists should be monitoring their studies for this.
Centering of the Patient in the CT Gantry Centering of the patient in the CT gantry optimizes image quality and diminishes radiation dose.3 All CT technologists should be aware of this and radiologists should spot-check their technologists to insure this occurs.
Adjusting Technique to Patient Age and Body Habitus The Image Gently Program has worked diligently to insure that radiologists and technologists lower CT technique to the lowest level possible in pediatric patients to minimize dose. Although CT dose is mainly driven by mAs, but kVp may also be lowered as well to minimize dose.4 Some manufacturers are color coding techniques on their scanners to assist technologists in the choice of technique. Radiologists should, however, continually spot-check the dose length product (DLP) and a derived effective dose from this, to insure their technologists are following these protocols. In our hospitals, we are able to perform regular abdomen/pelvis CT studies in 20 kg children for appendicitis with about 1 millisievert (mSv) of estimated dose.
Automatic Dose Modulation and Noise Index The equipment manufacturers have used various techniques to diminish dose, including automatic dose modulation that is the CT equivalent of photo-timing for plain x-rays.2 One manufacturer (Siemens) does this “real time” as the scanner is obtaining helical data and adjusts the tube output to patient density “on the fly”. In this situation, breast shields are not effective in dose reduction, as the presence of the shields artificially increases perceived density and thus increases the technique. The other 3 major manufacturers use Z axis dose
47 modulation that uses the CT scout images and density readings from those to vary technique on the basis of X-ray attenuation. In these scanners, breast shields may significantly decrease effective dose to the female breast when placed on the patient after the performance of the scout images. If placed on the patient before the performance of the scout images, increased density will be detected and the scanner will automatically increase the technique and the dose. In addition a parameter known as noise index may be adjusted to decrease dose. This parameter will diminish the photon flux through the patient to create a grainier image as it is increased. While images with a high noise index may not be the most pleasing images to view, they are often diagnostic at significantly lower doses and can be easily used in certain clinical situations, such as follow up studies in younger patients with chronic diseases and pediatric patients.
Shielding Bismuth breast shields have been shown to significantly decrease dose to the female breast with 3 of the 4 major manufacturer’s scanners.5,6 In our hospitals, they are used routinely for every female patient. Although the risk of breast irradiation from CT is clearly miniscule in the elderly patient, even with multiple studies, we have found that a uniform policy insures that those patients most at risk will have the shields in place. Thus, we have no age limit on the use of shielding. The shields do cause some metallic streak artifact that is minimal but does seem to effect the visualization of the right coronary artery with cardiac CT, and thus we do not use them in cardiac CT studies. We also do not routinely shield the orbits of infants or use thyroid shields. The thyroid shields do cause significant streak artifact around the mandible on neck CT studies as they are very close to scanning volume of interest and thus we do not use them.
Spot-Check of Effective Dose All modern multislice CT scanners report a DLP value from which an estimated effective dose can be calculated using standard conversion factors. Even though these are dose estimates that are probably inaccurate on an absolute level, they do act as an internal control for a particular scanner and practice such that estimated effective doses can be compared. By doing this, I have found multiple incidences where technologists did not follow our usual protocols and needless elevated dose was administered to patients. When noticed and dealt with in a careful, responsible manner, technologists will not do this with time and further experience.
The Pregnant Patient A not uncommon request is the evaluation of the pregnant patient for pulmonary embolism. In our institutions, we do CT pulmonary arteriograms using breast shields and coning as per our usual protocols. In addition, these patients are administered 2 cups of thin barium used for upper gastrointestinal series about 1 hour before the CT study to provide internal shielding from scatter irradiation to the fetus by the
S. Birnbaum
48 barium in the abdomen. This technique has been shown to significantly reduce scatter radiation dose to the fetus.7
Education The importance of education of radiologists, referring providers, all physicians who use ionizing radiation, and technologists cannot be emphasized enough in the establishment and continuation of a successful, comprehensive patientbased radiation safety program.8 There are no governmental regulations in the United States that govern patient radiation exposure from diagnostic imaging studies. Therefore, it is incumbent upon radiologists, who are the only specialty trained in radiation biology and radiation physics, to educate their colleagues who refer to them as well as those they work with.
Radiologists The mSv is the basic unit of effective radiation dose that is useful in the understanding of medical radiation exposure issues for the practicing diagnostic radiologist. There are 3 types of radiation dose measurement used in radiation protection of patients and workers. These are increasingly commonly expressed in the international units created by the International Commission of Radiation Protection (ICRP). These include the following: 1. Absorbed dose expressed in Gray or milligray (mGy) where 1 mGy equals 100 millirad (previously used non-standard units). 2. Equivalent dose expressed in Sievert or millisievert (mSv) where 1 mSv equals 100 millirem (previously used non-standard units). Dose measurement is extremely difficult in the individual patient and is dependent on many factors, such as the uniformity of the exposure, the type of radiation, and the sensitivity of the tissues exposed. The effective dose is the most important measurement for the practicing radiologist. This entity was developed by the ICRP in the late 1970s and later modified in the 1990s.9 The effective dose uses tissue weighting factors and allows comparison of different types of radiation and diagnostic studies to calculate potential carcinogenic risk. This measurement converts a study with irradiation of a portion of the patient into a whole body uniform equivalent dose. This is a dose estimate and should not be taken as a hard-and-fast number for any given study or patient. Radiologists should be fluent in the dose estimates for the CT studies they interpret. New multidetector CT scanners will produce a dose report that can be included in the archiving of the study and the patient’s record. These reports include several parameters as follows: 1. Computed tomography dose index (CTDI)-CTDI is the dose equivalent for a rectangular profile inside the irradiated slice calculated from a standard anthropomorphic phantom. Weighted CTDI (CTDIw) is a dose equivalent value obtained for an irradiated volume cor-
rected for phantom size and averaged for the phantom body part representation. 2. CTDIvol—this parameter corrects the CTDIw for the pitch of the scanner. 3. DLP-this parameter incorporates the z axis of the helical study into a dose parameter by multiplying CTDIvol by the length of the study in centimeters. Using these parameters, it is possible to calculate a gross dose estimate from any given multidetector computed tomography (MDCT) study using the following conversion factors developed by the ICRP that depend on the scanning mode used9 and are multiplied times the DLP: 1. 2. 3. 4. 5.
Head⫺0.0023 mSv/mGy cm Neck⫺0.0054 mSv/mGy cm Chest⫺0.017 mSv/mGy cm Abdomen⫺0.015 mSv/mGy cm Pelvis⫺0.019 mSv/mGy cm
The estimates obtained from these measurements should be considered gross estimates and may only be accurate with an error rate of ⫾20%-30%.9 While not useful in the actual dose calculation received by any individual patient, these estimates are helpful to the practicing radiologist to monitor the radiation output of their scanner and the technologist parameters set for that scanner and similar patients. Radiologists also need to become familiar with the technical parameters involved in producing the MDCT image to maximize image quality and yet minimize radiation dose. A detailed discussion of this topic is beyond the scope of this review. Yet all radiologists interpreting MDCT should be fluent in the concepts of automatic exposure control, noise index, the use of shielding, coning to the body part of interest, and alternatives to MDCT in certain clinical situations.
Technologists All radiologists, once they have reeducated themselves, should be strongly involved in the education, training, and monitoring of their technical staff. They are where “the rubber meets the road”. In the modern radiology department, the radiologists are often some distance from the CT scanners, reading studies electronically, divorced from the minute to minute, day to day, workings of a busy CT department. Successful radiation protection demands a different approach. The active engagement of the radiologist with the technical staff is key in getting their “buy-in” to any radiation protection program. Radiation safety protocols should be emphasized again and again with the technologists. I have found their commitment to these programs to be overwhelmingly positive, often greater than the commitment of radiologists. Technologists should be encouraged to consult with radiologists and bring to the radiologist’s attention patients who may have had frequent exposure to CT radiation. In addition, the technologist is key in the maintenance of a radiation safety program and their role in this need to be clearly defined. The bottom line is that the CT technologist needs to be empowered in the radiation safety process
Radiation protection in the era of helical CT through further education and as a member of the imaging team.
Referring Providers Referring providers have had not much knowledge of radiation biology, radiation physics, and the issues involved with helical CT scanning.10 Concerted efforts need to be made to change this lead by radiologists. In our hospitals, I have given numerous grand rounds on this topic and have distributed an essay for the medical staff that acts as a sort of Radiation Biology 101 substitute. This combined with frequent discussion on a one-on-one basis between radiologists and clinicians will gradually result in a change of culture where radiation issues are considered in the ordering of imaging tests. This is most important in the clinical conditions where young patients, ie, under the age of 40 years, may have frequent CT studies when not carefully monitored, often with not much clinical utility or outcome improvement. In our hospitals these include the following conditions: (1) nephrolithiasis; (2) Crohn’s disease; (3) chronic abdominal pain; (4) pulmonary embolism; (5) pancreatitis; and (6) diverticulitis. We have found specialist physicians to be increasingly aware of these issues and reasonable as to follow up imaging requests. We have worked hard to educate our clinicians to the alternative imaging modalities that can be used in some of these conditions, such as ultrasound and a KUB in renal stone disease and magnetic resonance (MR) enterography in Crohn’s disease. Emergency room physicians deal with a more difficult clinical setting and challenging patient population where CT scanning has assumed a paramount position in diagnosis, management and disposition of patients. Cultural change is more difficult in this setting particularly given the medicallegal environment. Yet with persistent educational efforts, changes in culture are slowly but surely happening in our hospitals. An ER physician in one of our hospitals when confronted with the fact that a 48 years old alcoholic patient with abdominal pain was now getting his eighth normal abdomen/pelvis CT study in 9 months and that this dose was in the range of extrapolated carcinogenesis, said, “Well, I guess we will observe a lot more cancer cases in 10 to 15 years.” Now he regularly consults with the radiology staff when these issues originates. Our philosophy is that we never say, “No”, but instead encourage discussion and consultation. Over time this has been a successful policy. In addition, emergency medicine is documenting an increased awareness of radiation issues.11
Administrators and Risk Managers Radiologists need to take the lead in the education of the administrative personnel in the institutions in which they work. This, too, is often a slow and painful process but can be extremely rewarding with patience and time. Concerns of lost referrals and revenue are minimal given the utility of CT scanning and its role in the diagnostic armamentarium. More concerning are those young patients with frequent exposure, some of whom have had more than 30 abdomen/pelvis stud-
49 ies under the age of 40 for nephrolithiasis. Luckily, these patients are relatively rare. However, in this situation, carcinogenesis risk is real, and it is not hard to convince the risk managers that something needs to be done. It took about 2 years for our original hospital radiation protection program to wind its way through committees, lawyers, risk managers, and administrators until it was finalized. However frustrating during the process, the time it took to do this made everyone on board in a committed manner.
Handling the Frequently Exposed Patient Radiology departments have been encouraged by the American College of Radiology to “define a surveillance mechanism to identify patients with high cumulative radiation doses due to frequent imaging.1” In the hospitals in which I work, we have set up the following system to accomplish this goal using existing information on radiation safety and biology to establish criteria for at risk patients.8 We use the following criteria that are admittedly somewhat arbitrary but are according to available information and report. a. Patient age: Under the age of 40. This is the age threshold often mentioned as being most at risk and takes into account the increased longevity of our patient population as well as data from the atom bomb survivors. b. Diagnoses: Benign diagnoses. No cancer patients are included in this identification process at this time. Certainly, many young cancer patients on various protocols do receive many follow-up studies particularly positron emission tomography-CT fusion studies that may result in high cumulative exposures but we have elected to focus on patients with benign disease first. c. Study types: Five studies of the neck, chest, abdomen, or abdomen/pelvis that would expose the patient to a dose estimate of about 50 mSv. These are dose estimates, not calculations done by physicists, and we have therefore stayed away from using any sort of precise measurement and prefer to use the number of studies in our thresholds. This is in keeping with the difficulties that physicists have in measuring exact dosages in patients given the huge number of variables involved in this process.9,12 d. CT technologists: Our CT technologists have been empowered in this process to actively research imaging histories in the radiology information system (RIS) and report any suspicious histories to the radiologist on duty at that time and then to the RSO. The imaging history and studies are then reviewed and when the criteria are met, the patient is entered into our database of at risk patients. Once a patient is identified using the above system, the following events take place: a. The patient’s demographics are annotated in the RIS with the annotation of “Radiation safety alert/patient
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Figure 1 Sample requisition of “flagged patient.”
has had more than 5 CT studies/consult with radiologist” similar to contrast allergy. See Figure 1. b. Further studies on these patients are only performed with radiologist consultation to assess for clinical appropriateness, the suitability of nonionizing modalities for evaluation instead of CT, or overwhelming clinical indication. c. A certified letter is sent to the referring clinician and the primary care provider, when there is one, when the patient activates the 5 study threshold. This letter discusses the radiation safety issues and the potential risks of further studies. The practitioner is also informed of the necessity of radiologic consultation when further CT studies are needed. d. Although the patient has more than 10 studies listed
above, they are then placed in a higher risk category. In addition to the measures detailed above, a certified letter is sent to the patient. In the course of our development of this program, we have become aware that many of our patients have received care at multiple institutions where they may have additional radiologic studies. Patients in this category should be informed of these issues in a calm manner, so that they can take charge of their medical care, record their imaging history, and have a say in any future imaging. e. The RSO and our consulting physicist are made available for patient and provider consultation as needed. This program has met with high acceptance by patients, clinicians, and most radiologists. Patients and their parents
Radiation protection in the era of helical CT have thanked me for protecting them. The first patient whom we identified 5 years ago and is now 19 years old, has no subsequent renal stone CT studies, 10 renal ultrasounds, 10 KUB’s, and 1 one-shot intravenous pyelogram with a substantial diminution in radiation dose, no significant changes in the clinical management of his continued episodes of renal colic, and no adverse effect upon his health by limiting his CT studies. His urologist has enthusiastically embraced this program and frequently calls for radiologic consultation. The initial phases of this program have been performed in a tedious prospective manner as the patients have presented to our departments and are identified by the CT technologists or radiologists upon review of their imaging history. We are now picking up patients for our program with a more efficient and thorough method using data mining techniques in our RIS. We have been able to identify many more patients in this manner. We run quarterly reports with this technique and flag patients in our RIS and send letters as needed on that basis.
Monitoring a Patient Focused CT Radiation Safety Program Over the past one year, as our program was established we have monitored the results to assess its efficacy. The CT technologists have logged all cases where a flagged patient in the RIS has had a CT study ordered and the outcome documented after radiologist consultation. Fifty-one patients came to the attention of the CT technologists and radiologists in this program. The results of these encounters are as follows: 1. Eight of 51 studies were canceled. 2. Eight of 51 studies were changed to nonionizing modalities, such as ultrasound or MR imaging. 3. Thirteen of 51 studies were performed at the insistence of the clinician. 4. Twenty-one of 51 studies were performed after consultation between radiologist and clinician and agreement upon study indication. 5. One of 51 studies was performed at the insistence of the patient. Clearly this sort of program can decrease the volume and frequency of studies performed in patients who had multiple CT studies. However, most studies are still performed, often without strong clinical indication at clinician insistence, and without change in patient outcome. The need for further education and guidance is clear. These patients came from the following referral sources: 1. Emergency room providers-27/51 2. Hospitalists-10/51 3. Gastroenterologists-7/51 In the community hospital setting, the great majority of patients are either inpatients or emergency room patients, and this is where the focus of our activities has been. The gastroenterologists in our practice have readily adapted to
51 our recommendations and now frequently order MR imaging enterography rather than CT studies. Recent report points to a massive increase in population radiation dose from outpatient office CT and nuclear medicine procedures that we do not have access to in our systems. In conjunction with our CT radiation safety programs, we also have a vigorous hospital wide radiation safety program that includes the following items: 1. Monitoring of fluoroscopy times for all users of ionizing radiation. 2. Notification of the RSO of all patients receiving greater than 30 minutes of fluoroscopy during interventional procedures including cardiac catheterizations and operating room use, with examination of the patient for deterministic effects within 24-48 hours of exposure. 3. Credentialing of all users of fluoroscopy in radiology, cardiology, and the operating room coincident with hospital privilege recredentialing. 4. Mandatory attendance at radiation safety committee meetings of representatives of all users of radiopharmaceuticals and fluoroscopy in all areas of the hospital including cardiologists, pain management specialists and operating room nurses. 5. Quarterly radiation safety committee meetings with discussion of all the above issues. Through the use of all of these avenues, radiation safety in all areas of our hospitals has become a priority and not just an inconsequential after thought.8
Regional, State, and National Efforts There has been an increasing awareness of radiation issues from diagnostic imaging over the last 5 years as I began my work into this issue. In 2001, the FDA issued its first warning on the potential dangers of CT radiation exposure in children followed by a subsequent warning on the lack of efficacy and potential dangers of whole body screening with CT.12,13 In New Hampshire, the state radiology society was an early forum for my efforts. The reaction to my talks was mixed, although I was somewhat inflammatory in my efforts to draw attention to the issue that I had observed first hand. I have given over 30 talks in the state since 4 years. Over time virtually all the hospitals in New Hampshire have begun programs similar to ours with encouragement of the state society. The New Hampshire Medical Society was similarly supportive and encouraged my efforts. The State of New Hampshire has developed a trauma imaging subcommittee in the Department of Health to address the issues of CT radiation exposure in trauma patients (C. Odell, Concord, New Hampshire, August 2009, personal communication). In New York, the Commissioner of public health has sent a letter to every physician in the state warning of the potential dangers of profligate CT scanning.14 There are no government regulations that limit patient exposure to diagnostic imaging. All regulations are aimed at safe occupational expo-
S. Birnbaum
52 sure and the safe handling of radiopharmaceuticals. Too often, as an RSO, I have spent much time addressing state regulatory issues, such as where the positron emission tomographic patients may use a bathroom or the location of the treadmill in the exercise stress laboratory rather than the epidemic of diagnostic imaging radiation exposure. Although I do not relish government involvement in this issue, at this point, there may be no other alternative to stem this tide. Insurance companies have been involved in radiation safety initiatives over the period. In New Hampshire, Anthem Blue Cross/Blue Shield has used a data mining approach in their precertification process to alert practitioners to the potentially frequently exposed patient. They do not deny the study but instead use their thresholds to inform and educate clinicians. Anthem has also set up an extensive web site for both clinicians and patients to access information that is high quality and nonhysterical on these topics.15 My first inclination upon the initiation of this program was cynicism in that I felt they were trying to decrease use and imaging costs but the percentage of patients that fall into this area is relatively small and the infrastructure costs to anthem far exceed their savings in claims. National Imaging Associates, the largest radiology benefits manager in the United States, uses a similar system to alert clinicians to potential frequent radiation exposure (T. Dehn, Manchester, New Hampshire, personal communication). However, their system, which reports an estimated dose to the patient over time, is fraught with methodological issues in that dose per study is an extremely difficult parameter to measure on any 1 patient, given differences in patient body habitus, age, and scanning parameters. The American College of Radiology has taken an activist position on CT radiation safety. The College convened a Blue Ribbon Panel on this issue in December 2006 and produced a White paper in May 2007.16 This paper contained multiple recommendations for improving radiation safety, and its recommendations are steadily and surely being implemented over time. In addition, the American College of cardiology has also embarked on similar programs and recommendations.
Conclusions Radiation exposure to the United States population has increased dramatically over 15 years with advent of helical CT and expansion of some nuclear medicine procedures. Does irradiation from CT cause cancer? We don’t know. Although a single study in an elderly patient is of virtually no concern, younger patients with benign conditions may be regularly and frequently exposed to CT irradiation, often with not much clinical utility and change in outcome. It is imperative that all radiologists become active in the prevention and man-
agement of this epidemic. This epidemic is akin to global warming. All radiologists should have the political, social, and economic strength to manage this issue, as decisions we do or do not make now may come back to haunt us terribly in 10 to 15 years when radiation induced carcinogenesis returns to our society similar to the early 20th century when the dangers of radiation were not well known.
References 1. Birnbaum S: Helical CT: Too much of a good thing. BMJ 334:1006, 2007 2. McCollough CH, Bruesewitz MR, Kofler JM: CT dose reduction and dose management tools: Overview of available options. Radiographics 26:503-512, 2006 3. Li J, Udayasankar U, Toth TL, et al: Automatic patient centering for MDCT: Effect on radiation dose. AJR Am J of Radiol 188:547-552, 2007 4. Keyzer C, Gevenois PA, Tack D: Dose optimization and reduction in MDCT of the abdomen, in Tack D, Gevenois PA (eds): Radiation Dose From Adult and Pediatric Multidetector Computed Tomography. New York, NY, Berlin Heidelberg Springer-Verlag, 2007 5. Hopper KD, King SH, Lobell ME, et al: The breast: In-plane X-ray protection during diagnostic thoracic CT-shielding with bismuth radioprotective garments. Radiology 205:853-858, 1997 6. Hurwitz LM, Yoshizumi TT, Goodman PC, et al: Radiation dose savings for adult pulmonary embolus 64-MDCT using bismuth breast shields, lower peak kilovoltage and automatic tube current modulation. AJR Am J Roentgenol 192:244-253, 2009 7. Yousefzadeh DK, Ward MB, Reft C: Internal barium shielding to minimize fetal irradiation in spiral chest CT: A phantom simulation experiment. Radiology 239:751-758, 2006 8. Birnbaum S: Radiation safety in the era of helical computed tomography: A patient-based protection program currently in place in two community hospitals in New Hampshire. J Am Coll Radiol 5:714-718, 2008 9. European Commission: European Guidelines on Quality Criteria for Computed Tomography. Office for Official Publications of the European Communities, 2000, pp 70. EUR1626EN 10. Lee CI, Haims AH, Monico EP, et al: Diagnostic CT scans: Assessment of patients, physicians and radiologist awareness of radiation dose and possible risks. Radiology 231:393-398, 2004 11. Winslow JE, Hinshaw JW, Hughes MJ, et al: Quantitative assessment of diagnostic radiation doses in adult blunt trauma patients. Ann Emerg Med 52:93-97, 2008 12. Feigal DW: FDA public health notification: Reducing radiation risk from computed tomography for pediatric and small adult patients. Int J Trauma Nurs 8:1-2, 2002 13. United States Food and Drug Administration, Center for Devices and Radiological Health: “Whole Body Scanning Using Computed Tomography”. Available at: http://www.fda.gov/cdrh/ct. Accessed October 21, 2008 14. Daines R. Commissioner of Public Health for the state of New York, Letter to all Practicing Physicians in New York State, September, 2008 15. Anthem.com. Available at: http://www.anthem.com/wps/portal/ ahpprovider?content_path⫽provider/noapplication/f5/s2/t0/pw_ ad85140.htm&state⫽nh&rootLevel⫽0&label⫽Radiation%20Safety% 20Toolkit. Accessed August 30, 2009 16. Amis ES Jr, Butler PF, Applegate KE, et al: American college of radiology white paper on radiation dose in medicine. J Am Coll Radiol 4:272284, 2007
I
n February 2004, as a radiation safety officer (RSO) at the Southern New Hampshire Medical Center, I became aware of the imaging history of a then 14-year-old male with hypercalciuria who had a history of renal stone disease. The computed tomography (CT) technologists presented me with 5 X-ray folders as we were not yet on a Picture Archiving and Communications System (PACS). In reviewing his previous studies, I realized he had 14 helical renal stone CT studies. When I consulted our health physicist for dosimetry calculations, similar to what I had done many times in the past with pregnant patients who had inadvertent radiation exposure during gestation, I was horrified at the results, particularly as the patient at that time weighted 240 lbs. The physicist suggested genetic counseling at a tertiary care medical center. After discussion with the patient’s urologist, I became the patient’s personal radiologist, such that additional CT studies would not be performed unless radiologic consultation occurred. Since 2004, he has had no CT studies, 12 renal ultrasounds, 12 abdominal films, and 1 one-shot intravenous pyelogram, with obvious tremendous decrease in radiation exposure during that interval. This experience became the paradigm upon which I based my subsequent radiation safety programs. Fast forward 6 months. My 22-year-old daughter was struck by a car when jogging. She suffered a skull fracture, severe concussion, pelvic fractures, and a severe knee injury. When transferred to a trauma center, she underwent CT from
Department of Radiology, Southern New Hampshire Medical Center, Nashua, NH. Department of Radiology, Parkland Medical Center, Derry, NH. Address reprint requests to Steven Birnbaum, MD, 8 E Pearl St, Nashua, NH 03060. E-mail: [email protected]
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0887-2171/10/$-see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1053/j.sult.2009.09.006
head to pelvis, appropriately given the severity of her injuries. The results were reassuring to me, telling me that she would recover with minimal sequelae, which she has. On day 2 post injury, when still in the intensive care units, she had a blood count drawn from the arm where her IV ran, demonstrating a diminished hematocrit. Rather than redraw blood from her contralateral arm, she was sent to radiology for a repeat abdomen and pelvis CT study. Her study showed a small amount of free fluid in the cul-de-sac of the pelvis. The pelvic CT was repeated to further fill the bladder with contrast and delineate the free fluid. The radiologists then wanted to repeat her entire study several hours later to insure there was no change in the free fluid. I declined their offer at this point. I found the surgical chief resident, whose team had ordered the study, and demanded an explanation. I found an astonishing lack of knowledge and awareness of these issues in this physician as well in the referring physicians with whom I worked.1 The second portion of my program was born; that of education of clinicians, radiologists, patients, administrators, risk managers, and insurance companies as to the potential dangers of unrestrained use of helical CT. This paper will outline those efforts and the practical measures all radiologists and their departments can establish to restrain patient radiation exposure.
Technical Strategies for Decreasing Radiation Exposure From CT Radiation physics, radiation biology, and issues involving radiation induced carcinogenesis will not be discussed in this paper as these topics are well covered in other essays in this
Radiation protection in the era of helical CT volume. In addition, as a general and interventional radiologist who did a CT fellowship, I am not a physicist, but instead a clinician on the front lines of CT use. All radiologists who read CT studies should be familiar with the technical factors involved with radiation protection with their particular scanner.2 All the major manufacturers have instituted radiation reduction algorithms for their scanners. They differ significantly and may affect the efficacy of using breast shields in female patients. The following factors should be used by all radiologists to minimize radiation dose with their particular CT scanners.
Coning to the Body Part Being Scanned In the performance of plain film studies, all radiologists know and have been trained to insure that imaging is coned to the body part being imaged. A radiologist reading a lumbar spine film does not want to observe an abdominal film (KUB) performed for the anterior image. CT is no different. A CT pulmonary arteriogram in a young woman should not include the thyroid gland or any of the upper abdomen that significantly increases radiation dose. An abdominal CT study evaluating the liver should not go half way into the pelvis. All radiologists should be monitoring their studies for this.
Centering of the Patient in the CT Gantry Centering of the patient in the CT gantry optimizes image quality and diminishes radiation dose.3 All CT technologists should be aware of this and radiologists should spot-check their technologists to insure this occurs.
Adjusting Technique to Patient Age and Body Habitus The Image Gently Program has worked diligently to insure that radiologists and technologists lower CT technique to the lowest level possible in pediatric patients to minimize dose. Although CT dose is mainly driven by mAs, but kVp may also be lowered as well to minimize dose.4 Some manufacturers are color coding techniques on their scanners to assist technologists in the choice of technique. Radiologists should, however, continually spot-check the dose length product (DLP) and a derived effective dose from this, to insure their technologists are following these protocols. In our hospitals, we are able to perform regular abdomen/pelvis CT studies in 20 kg children for appendicitis with about 1 millisievert (mSv) of estimated dose.
Automatic Dose Modulation and Noise Index The equipment manufacturers have used various techniques to diminish dose, including automatic dose modulation that is the CT equivalent of photo-timing for plain x-rays.2 One manufacturer (Siemens) does this “real time” as the scanner is obtaining helical data and adjusts the tube output to patient density “on the fly”. In this situation, breast shields are not effective in dose reduction, as the presence of the shields artificially increases perceived density and thus increases the technique. The other 3 major manufacturers use Z axis dose
47 modulation that uses the CT scout images and density readings from those to vary technique on the basis of X-ray attenuation. In these scanners, breast shields may significantly decrease effective dose to the female breast when placed on the patient after the performance of the scout images. If placed on the patient before the performance of the scout images, increased density will be detected and the scanner will automatically increase the technique and the dose. In addition a parameter known as noise index may be adjusted to decrease dose. This parameter will diminish the photon flux through the patient to create a grainier image as it is increased. While images with a high noise index may not be the most pleasing images to view, they are often diagnostic at significantly lower doses and can be easily used in certain clinical situations, such as follow up studies in younger patients with chronic diseases and pediatric patients.
Shielding Bismuth breast shields have been shown to significantly decrease dose to the female breast with 3 of the 4 major manufacturer’s scanners.5,6 In our hospitals, they are used routinely for every female patient. Although the risk of breast irradiation from CT is clearly miniscule in the elderly patient, even with multiple studies, we have found that a uniform policy insures that those patients most at risk will have the shields in place. Thus, we have no age limit on the use of shielding. The shields do cause some metallic streak artifact that is minimal but does seem to effect the visualization of the right coronary artery with cardiac CT, and thus we do not use them in cardiac CT studies. We also do not routinely shield the orbits of infants or use thyroid shields. The thyroid shields do cause significant streak artifact around the mandible on neck CT studies as they are very close to scanning volume of interest and thus we do not use them.
Spot-Check of Effective Dose All modern multislice CT scanners report a DLP value from which an estimated effective dose can be calculated using standard conversion factors. Even though these are dose estimates that are probably inaccurate on an absolute level, they do act as an internal control for a particular scanner and practice such that estimated effective doses can be compared. By doing this, I have found multiple incidences where technologists did not follow our usual protocols and needless elevated dose was administered to patients. When noticed and dealt with in a careful, responsible manner, technologists will not do this with time and further experience.
The Pregnant Patient A not uncommon request is the evaluation of the pregnant patient for pulmonary embolism. In our institutions, we do CT pulmonary arteriograms using breast shields and coning as per our usual protocols. In addition, these patients are administered 2 cups of thin barium used for upper gastrointestinal series about 1 hour before the CT study to provide internal shielding from scatter irradiation to the fetus by the
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48 barium in the abdomen. This technique has been shown to significantly reduce scatter radiation dose to the fetus.7
Education The importance of education of radiologists, referring providers, all physicians who use ionizing radiation, and technologists cannot be emphasized enough in the establishment and continuation of a successful, comprehensive patientbased radiation safety program.8 There are no governmental regulations in the United States that govern patient radiation exposure from diagnostic imaging studies. Therefore, it is incumbent upon radiologists, who are the only specialty trained in radiation biology and radiation physics, to educate their colleagues who refer to them as well as those they work with.
Radiologists The mSv is the basic unit of effective radiation dose that is useful in the understanding of medical radiation exposure issues for the practicing diagnostic radiologist. There are 3 types of radiation dose measurement used in radiation protection of patients and workers. These are increasingly commonly expressed in the international units created by the International Commission of Radiation Protection (ICRP). These include the following: 1. Absorbed dose expressed in Gray or milligray (mGy) where 1 mGy equals 100 millirad (previously used non-standard units). 2. Equivalent dose expressed in Sievert or millisievert (mSv) where 1 mSv equals 100 millirem (previously used non-standard units). Dose measurement is extremely difficult in the individual patient and is dependent on many factors, such as the uniformity of the exposure, the type of radiation, and the sensitivity of the tissues exposed. The effective dose is the most important measurement for the practicing radiologist. This entity was developed by the ICRP in the late 1970s and later modified in the 1990s.9 The effective dose uses tissue weighting factors and allows comparison of different types of radiation and diagnostic studies to calculate potential carcinogenic risk. This measurement converts a study with irradiation of a portion of the patient into a whole body uniform equivalent dose. This is a dose estimate and should not be taken as a hard-and-fast number for any given study or patient. Radiologists should be fluent in the dose estimates for the CT studies they interpret. New multidetector CT scanners will produce a dose report that can be included in the archiving of the study and the patient’s record. These reports include several parameters as follows: 1. Computed tomography dose index (CTDI)-CTDI is the dose equivalent for a rectangular profile inside the irradiated slice calculated from a standard anthropomorphic phantom. Weighted CTDI (CTDIw) is a dose equivalent value obtained for an irradiated volume cor-
rected for phantom size and averaged for the phantom body part representation. 2. CTDIvol—this parameter corrects the CTDIw for the pitch of the scanner. 3. DLP-this parameter incorporates the z axis of the helical study into a dose parameter by multiplying CTDIvol by the length of the study in centimeters. Using these parameters, it is possible to calculate a gross dose estimate from any given multidetector computed tomography (MDCT) study using the following conversion factors developed by the ICRP that depend on the scanning mode used9 and are multiplied times the DLP: 1. 2. 3. 4. 5.
Head⫺0.0023 mSv/mGy cm Neck⫺0.0054 mSv/mGy cm Chest⫺0.017 mSv/mGy cm Abdomen⫺0.015 mSv/mGy cm Pelvis⫺0.019 mSv/mGy cm
The estimates obtained from these measurements should be considered gross estimates and may only be accurate with an error rate of ⫾20%-30%.9 While not useful in the actual dose calculation received by any individual patient, these estimates are helpful to the practicing radiologist to monitor the radiation output of their scanner and the technologist parameters set for that scanner and similar patients. Radiologists also need to become familiar with the technical parameters involved in producing the MDCT image to maximize image quality and yet minimize radiation dose. A detailed discussion of this topic is beyond the scope of this review. Yet all radiologists interpreting MDCT should be fluent in the concepts of automatic exposure control, noise index, the use of shielding, coning to the body part of interest, and alternatives to MDCT in certain clinical situations.
Technologists All radiologists, once they have reeducated themselves, should be strongly involved in the education, training, and monitoring of their technical staff. They are where “the rubber meets the road”. In the modern radiology department, the radiologists are often some distance from the CT scanners, reading studies electronically, divorced from the minute to minute, day to day, workings of a busy CT department. Successful radiation protection demands a different approach. The active engagement of the radiologist with the technical staff is key in getting their “buy-in” to any radiation protection program. Radiation safety protocols should be emphasized again and again with the technologists. I have found their commitment to these programs to be overwhelmingly positive, often greater than the commitment of radiologists. Technologists should be encouraged to consult with radiologists and bring to the radiologist’s attention patients who may have had frequent exposure to CT radiation. In addition, the technologist is key in the maintenance of a radiation safety program and their role in this need to be clearly defined. The bottom line is that the CT technologist needs to be empowered in the radiation safety process
Radiation protection in the era of helical CT through further education and as a member of the imaging team.
Referring Providers Referring providers have had not much knowledge of radiation biology, radiation physics, and the issues involved with helical CT scanning.10 Concerted efforts need to be made to change this lead by radiologists. In our hospitals, I have given numerous grand rounds on this topic and have distributed an essay for the medical staff that acts as a sort of Radiation Biology 101 substitute. This combined with frequent discussion on a one-on-one basis between radiologists and clinicians will gradually result in a change of culture where radiation issues are considered in the ordering of imaging tests. This is most important in the clinical conditions where young patients, ie, under the age of 40 years, may have frequent CT studies when not carefully monitored, often with not much clinical utility or outcome improvement. In our hospitals these include the following conditions: (1) nephrolithiasis; (2) Crohn’s disease; (3) chronic abdominal pain; (4) pulmonary embolism; (5) pancreatitis; and (6) diverticulitis. We have found specialist physicians to be increasingly aware of these issues and reasonable as to follow up imaging requests. We have worked hard to educate our clinicians to the alternative imaging modalities that can be used in some of these conditions, such as ultrasound and a KUB in renal stone disease and magnetic resonance (MR) enterography in Crohn’s disease. Emergency room physicians deal with a more difficult clinical setting and challenging patient population where CT scanning has assumed a paramount position in diagnosis, management and disposition of patients. Cultural change is more difficult in this setting particularly given the medicallegal environment. Yet with persistent educational efforts, changes in culture are slowly but surely happening in our hospitals. An ER physician in one of our hospitals when confronted with the fact that a 48 years old alcoholic patient with abdominal pain was now getting his eighth normal abdomen/pelvis CT study in 9 months and that this dose was in the range of extrapolated carcinogenesis, said, “Well, I guess we will observe a lot more cancer cases in 10 to 15 years.” Now he regularly consults with the radiology staff when these issues originates. Our philosophy is that we never say, “No”, but instead encourage discussion and consultation. Over time this has been a successful policy. In addition, emergency medicine is documenting an increased awareness of radiation issues.11
Administrators and Risk Managers Radiologists need to take the lead in the education of the administrative personnel in the institutions in which they work. This, too, is often a slow and painful process but can be extremely rewarding with patience and time. Concerns of lost referrals and revenue are minimal given the utility of CT scanning and its role in the diagnostic armamentarium. More concerning are those young patients with frequent exposure, some of whom have had more than 30 abdomen/pelvis stud-
49 ies under the age of 40 for nephrolithiasis. Luckily, these patients are relatively rare. However, in this situation, carcinogenesis risk is real, and it is not hard to convince the risk managers that something needs to be done. It took about 2 years for our original hospital radiation protection program to wind its way through committees, lawyers, risk managers, and administrators until it was finalized. However frustrating during the process, the time it took to do this made everyone on board in a committed manner.
Handling the Frequently Exposed Patient Radiology departments have been encouraged by the American College of Radiology to “define a surveillance mechanism to identify patients with high cumulative radiation doses due to frequent imaging.1” In the hospitals in which I work, we have set up the following system to accomplish this goal using existing information on radiation safety and biology to establish criteria for at risk patients.8 We use the following criteria that are admittedly somewhat arbitrary but are according to available information and report. a. Patient age: Under the age of 40. This is the age threshold often mentioned as being most at risk and takes into account the increased longevity of our patient population as well as data from the atom bomb survivors. b. Diagnoses: Benign diagnoses. No cancer patients are included in this identification process at this time. Certainly, many young cancer patients on various protocols do receive many follow-up studies particularly positron emission tomography-CT fusion studies that may result in high cumulative exposures but we have elected to focus on patients with benign disease first. c. Study types: Five studies of the neck, chest, abdomen, or abdomen/pelvis that would expose the patient to a dose estimate of about 50 mSv. These are dose estimates, not calculations done by physicists, and we have therefore stayed away from using any sort of precise measurement and prefer to use the number of studies in our thresholds. This is in keeping with the difficulties that physicists have in measuring exact dosages in patients given the huge number of variables involved in this process.9,12 d. CT technologists: Our CT technologists have been empowered in this process to actively research imaging histories in the radiology information system (RIS) and report any suspicious histories to the radiologist on duty at that time and then to the RSO. The imaging history and studies are then reviewed and when the criteria are met, the patient is entered into our database of at risk patients. Once a patient is identified using the above system, the following events take place: a. The patient’s demographics are annotated in the RIS with the annotation of “Radiation safety alert/patient
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50
Figure 1 Sample requisition of “flagged patient.”
has had more than 5 CT studies/consult with radiologist” similar to contrast allergy. See Figure 1. b. Further studies on these patients are only performed with radiologist consultation to assess for clinical appropriateness, the suitability of nonionizing modalities for evaluation instead of CT, or overwhelming clinical indication. c. A certified letter is sent to the referring clinician and the primary care provider, when there is one, when the patient activates the 5 study threshold. This letter discusses the radiation safety issues and the potential risks of further studies. The practitioner is also informed of the necessity of radiologic consultation when further CT studies are needed. d. Although the patient has more than 10 studies listed
above, they are then placed in a higher risk category. In addition to the measures detailed above, a certified letter is sent to the patient. In the course of our development of this program, we have become aware that many of our patients have received care at multiple institutions where they may have additional radiologic studies. Patients in this category should be informed of these issues in a calm manner, so that they can take charge of their medical care, record their imaging history, and have a say in any future imaging. e. The RSO and our consulting physicist are made available for patient and provider consultation as needed. This program has met with high acceptance by patients, clinicians, and most radiologists. Patients and their parents
Radiation protection in the era of helical CT have thanked me for protecting them. The first patient whom we identified 5 years ago and is now 19 years old, has no subsequent renal stone CT studies, 10 renal ultrasounds, 10 KUB’s, and 1 one-shot intravenous pyelogram with a substantial diminution in radiation dose, no significant changes in the clinical management of his continued episodes of renal colic, and no adverse effect upon his health by limiting his CT studies. His urologist has enthusiastically embraced this program and frequently calls for radiologic consultation. The initial phases of this program have been performed in a tedious prospective manner as the patients have presented to our departments and are identified by the CT technologists or radiologists upon review of their imaging history. We are now picking up patients for our program with a more efficient and thorough method using data mining techniques in our RIS. We have been able to identify many more patients in this manner. We run quarterly reports with this technique and flag patients in our RIS and send letters as needed on that basis.
Monitoring a Patient Focused CT Radiation Safety Program Over the past one year, as our program was established we have monitored the results to assess its efficacy. The CT technologists have logged all cases where a flagged patient in the RIS has had a CT study ordered and the outcome documented after radiologist consultation. Fifty-one patients came to the attention of the CT technologists and radiologists in this program. The results of these encounters are as follows: 1. Eight of 51 studies were canceled. 2. Eight of 51 studies were changed to nonionizing modalities, such as ultrasound or MR imaging. 3. Thirteen of 51 studies were performed at the insistence of the clinician. 4. Twenty-one of 51 studies were performed after consultation between radiologist and clinician and agreement upon study indication. 5. One of 51 studies was performed at the insistence of the patient. Clearly this sort of program can decrease the volume and frequency of studies performed in patients who had multiple CT studies. However, most studies are still performed, often without strong clinical indication at clinician insistence, and without change in patient outcome. The need for further education and guidance is clear. These patients came from the following referral sources: 1. Emergency room providers-27/51 2. Hospitalists-10/51 3. Gastroenterologists-7/51 In the community hospital setting, the great majority of patients are either inpatients or emergency room patients, and this is where the focus of our activities has been. The gastroenterologists in our practice have readily adapted to
51 our recommendations and now frequently order MR imaging enterography rather than CT studies. Recent report points to a massive increase in population radiation dose from outpatient office CT and nuclear medicine procedures that we do not have access to in our systems. In conjunction with our CT radiation safety programs, we also have a vigorous hospital wide radiation safety program that includes the following items: 1. Monitoring of fluoroscopy times for all users of ionizing radiation. 2. Notification of the RSO of all patients receiving greater than 30 minutes of fluoroscopy during interventional procedures including cardiac catheterizations and operating room use, with examination of the patient for deterministic effects within 24-48 hours of exposure. 3. Credentialing of all users of fluoroscopy in radiology, cardiology, and the operating room coincident with hospital privilege recredentialing. 4. Mandatory attendance at radiation safety committee meetings of representatives of all users of radiopharmaceuticals and fluoroscopy in all areas of the hospital including cardiologists, pain management specialists and operating room nurses. 5. Quarterly radiation safety committee meetings with discussion of all the above issues. Through the use of all of these avenues, radiation safety in all areas of our hospitals has become a priority and not just an inconsequential after thought.8
Regional, State, and National Efforts There has been an increasing awareness of radiation issues from diagnostic imaging over the last 5 years as I began my work into this issue. In 2001, the FDA issued its first warning on the potential dangers of CT radiation exposure in children followed by a subsequent warning on the lack of efficacy and potential dangers of whole body screening with CT.12,13 In New Hampshire, the state radiology society was an early forum for my efforts. The reaction to my talks was mixed, although I was somewhat inflammatory in my efforts to draw attention to the issue that I had observed first hand. I have given over 30 talks in the state since 4 years. Over time virtually all the hospitals in New Hampshire have begun programs similar to ours with encouragement of the state society. The New Hampshire Medical Society was similarly supportive and encouraged my efforts. The State of New Hampshire has developed a trauma imaging subcommittee in the Department of Health to address the issues of CT radiation exposure in trauma patients (C. Odell, Concord, New Hampshire, August 2009, personal communication). In New York, the Commissioner of public health has sent a letter to every physician in the state warning of the potential dangers of profligate CT scanning.14 There are no government regulations that limit patient exposure to diagnostic imaging. All regulations are aimed at safe occupational expo-
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52 sure and the safe handling of radiopharmaceuticals. Too often, as an RSO, I have spent much time addressing state regulatory issues, such as where the positron emission tomographic patients may use a bathroom or the location of the treadmill in the exercise stress laboratory rather than the epidemic of diagnostic imaging radiation exposure. Although I do not relish government involvement in this issue, at this point, there may be no other alternative to stem this tide. Insurance companies have been involved in radiation safety initiatives over the period. In New Hampshire, Anthem Blue Cross/Blue Shield has used a data mining approach in their precertification process to alert practitioners to the potentially frequently exposed patient. They do not deny the study but instead use their thresholds to inform and educate clinicians. Anthem has also set up an extensive web site for both clinicians and patients to access information that is high quality and nonhysterical on these topics.15 My first inclination upon the initiation of this program was cynicism in that I felt they were trying to decrease use and imaging costs but the percentage of patients that fall into this area is relatively small and the infrastructure costs to anthem far exceed their savings in claims. National Imaging Associates, the largest radiology benefits manager in the United States, uses a similar system to alert clinicians to potential frequent radiation exposure (T. Dehn, Manchester, New Hampshire, personal communication). However, their system, which reports an estimated dose to the patient over time, is fraught with methodological issues in that dose per study is an extremely difficult parameter to measure on any 1 patient, given differences in patient body habitus, age, and scanning parameters. The American College of Radiology has taken an activist position on CT radiation safety. The College convened a Blue Ribbon Panel on this issue in December 2006 and produced a White paper in May 2007.16 This paper contained multiple recommendations for improving radiation safety, and its recommendations are steadily and surely being implemented over time. In addition, the American College of cardiology has also embarked on similar programs and recommendations.
Conclusions Radiation exposure to the United States population has increased dramatically over 15 years with advent of helical CT and expansion of some nuclear medicine procedures. Does irradiation from CT cause cancer? We don’t know. Although a single study in an elderly patient is of virtually no concern, younger patients with benign conditions may be regularly and frequently exposed to CT irradiation, often with not much clinical utility and change in outcome. It is imperative that all radiologists become active in the prevention and man-
agement of this epidemic. This epidemic is akin to global warming. All radiologists should have the political, social, and economic strength to manage this issue, as decisions we do or do not make now may come back to haunt us terribly in 10 to 15 years when radiation induced carcinogenesis returns to our society similar to the early 20th century when the dangers of radiation were not well known.
References 1. Birnbaum S: Helical CT: Too much of a good thing. BMJ 334:1006, 2007 2. McCollough CH, Bruesewitz MR, Kofler JM: CT dose reduction and dose management tools: Overview of available options. Radiographics 26:503-512, 2006 3. Li J, Udayasankar U, Toth TL, et al: Automatic patient centering for MDCT: Effect on radiation dose. AJR Am J of Radiol 188:547-552, 2007 4. Keyzer C, Gevenois PA, Tack D: Dose optimization and reduction in MDCT of the abdomen, in Tack D, Gevenois PA (eds): Radiation Dose From Adult and Pediatric Multidetector Computed Tomography. New York, NY, Berlin Heidelberg Springer-Verlag, 2007 5. Hopper KD, King SH, Lobell ME, et al: The breast: In-plane X-ray protection during diagnostic thoracic CT-shielding with bismuth radioprotective garments. Radiology 205:853-858, 1997 6. Hurwitz LM, Yoshizumi TT, Goodman PC, et al: Radiation dose savings for adult pulmonary embolus 64-MDCT using bismuth breast shields, lower peak kilovoltage and automatic tube current modulation. AJR Am J Roentgenol 192:244-253, 2009 7. Yousefzadeh DK, Ward MB, Reft C: Internal barium shielding to minimize fetal irradiation in spiral chest CT: A phantom simulation experiment. Radiology 239:751-758, 2006 8. Birnbaum S: Radiation safety in the era of helical computed tomography: A patient-based protection program currently in place in two community hospitals in New Hampshire. J Am Coll Radiol 5:714-718, 2008 9. European Commission: European Guidelines on Quality Criteria for Computed Tomography. Office for Official Publications of the European Communities, 2000, pp 70. EUR1626EN 10. Lee CI, Haims AH, Monico EP, et al: Diagnostic CT scans: Assessment of patients, physicians and radiologist awareness of radiation dose and possible risks. Radiology 231:393-398, 2004 11. Winslow JE, Hinshaw JW, Hughes MJ, et al: Quantitative assessment of diagnostic radiation doses in adult blunt trauma patients. Ann Emerg Med 52:93-97, 2008 12. Feigal DW: FDA public health notification: Reducing radiation risk from computed tomography for pediatric and small adult patients. Int J Trauma Nurs 8:1-2, 2002 13. United States Food and Drug Administration, Center for Devices and Radiological Health: “Whole Body Scanning Using Computed Tomography”. Available at: http://www.fda.gov/cdrh/ct. Accessed October 21, 2008 14. Daines R. Commissioner of Public Health for the state of New York, Letter to all Practicing Physicians in New York State, September, 2008 15. Anthem.com. Available at: http://www.anthem.com/wps/portal/ ahpprovider?content_path⫽provider/noapplication/f5/s2/t0/pw_ ad85140.htm&state⫽nh&rootLevel⫽0&label⫽Radiation%20Safety% 20Toolkit. Accessed August 30, 2009 16. Amis ES Jr, Butler PF, Applegate KE, et al: American college of radiology white paper on radiation dose in medicine. J Am Coll Radiol 4:272284, 2007