Copyright © 2009 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Glenn R. Rechtine, MD, and Thomas Morgan PhD, CHP*,
University of Rochester Medical Center, Rochester, New York
Posted August 2009
The study by Biswas et al., titled "Radiation Exposure from Musculoskeletal Computerized Tomographic Scans," is very timely. The need to better educate the medical profession about radiation exposure is overdue. With advances in technology, we have become complacent about the effects of radiation. Over the years, the development of more sensitive x-ray film has resulted in less radiation exposure during radiography. Digital radiography does not decrease the radiation exposures per se but does reduce the need for duplicate examinations because the images are available electronically. Newer computed tomography scanners, including the 64-slice and 256-slice scanners, have the potential to result in dramatically increased radiation exposures. The paper by Biswas et al. only addressed the exposures that took place with a 16-slice scanner.
Orthopaedic patients are exposed to the highest radiation exposures during diagnostic computed tomography scanning and intraoperative fluoroscopy. The intraoperative exposure places the surgeon and operating-room staff at risk as well. All orthopaedic surgeons should understand the basic physics of radiographic imaging and the steps that can be taken to reduce exposures for the patient, staff, and surgeon. The European Union is discussing a plan that will require all physicians involved with fluoroscopy to take a two-day course in radiation protection.
Biswas et al. are quite correct in calculating the effective doses, as these are the doses that have been calculated on the basis of the susceptibility of the tissue being radiated. These numbers are a small fraction of the total exposure dose. The International Commission on Radiological Protection put forth a modification of these numbers in 20071. The new numbers are based on data that show more risk with radiation of breast tissue and salivary glands, with a subsequent reduction in the weighting of the gonads. These new calculations would increase the values for the cervical and thoracic spine and slightly decrease the numbers for the lumbar spine.
The values reported in this paper are dramatically higher than those previously reported for computed tomography of the spine2. When we compare these numbers against the reports by Preston et al.3 that a mean effective dose as low as 34 mSv may result in a significant increase in the mortality rate associated with the formation of solid tumors, there is a concern for increased cancer risk with computed tomography examinations. We should be especially concerned about multiple scans or the tendency to repeat scans with marginal indications.
I am concerned about the authors' conclusion that the magnitude of exposures to the extremities is trivial. While this is true from a carcinogenic point of view, the long-term effects of cumulative radiation to the extremities should not be dismissed. One study showed microvascular effects in the fingers of physicians whose exposures had never exceeded 50 mSv in any year during their careers4.
The most obvious conclusion from these data involves computed tomography examination of the elbow. Elbow and wrist computed tomography examinations should be done with the patient's arm positioned over the head, if at all possible.
The routine use of computed tomography in the examination of children should be reassessed, as the possible carcinogenic effects of radiation exposure are greater in young patients. Adolescents with back pain may be better assessed for spondylolysis with magnetic resonance imaging instead of computed tomography. As spiral and multislice computed tomography has evolved, we now use computed tomography scans for primary imaging of the cervical spine in the emergency room. The standard trauma order for computed tomography of cervical spine, chest, abdomen, and pelvis increases the lifetime cancer risk from 1 in 8,500 to 1 in 1,0005. In pediatric patients, it may be a better practice to use magnetic resonance imaging in the assessment of the cervical spine because of the high radiation doses and potential risks associated with computed tomography scans.
In the past, a lumbar computed tomography scan included only L3 to S1 unless otherwise ordered; now we scan the entire lumbar spine routinely. This may also explain some of the difference in the numbers reported in the paper by Biswas et al. and the numbers reported for lumbar computed tomography in the past.
Approximately 2% of cancers in the United States may be caused by radiation exposure from excessive use of computed tomography scans6. While the public is becoming more aware of these risks, it is currently not routine to discuss with patients the radiation exposures involved with the studies that we order. Several physician surveys have been done that show that more than 75% of physicians grossly underestimate the amount of radiation involved with computed tomography scans7. It is now mandated that the radiologist maintain records with regard to estimated exposures.
The authors appropriately ask the question as to whether abdominal computed tomography scans can be reconstructed to provide spine images. The thicker cuts done with abdominal computed tomography will not provide the same detail of a spine-specific computed tomogram. Is the additional radiation that is required for a spine-specific computed tomogram necessary? This is a subject that needs further study.
All practicing physicians and especially those ordering radiographs and computed tomography scans should be knowledgeable about radiation exposures and inherent risks. This is the reason that a licensed practitioner must order radiographic examinations. Unfortunately, our current system does not adequately provide licensed practitioners with the education necessary to make this judgment appropriately. This paper adds to the body of knowledge that is needed to assist our practices.
*The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
References
1. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP. 2007;37:1-332.
2. Heggie JC. Patient doses in multi-slice CT and the importance of optimisation. Australas Phys Eng Sci Med. 2005;28:86-96.
3. Preston DL, Ron E, Tokuoka S, Funamoto S, Nishi N, Soda M, Mabuchi K, Kodama K. Solid cancer incidence in atomic bomb survivors: 1958-1998. Radiat Res. 2007;168:1-64.
4. Tomei F, Papaleo B, Fantini S, Iavicoli S, Baccolo TP, Rosati MV. Vascular effects of occupational exposure to low-dose ionizing radiation. Am J Ind Med. 1996;30:72-7.
5. Richards PJ, Summerfield R, George J, Hamid A, Oakley P. Major trauma and cervical clearance radiation doses and cancer induction. Injury. 2008;39:347-56.
6. Brenner DJ, Hall EJ. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007;357:2277-84.
7. Rice HE, Frush DP, Harker MJ, Farmer D, Waldhausen JH; APSA Education Committee. Peer assessment of pediatric surgeons for potential risks of radiation exposure from computed tomography scans. J Pediatr Surg. 2007;42:1157-64.
|
