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Editorial |
1 From the Department of Radiology, University of California Davis Medical Center, Imaging Research Center, 4701 X St, Sacramento, CA 95817. Received June 1, 2004; accepted June 2. Address correspondence to the author (e-mail: jaseibert@ucdavis.edu).
Index terms: Dosimetry • Editorials • Fluoroscopy, 32.1267 • Radiations, exposure to patients and personnel • Spine, vertebroplasty
Vertebroplasty and kyphoplasty are fluoroscopically guided percutaneous procedures for stabilizing vertebral fractures with the injection of polymethylmethacrylate into the vertebral column for the alleviation of persistent pain associated with compression (1–3). As more than 700 000 compression fractures occur yearly, of which approximately 280 000 cause severe pain and 150 000 require hospital admission (4), the use of these procedures is increasingly common in interventional radiology, neurosurgery, and orthopedic surgery. The procedure is clinically effective, and up to 95% of patients with painful compression fractures achieve substantial improvement in symptoms and function (1), although long-term results have yet to be fully described. A search of the MEDLINE database in May 2004 for articles related to "vertebroplasty OR kyphoplasty" in the "all fields" category yielded 374 articles, the majority of which had been published in the past 5 years, although some dated from 1985. A repeated search with the word radiation added for all search fields as a logical "AND" yielded 16 of 374 articles, of which only five (5–9), or approximately 1.3%, were pertinent to the discussion of radiation dose to the patient and radiation protection for support personnel during fluoroscopy. This result suggests either a lack of knowledge about these issues or an indifference to them. The fact that the majority of the 374 articles were published in nonradiology journals suggests the possibility that procedures are being performed without extensive training in or understanding of fluoroscopic imaging equipment, related radiation doses, and safety issues.
Typical effective and gonadal doses received by patients who undergo fluoroscopic vertebroplasty or kyphoplasty are estimated with dose-area product (DAP) meters and normalized conversion tables generated from anthropomorphic phantom experiments, as described by Perisinakis et al (10) in this issue of Radiology. This work illustrates the usefulness of radiation monitoring tools such as DAP meters for determining effective dose (11). Perisinakis et al used anthropomorphic phantoms and embedded thermoluminescent detectors in a series of exhaustive experiments to measure local organ doses for a specific examination (vertebral body and projection) and then correlated local doses with DAP values for the particular examination. Because DAP readings, roughly speaking, are independent of distance from the x-ray source to the patient, correlate with field size, and depend on the fluoroscopic technique used, DAP readings from fluoroscopy performed with different systems in patients similar in size to patients in the study by Perisinakis et al can be used with the authors’ DAP-normalized conversion tables to estimate with reasonable accuracy the effective and gonadal doses at vertebroplasty or kyphoplasty of a given vertebra. Risks of long-term stochastic effects such as cancer induction and adverse hereditary effects can then be determined.
Deterministic radiation injuries such as skin erythema, which occurs at a threshold dose of approximately 2 Gy, are of more immediate concern to the patient and have recently been the subject of intense scrutiny and regulatory oversight in the United States by the Center for Devices and Radiological Health of the Food and Drug Administration (12–14). Measurement of peak skin dose for fluoroscopic procedures is the key task, but accurate evaluation can be difficult and elusive. Peak skin dose depends on distance between the focal spot and the skin, tube voltage, tube current, and accumulated fluoroscopic exposure time for a given irradiated area. These parameters, including the irradiated skin area, can all change during the procedure. While it might be thought that DAP meters are useful for this task, entrance skin dose from DAP readings can be computed only for a specific dose rate, field size, and distance (11), making DAP measurements inadequate and prone to considerable error. Recognizing these deficiencies, Perisinakis et al (10) measured normalized entrance skin dose rates based on the anthropomorphic phantom imaging data, whereby simple measurement of accumulated fluoroscopic time and the multiplication of that value with the normalized dose rate value are all that is needed for determination of skin dose. However, a failure to attend to the associated caveats in the article could lead to considerable error in the skin dose estimate. Consider this a case of "You really don’t know what you are doing unless you know what you are doing" (15). While the intention is to illustrate fluoroscopy time thresholds for possible skin injuries (ie, how much time it takes to reach a total dose of 2 Gy) by using normalized skin entrance dose measurements, these data may not necessarily be relevant to other clinical situations that differ in equipment, patient size, and/or acquisition geometry. Of course, the use of an automated method such as skin dose mapping (16) to measure changes in tube voltage, tube current, exposure time, beam area, and beam position during the procedure and then to immediately generate and display a skin dose map on a simulated patient model, is desirable. Even though such capabilities are not likely to be commonly available because of high cost and/or lack of interest (15), patient dose monitoring and documentation are essential. Development of normalized skin dose measurements (in grays per minute) for a specific fluoroscopy system, focus-to-skin distance, and patient size range (eg, small, medium, large), with assistance from a medical physicist, is recommended. Skin dose then may be estimated from the accumulated exposure time for each projection by using the methods detailed by Perisinakis et al (10) for vertebroplasty and kyphoplasty procedures.
Do the majority of fluoroscopy operators who perform vertebroplasty and kyphoplasty really know how to use fluoroscopy equipment to keep radiation doses as low as reasonably achievable? Are these individuals aware of the typical effective dose and skin dose to the patient, as well as the doses to themselves from scatter or inadvertent positioning of fingers and/or hands in the beam? In my opinion, there is a surprising lack of formal training in the physics of fluoroscopy and radiation safety for nonradiologists, who often are involved with high-dose fluoroscopy procedures that are risky not only to patients (because of possible acute radiation injuries and stochastic late effects) but also to the support personnel in the room (because of unnecessary exposure to scattered radiation). In addition, there are no federal laws that prohibit licensed physicians from performing fluoroscopy, and only a few states (California, Ohio, Oregon) require individual certification with an administered test, credentialing, or verification of American Board of Radiology certification prior to the use of fluoroscopy for medical procedures. While fluoroscopy training and/or certification may be required at many large hospitals and academic medical centers, the extent of such programs is likely insufficient to provide the solid majority of appropriately trained fluoroscopy operators needed to ensure patient safety through good fluoroscopy practices.
What should be done by the operator in charge of fluoroscopy procedures? At a minimum, (a) stress the importance of training for fluoroscopy and encourage optimization of exposure parameters (eg, strict collimation, pulsed fluoroscopy, last frame hold); (b) understand the risks to the patient in terms of acute (deterministic) and late (stochastic) radiation effects; (c) require and use devices such as DAP meters for all fluoroscopy units; (d) support the participation of medical physicists in establishing guidelines and procedures for determining patient dose; (e) provide methods to keep staff exposures as low as possible; and (f) ensure the periodic maintenance and calibration of fluoroscopy equipment.
Even though the mean skin dose and effective dose ranges (173–233 mGy and 8.5–12.7 mSv, respectively) reported for vertebroplasty and kyphoplasty are relatively low with an overall average fluoroscopy time of 10.1 minutes (10), one must understand that the results reported by Perisinakis et al (10) were obtained by experienced operators with good medical physics support. Others have reported fluoroscopy times ranging from 10 to 60 minutes for similar procedures (8)—times that, at the upper end, might result in a high patient risk for both deterministic and stochastic radiation effects. An operator with proper fluoroscopy and radiation safety training who effectively uses that knowledge will understand the major factors that affect patient dose and should be able to implement methods to keep the dose and the risk low, both to patients and to support personnel, without compromising image quality. The article by Perisinakis et al (10) provides information and direction that are important for the assessment of radiation dose and risk from vertebroplasty and kyphoplasty procedures and that can assist in the achievement of these goals. An increased awareness of the radiation dose and associated risks for all types of fluoroscopic procedures is certainly a good thing ... and, yes, fluoroscopy operators should want to know about radiation doses to the patient, as well as to themselves and their support staff.
FOOTNOTES
Author stated no financial relationship to disclose.
REFERENCES
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