Tracking Radiation Exposure from Medical Diagnostic Procedures Workshop Report (2012) / Chapter Skim
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3 Workshop Summary
3 Workshop Summary
Pages 17-52
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. Both the CDC and FDA have been active in the discussions of tracking radiation exposures from medical diagnostic procedures.
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, aiming to promote safe use of medical imaging devices, support informed clinical decision making, and increase patient awareness. Charles Miller proposed that the workshop participants consider the following question: Is now the appropriate time to reconsider the impact of radiation doses from medical procedures?
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. A registry that fits this purpose is the ACR Dose Index Registry discussed in Sections 2.5.3 and 3.2.4.
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separated the issue of the measurement of population utilization of medical diagnostic procedures into two challenges: a) counting the number of imaging procedures performed on the population and b)
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study was conducted in 1980 by the FDA's Center for Devices and Radiological Health (CDRH) to estimate numbers and types of diagnostic imaging procedures performed in hospitals in the United States; no dosimetry data were collected.
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Surveys now routinely collect data regarding patient exposure, indicators of image quality, facility exam/procedure workloads, and staffing levels, as well as features of quality-control and quality-assurance practices, Dr. Spelic said.
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Census databases cover about 65 percent of the universe and include both hospitals and independent imaging centers. Time required for data collection depends on the modality.
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3.2.4 ACR Dose Index Registry The Dose Index Registry could serve as a source for both procedure counts and dose index measurements. Workshop committee member Richard (Rick)
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. At the time the workshop took place, about 300 facilities were in the process of participating in the ACR Dose Index Registry and more than 100 had initiated data submission.4 These facilities are of different types (academic, community hospital, multi-specialty clinic, freestanding center)
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. The ACR Dose Index Registry currently does not cover all imaging modalities.
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VA has taken several steps to minimize the radiation dose received by patients, including the requirement for a national dose registry, although it is not clear whether funds will be available to develop the software, Dr. Anderson said.
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A protocol optimization guide was written to reduce CT dose while maintaining image quality. The protocol explains the factors that control radiation dose, states the diagnostic reference levels, and provides alerts and notifications.
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, and transfer of patient files from one part of the country to another via inter-PACS links have improved both the public acceptance of medical recording and the technical possibility of systematically collecting radiation dose data. The crucial point is the necessity for a permanent patient identifier, which constitutes the major problem in countries where there are no permanent identification numbers for the patient population, Dr.
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3.4 FROM DOSE INDICES TO DOSE ESTIMATES Dr. Walter Huda (professor of radiology at the Medical University of South Carolina and workshop committee member)
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. 3.4.1 Radiation Metrics in Medical Imaging The two experts explained that the CT dose index (CTDIvol)
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Use of the effective dose also permits the radiation dose of diverse diagnostic procedures to be quantified and thereby made understandable to medical imaging practitioners, as well as the general population, he explained. Because the effective dose is directly related to the stochastic risk associated with a given diagnostic procedure, it also permits determination of the risk associated with a procedure.
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For example, a study conducted to evaluate the relative radiation risk of CT versus nuclear medicine evaluation for suspected parathyroid adenoma showed effective doses that were nearly equivalent between the two tests. However, analysis of mean organ dose and risk showed that the thyroid was the most radiosensitive organ affected by the CT scan, while the colon was the most radio sensitive organ affected by the nuclear medicine study (Mahajan et al., 2011)
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Another issue with extrapolations is that the exposures from the atomic bomb were acute while the exposures in medical diagnostic procedures are fractionated. However, current knowledge is that the effects of fractionation are not as big as initially thought, and therefore the dose and dose-rate effectiveness factor (DDREF)
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Recent studies suggested that for radiation exposure in middle age, most radiation-induced cancer risks do not, as often assumed, decrease with increasing age at exposure (Shuryak et al., 2010)
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, an interactive computer software that uses risk projection models to estimate cumulative lifetime cancer risks related to any low-dose radiation exposure (not exclusively from medical diagnostic procedures)
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The NCI investigators are currently working on making the program publicly available in 2012 by developing a web-based version. 3.5.3 Non-Cancer Effects Although risk of developing cancer is the primary concern following exposure to low radiation doses, non-cancer diseases may also be associated with exposure from medical imaging procedures.
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The benefits versus risks associated with medical imaging procedures are more often discussed with emphasis on the fact that the risks are often unknown.
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Lauer suggested national discussions for randomized clinical trials. A successful story and relevant example is the NCI-funded National Lung Screening Trial, which showed that helical-CT can be life-saving for early detection of lung cancer among heavy smokers (Aberle et al., 2011)
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Efforts like the ACR Dose Index Registry can help to inform understanding of how much doses can be lowered without compromising the image quality. Although lowering the doses could lead to lowering the potential associated risks, it was many times stated that the focus should be on dose optimization.
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Collaborating through the Medical Imaging and Technology Alliance (MITA) the manufacturers' main efforts fall under the following four categories: • Reduction of exposures through equipment hardware features • Standardization of dose reporting • Integration of radiation dose into reports • User training It was noted that vendors are too often expected to optimize protocols, making them universal rather than vendor specific and using common
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3.6.3 Dose Monitoring and Individual Risk Assessment Although they voiced no arguments against tracking radiation exposures or doses and dose indices for the purposes of justification and optimization, some workshop participants disagreed about the desirability of tracking for the purposes of individual dose monitoring and risk assessment.
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It is important that the physician is able to provide the answers by being familiar with the current status and limitations of radiation dose estimations and risks. Today, many physicians are not adequately familiar with the radiation exposure effects, and training is crucial.
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Although there was no obvious approach as to how the dose or risk would best be communicated to the patient, or which of the two parameters should be tracked and communicated, many workshop participants said that little would be gained by communicating dose index metrics with the patient, especially because dose index metrics vary by modality and therefore do not provide a uniform recording system. Seemingly more meaningful is translating the dose index metrics to doses or risks or communicating in some generic way the increase of risk per exam (for example a 0.3 percent increase on top of the 42 percent baseline cancer risk)
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Because the methods to estimate patient doses are not yet fully developed and it is uncertain which are the most relevant, it might be necessary to record all parameters and dose indices provided by a scanner. This is in agreement with the prototype used in the California's legislation (see Section 2.5.6)
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Instead, they relate to whether and how the history of exposure to medical radiation (e.g., too many CT exams in a patient's record) fits into the clinical decision of ordering the next exam that utilizes ionizing radiation.
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All requests for diagnostic imaging procedures that involve ionizing radiation have to be approved by a radiologist, and the process requires justification of the need for the test.22 The Patients' Perspective Gwen Darien discussed the patients' perspectives on the risks and benefits of radiation exposure from medical diagnostic procedures. As a cancer survivor herself, her perspective was that of the cancer survivor rather than the typical symptomatic or asymptomatic patient.
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At an institutional level, dose indices or dose estimates of a patient associated with a single procedure could be tracked, and possibly some institutions could track cumulative dose estimates from a single but not multiple modalities. In support of isolated institutional efforts to track cumulative dose estimates from a single modality of a patient, Dr.
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Dr. McNitt-Gray argued that as the natural experiment of the effects of medical imaging procedures that use radiation is happening, it would be wise to collect good dosimetry data.
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Current work in many laboratories focuses on patient-specific (i.e., age, weight, size, gender) organ dose estimations and resulting effective dose estimations.
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However, such a national effort is not likely to be implemented in the near future for many reasons, including lack of sharing of medical information across different health care facilities, lack of a unique patient identifier and integrated medical records, non-automated dose information collection processes, and data protection and patient privacy issues. Similarly, the current health care delivery system and cancer registration system precludes a longitudinal study of dose for large populations in the United States that are exposed to ionizing radiation from medical diagnostic procedures.
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• Implement informed decision support systems at all stages of patient care to optimize procedure use and ensure that only appro priate examinations are performed. • Have institutions and ambulatory settings implement or continue to implement comprehensive safety programs and educational tools promoting awareness of radiation doses.
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