Radiation Exposure in Dialysis Patients
Authors: David R. Pickens, Martin P. Sandler
Journal: Journal of the American Society of Nephrology (2011)

Doses of radiation from medical imaging procedures including fluoroscopy, computed tomography (CT), and nuclear medicine procedures can be substantial in certain groups of patients for whom the likelihood of repetitive studies is high. Today, there is increasing concern that multiple imaging procedures leading to cumulative radiation exposure may increase the likelihood of developing cancer in the future, particularly when radiation exposure starts at an earlier age. Among these specialized groups of patients are those undergoing dialysis while awaiting kidney transplantation. In a study reported in this issue of JASN, De Mauri et al.1 observed that patients who received renal replacement therapy (hemodialysis and/or renal transplantation) during a 3-year period had, in addition to the inherent risk for cancer, increased radiation exposure, placing them at a risk for cancer four times greater than the general population; cancer risk was 1.0 to 1.5 times greater during dialysis and 2.5 to 5.0 times greater after kidney transplantation. Adjusting for 23 patient deaths and six transplants, the study covered a total of 281 patient-years and measured cumulative effective dose (CED), which allows for comparisons or summation of radiation exposure generated from different kinds of images. Patients ranged from 18 to >70 years, with 65% being in the 50- to 70-year group; 63 were male. Eighty-two patients were prevalent with a median dialysis period of 4 years; the remainder initiated dialysis during the study period. Younger patients and those on the transplant waiting list had higher radiation exposure and annual CED. Study patients received a total of 1303 examinations: 848 conventional diagnostic radiologic images, 248 CT scans, 108 nuclear medicine studies, and 99 interventional procedures. CT examinations accounted for 19% of studies and 76% of total CED; within that group, abdominal/pelvic examinations accounted for 43.1% of the procedures, 73.2% of the CT radiation exposure, and 55.6% of total CED. A total of 7.6% interventional procedures generated 8.1% CED, and 8.2% nuclear medicine procedures resulted in 7.6% CED. Assumed risk factors for this study were derived from analyses of mortality data based on Japanese atomic bomb survivors exposed to radiation doses typical of two or three CT scans in adults, using a linear no-threshold model (LNT), which is not adjusted for factors such as rate of exposure or genetic repair. Although leading international scientific bodies believe that the use of the LNT model for estimating low-dose radiation risk is appropriate, many scientists contend that it is not supported by data at doses less than approximately 100 millisievert or at long-term dose rate up to at least 200 millisievert per year.2–5 However, the LNT model is still considered the most appropriate and conservative for the purposes of radiation protection.6 The authors cite studies by various authors to support their thesis that dialysis patients receive higher radiation doses than other chronically ill patients, further referencing the American College of Radiology white paper on radiation dose favoring more explicit tracking of CT-related exposures, including identifying exposures for specific populations, such as hemodialysis patients. The authors conclude that a significant number of non-notable findings or negative results present an imperative to rethink justification for repetitive CT examinations. Huda6 recommended that nonionizing alternatives should be considered and that the benefits should clearly exceed the risks of radiation exposure before CT examinations are performed. Furthermore, as diagnostic facilities implement measures to reduce radiation exposure, a reduction in the number of CT examinations should be accompanied by reduced exposures per examination when possible. This study is an example of what is often seen in patient care settings where individuals of varying clinical experience order diagnostic imaging procedures. De Mauri et al.1 do not specify whether attending physicians, fellows, or residents ordered the studies; whether there were consultations with imaging specialists; or how benefits versus radiation risks for the imaging procedures were defined. In general, certain types of procedures are often overused because they are relatively easy to perform and a large amount of information is provided very quickly. The particular example described here, that of CT scans, can produce substantial cumulative doses of radiation when used multiple times. The conservative approach to addressing the issue of cumulative radiation dose necessitates defining groups of patients who would be considered high risk for exposure to ionizing radiation. This group would likely include children because the potential for radiation-induced cancer is more likely over their lifetimes than in older patients. In circumstances in which clinical management appropriately requires multiple imaging procedures, careful monitoring of the cumulative radiation dose should be done and should be part of the patient's record so that careful considerations of further exposure can be properly documented during the course of treatment. Of fundamental importance is that the radiation-producing tests should provide a substantial clinical advantage to the patient that helps in the management of the disease. This has been a primary tenet of imaging procedures for many years and is particularly important in high-risk groups, such as dialysis and transplant patients. In addition to recording cumulative dose information and making it available to the ordering physician, it is prudent to have an imaging expert, such as a radiologist or a nuclear medicine physician, provide suitable recommendations for alternative types of studies. Review of ordered studies on any class of patients but especially on those identified as high risk for radiation exposure should be done by someone who understands the utility of an imaging procedure. This person, then, is in the position to recommend alternative but equally suitable studies that operate without ionizing radiation yet provide images of comparable value. Examples of alternative imaging modalities are diagnostic ultrasound and magnetic resonance imaging. Both of these imaging modalities provide exceptional images of various parts of the body that might otherwise be imaged using ionizing radiation. When exposure to ionizing radiation is believed to provide best information, several practical measures can reduce radiation exposure. The best possible protocol should be used, applying only minimal radiation to produce the desired image. Imaging protocols using inappropriately high levels of radiation should be eliminated or modified. In fluoroscopy, pulsed acquisition, last image hold, and other approaches using variable x-ray beam filtering can optimize the image while reducing patient dose. CT dosing should follow a predetermined protocol that is accepted as being appropriate for the type of study requested. CT examinations can take advantage of tube current control, iterative reconstruction, and careful collimation to reduce entrance exposures. The American College of Radiology publishes guidelines for many studies that can help standardize these imaging procedures. In the case of studies performed with radioisotopes, guidelines provided by the Medical Internal Radiation Dose Committee of the Society of Nuclear Medicine should be followed to minimize dose while ensuring good-quality images. Careful calculation of isotope requirements, new designs for collimation, and longer acquisition times can lessen patient doses in nuclear medicine studies. Recommendations from the U.S. Food and Drug Administration will likely lead to requirements for equipment to monitor, record, and alarm when doses for a protocol are beyond the specified thresholds.7 Whatever the type of study, doses should be carefully monitored during the procedure and recorded for easy reference on follow-up by incorporation of this information into the patient's medical record. Undoubtedly, some of these needs will require the modification of computer software that controls imaging systems and changes to database systems that record patient data so that cumulative dose can be made available for the medical record. The Society of Nuclear Medicine, the American College of Radiology, the American Association of Physicists in Medicine, the Radiologic Society of North America, the Society for Pediatric Radiology, and the American Society of Radiologic Technologists are among the groups that are highly concerned with radiation dose and proper use of radiation for imaging. Some have banded together to develop informational awareness programs such as the Image Gently program for pediatric imaging (www.pedrad.org/associations/5364/ig/) and the Image Wisely program for adult imaging (www.imagewisely.org). The objective of these web sites is to encourage practitioners to avoid unnecessary ionizing radiation and to use the lowest radiation dose for necessary optimal studies. Such programs provide advice and recommendations on ways to provide top-quality images with minimal delivered dose. Radiation appropriately used and calibrated provides great benefit to patients needing diagnostic images. However, proper knowledge of procedures, dosage, effects, alternatives, and expected results is imperative to avoid potential overuse. One must remember that the objective of imaging is to maximize patient benefit while minimizing the potential burden of further disease as a result of the procedure. DISCLOSURES None. We thank Janet C. Staley for expert editorial assistance.