California’s Dose Puzzle Is Radiology’s Challenge
The imaging informaticists, physicists, physicians, and vendors’ representatives who gathered at the Society for Imaging Informatics in Medicine regional meeting, Practical Imaging Informatics, in Long Beach, California, on March 22, 2012, didn’t arrive in covered wagons, but they did have much in common with the state’s pioneer settlers. On September 29, 2010, California’s SB 1237 was signed into law as the Medical Radiation Safety Act,¹ effectively putting all providers of CT exams on notice that beginning July 1, 2012, they would be required to begin reporting technical parameters and radiation dose for each study.
Prompted by an outpouring of popular dismay over reported episodes of overradiation in California and elsewhere, the legislation does not mandate how much radiation is permissible—just that the dose be recorded in the PACS and the radiology report, and that incidents of overradiation be reported. The public, however, is unlikely to be much interested in the nuances of the law, according to J. Anthony Siebert, PhD, professor of radiology at the University of California–Davis, who moderated the “Radiation Dose Monitoring in California” sessions. “Individual patients see this, and now, they are wondering what their dose is,” he says.
Therein lies the rub. While there are measurements of volumetric CT dose index, dose–length product, effective dose, and absorbed dose (among others), there currently is no way to calculate and send the patient’s dose to PACS automatically, robustly, and accurately. California providers of CT exams and radiation therapy are bound to comply with the new act; the challenge is how to do so. Even the most advanced and conscientious providers are struggling to overcome the limitations of technology, informatics, personnel, and the science of dosimetry.
With radiation dose increasingly on the radar of regulators and payors nationwide, imaging stakeholders are well advised to join the pioneers in California who are seeking answers to a very complex problem: What is the best way to calculate patient dose?
Along with Siebert, four other presenters addressed this question. Bette Blankenship, MS, DABR, is a medical physicist at Sharp Memorial Hospital (San Diego, California). Christopher Cagnon, PhD, DABR, is chief of radiology physics at the University of California–Los Angeles (UCLA) Medical Center. Michael McNitt-Gray, PhD, DABR, FAAPM, is a professor in the department of radiological sciences of the David Geffen School of Medicine at UCLA.
Together, these three presented “Radiation Dose in a Clinical Environment: Benefit and Risk—The User’s Perspective.” Lisa Russell, inspector, compliance and enforcement, for the California Department of Public Health (CDPH), then presented “The California Dose Reporting Law: Implications and FAQs—The Government’s Perspective.”
With enactment of the Medical Radiation Safety Act, California providers have been pushed beyond the debate over the relative risks of medical radiation. In referring to the issue of radiation exposure, Seibert notes that many of the reported incidents have been due to human (rather than technological) problems, in terms of using the equipment properly and safely. He does, however, acknowledge the stochastic risks of ionizing radiation seen with extremely high doses, as at Hiroshima and Nagasaki, Japan.
“What are the risks of cancer induction and the stochastic characteristics of ionizing radiation?” he asks. “It’s a weak carcinogen—but remember, it is a carcinogen. We have to understand that epidemiologists love to take very, very low risk multiplied by really, really large numbers of patients, and then you have all of these virtual cancers and virtual deaths that occur. Is that a reality? Well, we don’t really know, but we do have to pay attention to it.”
The issue is unlikely to go away; in fact, Cagnon predicts that the next big regulatory flashpoint in imaging will be fluoroscopy. “There’s been a shift in users of fluoroscopy from the traditional realm of radiology and radiation oncology into operating rooms and physicians’’ offices,” he notes, also citing a shift in the types of procedures (from diagnostic to therapeutic). “In the catheterization laboratory, what was once a five-minute procedure can now be hours long,” he adds.
What Physicists Measure
“Everyone wants to know what his or her dose is,” Cagnon says. “It’s a frequently used term, and it’s frequently used incorrectly.” Radiation dose has several meanings and can be expressed in multiple ways, using different units. There is no book of standard doses for medical exams. Dose received by a patient spans a wide range, depending on what is done, the procedure parameters, and the equipment used. There is no single dose measurement that does the greatest job of describing risk.
What physicists measure, Cagnon explains, and what machines report, is almost always referred to as exposure. Physicists expose an ion chamber to ionizing radiation and then measure the charge that results. This charge is known as kinetic energy released in matter, material, or unit mass (kerma). Some machines report air kerma or kerma area (dose area) product.
The measurement methods for exposure and dose, however, have the least relevance for patients. More biologically relevant measurements that can be more useful for calculating risk—absorbed dose, dose equivalent, and effective dose—require some calculation by the physicist.
While absorbed dose might be more relevant, it, too, has its limitations. To emphasize that dose is independent of the volume of material irradiated—and is, therefore, not a definitive measure of risk—Cagnon likes to ask his radiology residents the following question: If a single 10-mm CT slice generates a dose of 2 cGy, how much will 20 consecutive slices generate?
The answer is the same—2 cGy—but the biological risk of the multislice study is, of course, greater. “Dose only tells us how much energy was absorbed by the material/tissue that was actually irradiated; it doesn’t tell us how much tissue was irradiated or provide the total (integral) radiation dose received by an object,” Cagnon explains. “We all know that the actual biological risk is greater, but the dose, which is what everyone uses, does not necessarily tell you that,” he adds.
Dose equivalent, another measurement used by physicists, refers to the fact that various forms of radiation have different biological effects. Dose equivalent equals the absorbed dose multiplied by a quality factor. This factor is around 1 for beta particles, gamma rays, and x-rays. For protons, it is much higher, at 5; for alpha particles, it is 20.
Effective dose requires another calculation that takes into consideration the biological sensitivity to radiation of the body part irradiated. For instance, Cagnon explains, a very high dose to the fourth finger might burn the skin, but the effective dose would be considered quite low because there aren’t any biologically sensitive organs in the finger.
Ironically, an argument could be made that patients subjected to the high-dose head-CT exams featured in widely publicized photographs of hair loss—photos that helped launch SB 1237—were actually the subjects of effective doses that were quite low. “The brain is not considered to be a critical organ, from a radiation-sensitivity point of view,” Cagnon explains.
On the Head of a Pin
Some physicists are famous for hairsplitting scenarios, but it doesn’t take a lot of imagination to envision the confusion and chaos that could ensue if patients start comparing radiation measurements of different types, believing them to be an accurate reflection of patient dose. Imaging devices, themselves, report different kinds of measurements. Radiography and fluoroscopy machines report exposure, air kerma, and dose, but whether that is dose to the skin or air dose is something that physicists almost always have to reverse engineer.
CT, the object of the Medical Radiation Safety Act, is unique. The tube (or source) travels around the patient in a circular fashion, so the dose in a range of slices is actually more uniform than it is for a projectional exam of the same body part (for example, a chest radiograph). In addition, the dose from a study that scans a volume of the patient is higher than the dose from a single, thin slice of anatomy because it incorporates scatter from one slice into the next. CT dose index is the absorbed dose to a 16-cm or 32-cm phantom. Volumetric CT dose index—one of the measurements that CT systems report—is computed by dividing the weighted CT dose index (the weighted average of the center and peripheral measurements within the phantom) by the pitch (or table movement).
CT systems also report dose–length product, an attempt to incorporate how much of the body is irradiated (something that volumetric CT dose index does not do). For instance, if you perform a scan that covers both the chest and the abdomen using the same technique, the volumetric CT dose index is the same as if you did only one region, but the dose-length producr would be higher (because of the greater length of the scan) when you scan both regions. What dose–length product does is multiply the volumetric CT dose index by the scan length. Using the example of the chest and abdomen scans, a dose–length product of 120 mGy-cm (for three 4-cm slices) becomes 360 mGy-cm (for nine 4-cm slices).
Neither volumetric CT dose index nor dose–length product, however, is an accurate representation of patient dose. By using published data obtained through Monte Carlo modeling of an idealized (geometric) patient, the dose–length product is multiplied by a coefficient (specific to the patient’s age and the body part) to arrive at an estimate of effective dose, which is an estimate of the stochastic risk of carcinogenesis due to the radiation associated with the study. However, this estimate does not account for variations in patient size.
Another dose-estimating tool also uses a mathematical model of the body to estimate dose. ”I can plug in parameters, but if the patient varies in size and shape from the assumed mathematical model, the estimates are going to be more and more inaccurate,” Cagnon says.
A final complicating factor is that all of the information reported by a CT system is based on phantoms, not patients. Cagnon says, “Patients are not standard; they are not cylindrical, and they are not homogeneous.” Volumetric CT dose index tends to overestimate doses for larger patients and underestimate them for smaller (including pediatric) patients.
A patient with twice the dose–length product or volumetric CT dose index of another patient does not necessarily receive more dose because a larger patient has more tissue to absorb the energy. Dose–length product underestimates the dose for exams where there is no table movement. CT dose index overestimates the dose for stationary exams by approximately a factor of two.
CT dosimetry is still very much a work in progress, Cagnon says. Ongoing work includes adjusting CT dose index for patient size, accounting for tube-current modulation (a feature used on nearly all modern CT systems that adapts output to patient size), and performing Monte Carlo modeling that produces more realistic results.
Right now, California’s providers would settle simply for the ability to have the DICOM Radiation Dose Structured Reports (RDSRs) or patient protocol go directly into the radiologist’s report from the CT system, Cagnon says. Not only would it prevent radiologists from having to dictate that number into the report, but it would put the number in front of radiologists—to create awareness of dose. “I want them to have that number; I just have to train them not to call it patient dose,” Cagnon says.
One key data point missing from the reported CT-system numbers that is a barrier to reporting patient dose is patient size, according to McNitt-Gray. “CT dose index is an index,” he explains. “It is dose in a phantom; it has lots of good uses. We’ve been using this for almost 40 years, to very good effect. It’s a great measure of scanner output, it’s a good index when comparing protocols and technical parameters, and it also is a good indicator of how scanner output is being adjusted with patient size.”
In clinical practice, he notes, CT-system output is increased for large patients, and decreased for small/pediatric patients, so the volumetric CT dose index will be larger for the bigger patient than for the smaller patient. Based on the volumetric CT dose index, one could presume that the larger patient received twice the dose that the smaller patient received.
“Actually, that’s not true,” explains McNitt-Gray. “The scanner output was higher, but the absorbed dose was not increased by a factor of two.” A task group² (which included McNitt-Gray) of the American Association of Physicists in Medicine (AAPM) developed a method to account for patient size—using effective diameter, lateral width, or anteroposterior thickness—when estimating dose.
Volumetric CT dose index still can be somewhat troublesome in several situations. Since volumetric CT dose index is a weighted average of measurements made at the periphery and center of a cylindrical phantom (allowing for the scatter that accrues with table movement), it actually overestimates skin dose to patients who are undergoing scans without table movement, such as the brain-perfusion scans that played a pivotal role in launching SB 1237.
McNitt-Gray reiterates that volumetric CT dose index and dose–length product are not patient dose—and when taken by themselves, can be misleading: “You need other information, such as the patient’s size, body region, and clinical indication, to determine if a scan was done correctly,” McNitt-Gray says. “That’s not always available or captured in dose reports.”
According to McNitt-Gray, it also is important to know the size of the phantom that the vendor used to calculate dose: Currently, all vendors use a 16-cm phantom to calculate volumetric CT dose index for head studies, and all use a 32-cm phantom to calculate it for adult body studies. Small-adult and pediatric studies get a bit tricky: Two vendors use the 32-cm phantom and two others use either a 16-cm or 32-cm phantom, based on the scan field or the patient size.
Volumetric CT dose indices, depending on whether the 16-cm or 32-cm phantom is used, will vary by a factor of 2 or 2.5, depending on the scan. “If you guess the wrong phantom, those numbers are going to be very high or very low, and that is going to affect the dose–length product as well,” McNitt-Gray explains.
Nonetheless, beginning July 1, something about dose must be placed in the medical record. McNitt-Gray says, “We know how to do this, from a physics point of view, for an odd case. To make it really generalizable and powerful for all of the patients we see—and to comply with state laws—we really need informatics solutions.”
All California facilities performing CT exams will be required to send each CT study and protocol page that lists the technical factors and radiation dose to the PACS, if the CT system has that capability. The new law says that the protocol page or the DICOM RDSR will meet this requirement.
“As long as we take that from the scanner and push that patient protocol page or the DICOM RDSR to our PACS, boom: We are in compliance—done,” McNitt-Gray says. It does get trickier, though. The law also mandates that the radiology report of a CT study include the radiation dose, either by recording the dose in the report itself or by attaching the protocol page to the report.
Many older CT systems are still in use in California, and not all of them are capable of producing a CT DICOM RDSR, raising a thorny question: Who will take the time to input the dose measurements manually into the radiologist’s report? The law also stipulates how the dose is defined: either the volumetric CT dose index, the dose–length product (both of which have their limitations), or a dose unit recommended by the AAPM.
“The AAPM has not spoken on this,” McNitt-Gray reports, “so we are stuck with volumetric CT dose index or dose–length product for July 1, and we’ve got to get that in, which is a little bit of a problem. Not all scanners are capable of generating the RDSR; it’s out there, and the manufacturers all have it, but we don’t have it on all of our scanners.”
If some of the leading physicists in academic medicine are struggling to find a satisfactory way to meet the letter of the law, it is somewhat disconcerting to imagine the challenge for a rural community site without physics support, even with an extra six months to comply.
As a 2007 Malcolm Baldrige National Quality Award winner, Sharp HealthCare (San Diego, California) is hardly a backwater. It does, however, offer a great example of a community hospital taking a proactive approach to meeting the demands of the law, resulting in some significant dose efficiencies.
Blankenship reports that the health-care system took the opportunity to review, evaluate, and revise all of its more than 700 CT protocols. She explains, “We verified the doses, we verified that they were within a reference value that was acceptable to our radiologists, and we asked, ‘Can we do more? Can we pull more dose out of these and have a reasonable and excellent image for the radiologist to read?’”
Through this exercise, Blankenship had an epiphany: Sharp Memorial Hospital had way too many protocols in place, none of which were the same. Working from exam to exam, reducing dose little by little “until the radiologists screamed,” she says, Blankenship was able to reduce dose for head protocols by an average of 35%; for neck protocols, by 60%; for chest protocols, by 43%; and for abdomen/pelvis protocols, by 45%.
Blankenship also recognized the need to go back to the technologists at the CT systems, reinforce their training, and make certain that they understood the meaning of a reference value. Relying on guidance from the AAPM3,4 on what constitutes a red flag when viewing a dose page, she spent time clarifying when technologists should call for help, at the outset of an exam, if they encountered a variable greater than what they were used to seeing,
The next challenge addressed was how to get the dose measurements into the RIS (for the radiologists to include in their reports). Purchasing analytics software is the current goal for Sharp Memorial Hospital, but the interim (time-consuming) step is for technologists to document manually the dose variables used in each study.
While the dose pages are automatically pushed to the PACS, where radiologists have access to the dose data when reviewing images, there currently is no way to send those data from the CT system to the RIS automatically. Currently, technologists access the dose measurements documented on the dose page and manually enter the volumetric CT dose index and the dose–length product into the RIS, which then automatically populates the physician’s dictated report with that information. “It’s very time consuming, especially when you’re doing trauma, and you have 60 patients you’re pumping through a CT scanner,” Blankenship emphasizes.
Essentially, what the Medical Radiation Safety Act did was add amend/add four sections—111, 112, 113, and 115—to the California Health and Safety Code, intended to govern the safe use of CT for diagnostic purposes (as well as the use of therapeutic x-ray systems operating at energies of less than a million electron volts). It does not specify how much radiation a procedure should deliver, but it does set limits beyond which a facility must report the event to the state, the patient’s physician (both within five days), and the patient (within 15 days).
Russell says that the state is not dictating the practice of medicine. “The California law and regulations don’t limit how much radiation a patient can receive,” she states. “That’s still a call of medical necessity, so that’s the physician’s call. We’re not saying that if you have a head CT that goes over x dose or dose indicator, you have to report it. We’re looking at excessive dose—extra dose—dose that wasn’t intended for the diagnostic purpose.” The law does stipulate reportable events (see figure).
Russell is quick to point out that the state recognizes that there are legitimate reasons for a repeated exam. “If the patient moves, either voluntarily or involuntarily—due to a seizure, for instance—then that is not considered a reportable event,” she says. “If the patient, caregiver, or anyone who’s required to be in the room with that patient during the study interrupts the study or (due to abnormal patient anatomy) if the protocol was followed using the proper landmarks, but you didn’t get the right parts in there, that’s still not going to be considered a repeat. We’ll consider that patient interference because everything was followed appropriately.”
If a physician, including a radiologist, orders a repeated exam, then that is not a reportable event, Russell emphasizes. “If your contrast doesn’t arrive at the right time, you miss the bolus, and the radiologist says, ‘Do it again,’ that’s not reportable,” she explains.
The law also raises the quality bar—as well as regulatory hurdles—for all CT providers by requiring facility accreditation, taking it a step beyond the Medicare Improvements for Patients and Providers Act of 2008. Beginning July 1, 2013, all facilities that perform CT exams—not just those billing Medicare and Medicaid—must be accredited by an accrediting body used by CMS (the ACR®, the Intersocietal Accreditation Commission, or the Joint Commission) or as designated by the California Department of Health Care Services (DHCS). To date, the DHCS has not received any requests from interested parties.
Five days is a short time in which to report an overradiation event, but the DHCS does not expect War and Peace, Russell says—just an initial report that includes a brief summary of what happened, to whom it happened, and when it happened. The report must include contact information for the person filing the report, the date of the event, the equipment specifics, the software version being used, and the technical factors involved in the exam.
The DHCS will make compliance inspections, as well as following up on all reported events, Russell promises, and it will verify that appropriate policies and procedures are in place. The investigator will want to know who determines which protocols are used in CT and therapy, how they are modified, when they are modified, and who approves modifications.
The investigator will also want to know whether the physicians have training for the studies that they are reading and whether the technologists have specialized training for the technology that they are operating, “especially if you have a number of CT units from various vendors, and the technologists are moving among them,” Russell says.
The investigator will ask to see the last physicist’s report on the CT system. “We want to see if the physicists identified any issues or concerns,” she continues. “We’ll want to see corrective action by the facility, and we want to see how the facility addresses those issues and concerns.”
The investigator will ask to see the CT console to be sure that a reference chart is available, with anticipated values and trigger values, so that technologists know when to raise the red flag about a potential event. “We want to see that the scanner displays the required values and how the technologists verify that the patient is the correct patient,” she continues. “We want to know when the technologists should seek guidance or additional authorization, from whom, and by what method. That should be very clearly outlined and, always, the technologists should be aware of it, especially if they’re working at night or on weekends.”
Other items that the DHCS will want to see following an event include dose reports in PACS, dose values in the radiologists’ reports, the methodology and calculations that the physicist uses to arrive at patient dose, copies of any internal reports on the event, and your corrective action (or plan to prevent a repeat of the event).
An Ounce of Prevention
It’s clear, from Russell’s presentation, that the Medical Radiation Safety Act will usher in a new era of awareness of dose on the part of CT providers in California, from the CT suite to the executive suite. “One of the lessons we’ve learned so far, from voluntary reporting and the frequently asked questions we’ve had, is that an ounce of prevention goes a very, very long way in keeping you from having to report to us,” she says.
“Do your training, to be sure that all staff members understand the equipment and protocols—so when they are putting someone in feet first, they don’t forget to change the kilovoltage,” she says. “Make sure everybody understands what you’ve got, and make it simple. Simplify protocols as much as possible, establish the trigger levels, and post them right there, so people will know when there might be an event. You don’t want to come across an event that happened last month when somebody’s doing monthly quality assurance—and then have to deal with it, when they don’t even remember what happened.” Inevitably, mistakes will happen, so everyone needs to know what to do in that event.
While the legislation does not specify optimal radiation levels, Russell says that the DHCS is looking for them. “We are hoping that everybody is working to use the least amount of radiation necessary to perform adequate imaging, and this is one of the things we’re looking for—hoping for,” she says.
Russell believes that success will hinge on hospital-administration support. “That’s especially important when you’re looking at services that report to different administrators—for surgery, for cardiology, and for radiology,” Russell notes. “Sometimes, it goes all the way up to the administrator before there’s a common denominator.” To become compliant across the board, Russell recommends, hospitals should appoint a patient-safety committee and a radiation-safety officer to examine internal processes, and they should loop in risk management and the physicist.
“Some facilities have actually established dose-reduction committees, and they have done some phenomenal work in lowering the doses, simplifying the protocols, and making the referring physicians aware of what they’re asking for (when they’re asking for it),” she reports. Russell urges providers to do an internal audit of processes and protocols, with an eye toward simplifying protocols and making them uniform.
“You can have a consultant come in and audit to give you an assessment,” she says. “The vendors have some fantastic products, and they can give you a lot of guidance on how you can improve. The people who have taken advantage of that, from what we’ve seen, are a lot more successful—not only in reducing their doses, but (when they do have an event) in explaining what happened, what went wrong, and how they fixed it. You don’t really want to rely on us and your compliance inspection as your external audit process, but some people do.”
Putting the Law Into Practice
In order to guide technologists in complying with the Medical Radiation Safety Act, Blankenship developed a flowchart to guide technologists’ responses to such questionable events as repeated exams and higher-than-normal dose values. The technologists’ concern is being able to identify a reportable event. “They’re beginning to understand that everything needs to be reported internally for evaluation and training purposes, but to get to a reportable event, I think most of us agree, it’s going to take quite a bit.”
Reporting on outlier studies is a key to Blankenship’s compliance plan at Sharp Memorial Hospital. She reports (to the radiation-safety committee and the quality council) all studies that exceed a reference value specific to a body region. Happily, she is down to zero reports, but that has not always been the case.
In order to track past compliance, Blankenship pulled every CT study since 2010 and discovered that 13 to 15 patients per month had been imaged inefficiently and outside the established protocol design. “I wanted to know why,” she recalls. “Now, in 2012, we’re down to zero on every single scanner.”
Judging by Blankenship’s experience, California’s Medical Radiation Safety Act has had a transformative effect on service delivery at Sharp Memorial Hospital. Protocols have been reviewed and streamlined. Reference values have been posted. Technologists have been trained to report exams outside the reference values and to enter the dose measurements into the RIS.
Still, there is the problem of getting the dose measurements into the radiologists’ reports. Blankenship says, “Someone shared with me that when they have somebody do something manually, you can count on a 17% error rate.” Addressing informaticists and vendors, she adds, “It is a step we are hoping you are going to help us remove.”
1. Bill number SB 1237: chaptered bill text. Official California Legislative Information. http://www.leginfo.ca.gov/pub/09-10/bill/sen/sb_1201-1250/sb_1237_bill_20100929_chaptered.html. Accessed June 15, 2012.
2. AAPM Task Group 204. Size-specific dose estimates (SSDE) in pediatric and adult body CT examinations. http://www.aapm.org/pubs/reports/RPT_204.pdf. Published 2011. Accessed June 19, 2012.
3. AAPM Task Group 23. The measurement, reporting, and management of radiation dose in CT. http://www.aapm.org/pubs/reports/RPT_96.pdf. Published January 2008. Accessed June 18, 2012.
4. AAPM Task Group 111. Comprehensive methodology for the evaluation of radiation dose in x-ray computed tomography. http://www.aapm.org/pubs/reports/RPT_111.pdf. Published February 2010. Accessed June 18, 2012.