More and more hospitals are considering adding PET scanners to their nuclear medicine imaging arsenal. And a variety of sites are taking a long, hard look at the prospect of PET-CT. As with any capital purchase, there are a number of variables to consider. How much will the equipment cost? Does the facility have the patient volume necessary to justify the purchase of a PET scanner? Does the hospital have the necessary in-house expertise to staff the new equipment? If not, is it possible to train or attract outsiders to the site? And how does an on-site cyclotron fit into the PET equation? A final variable that should be inherent in each phase of the decision-making process is radiation safety. How does the facility intend to insure the safety of PET technologists and patients?

Standard nuclear medicine radiation safety practices are a good place to start, but they are not the final answer for developing PET safety protocols. Kelly Classic, medical health physicist and administrator for radiation safety at Mayo Clinic (Rochester, Minn.), says, “Initially, vendors claimed PET safety and shielding requirements were not any different from standard nuclear medicine safety and shielding requirements. And it seemed to make sense at first.” But the reality of PET scanning is that it is in a class by itself as far as radiation safety and shielding are concerned. Christina Truelock, assistant chief technologist of nuclear medicine at Thomas Jefferson University Hospital (Philadelphia), confirms, “A PET scanner does require safety equipment and protocols above and beyond a what is used in a routine nuclear medicine department. A PET scanner needs heavier shielding, and technologists need to adapt their handling and radiation safety techniques.”

Still, the basic principles of PET safety and shielding do have their roots in good old-fashioned nuclear medicine safety and shielding. Scott Holbrook, chair of the PET Education Task Force for the technologist section of the Society of Nuclear Medicine (Reston, Vir.), explains, “Good radiation safety practices apply to PET and nuclear medicine in the same way. The same principles of physics apply.” However, there are few key distinctions between PET and nuclear medicine safety protocols; these distinctions represent a primary concern for facilities jumping into PET.

The quick tour of nuke med safety protocols
Standard nuclear medicine radiation safety practices boil down to three considerations-time, distance and shielding. Technologists need to limit their time of exposure to radiation sources and pay attention to their distance from sources and hospitals need to install and maintain proper shielding. Direct handling of radiopharmaceuticals is completed quickly, and techs are trained not to sit a patient or spend an inordinate amount of time with a patient. Regardless of training, techs are caregivers and Holbrook admits, “In standard nuclear medicine, it is not uncommon for techs to sit or stand the next to the patient for reassurance after injecting the radioisotopes is generally accepted.” The rationale is simple; it is somewhat acceptable for techs to be close to the patients because they are giving psychological care as well as completing the exam and most of the doses from patients for general diagnostic are very, very low.

Whether or not techs opt to hold patients’ hands, the principles of time, distance and shielding do keep most nuclear medicine technologists safe from overexposure. Truelock notes, “In general nuclear medicine, the exposure rate is minimal. Technologists generally don’t get overexposed.”

The National Council on Radiation Protection and Measurements (Bethesda, Md.) estimates that the average nuclear medicine technologist’s whole body exposure is about 400 mrem annually. Mayo Clinic separately monitors its PET and nuclear medicine technologists and reports that PET techs receive about three times the radiation dosage of nuclear medicine technologists. That figure may be even higher for inexperienced PET technologists. Holbrook says, “Techs will experience increased radiation exposure as they first move into PET, but a few months after beginning to work in PET it comes down to a more acceptable level.” The key point for any facility considering moving into PET is to start with a rigorous radiation safety protocol.

PET safety protocols
How can a facility insure the safety of its staff as it implements a PET scanner? The same general principles of time, distance and shielding that apply in nuclear medicine are used but in a much more stringent manner. The difference is a matter of simple physics. The gamma emitters used for diagnostic nuclear medicine are actually fairly low-energy — 135 to 150-keV, which means there isn’t much exposure from the patient. PET, however, is a whole different ball of wax.

Mary Anne Dell, vice president of manufacturing and health physicist for Capintec, Inc. (Pittsburgh, Pa.), explains, “All PET isotopes, by definition, are positron emitters and have an energy of 511-keV.” The reality of high-energy emitters is that the radiation exposure coming from the patient is much higher for PET than nuclear medicine. Consequently, the room for error is smaller and some concerns that might be taken for granted in nuclear medicine cannot be overlooked in PET or the tech will be overexposed.

Simple measures can minimize tech’s exposure time. Holbrook avers, “It’s important to reiterate that the patient is where the tech can receive the most exposure.” Classic agrees. She adds, “Let’s face it. The patients are most technologists’ primary source of exposure. Reducing time spent close to patients reduces dose on the basis of time and distance.”

This workstation is used for the preparation of PET pharmaceuticals. Capintec’s workstation can be used instead of a shielded hood or hot cell.

In all hospitals, a radioisotope is carefully shielded before it is injected into a patient in order to prevent accidental exposure. Once the isotope is injected into the patient, it becomes an unshielded source of radiation. So a tech cannot opt to sit next to a patient for reassurance after injecting radioisotopes, or he or she will receive an undesirable exposure.

A typical PET scan requires anywhere from 30 minutes to 90 minutes of uptake time after injection. A tech can be potentially exposed during this span of time. The patient should be isolated in a shielded area during the uptake phase.

Nevertheless, a few sites designed their PET facility incorrectly and failed to account for technologists’ safety during the uptake phase. Jeff Clanton, DPH, director of radiopharmacy services and manager of the cyclotron facility for Vanderbilt University (Nashville, Tenn.), notes, “I’ve seen a few PET facilities that aren’t designed correctly. A PET site should have an isolated holding area for patients during the uptake phase. The holding area should be away from staff and other patients.”

While a hospital’s design may overlook safety during the uptake phase, individual technologists may slip into poor habits. Holbrook explains, “If a technologist injects a patient first and then starts asking questions and filling out forms, he will receive some exposure from the patient.” Another procedural no-no is to bring the radiopharmaceutical into the room prior to starting the IV. The tech should start the patient’s IV before bringing the radiopharmaceutical into the room. Glenn Sullivan, radiation safety officer for Children’s Memorial Hospital (Chicago), outlines the basic time and distance safety procedures for PET scanning.

• Bring the patient into the room
• Take the patient’s vital signs
• Prepare the radiopharmaceutical dose
• Calculate the specific activity needed
• Complete the scan, standing 10-12 feet away at the computer during the scan

Classic adds a simple guideline for PET techs to keep in mind: techs should stand a minimum of one to three feet away from the patient whenever possible.

Another potential PET safety concern is extremity exposures for staff members who prep and administer the radiopharmaceuticals. Shielded PET syringes do help reduce the dose to the body and hands. Clanton notes, “With PET radiopharmaceuticals you need to have the right PET syringe shields. The shields for standard nuclear medicine radiopharmaceuticals just don’t work.”

PETNet Pharmaceuticals tracks maintenance and service of one of its cyclotrons where FDG is produced.

Syringe shielding is just one part of the PET shielding battle. PET scanners require more lead shielding than standard diagnostic radiology rooms. For most diagnostic radiology rooms, 1/16 to 1/8 inch lead shielding suffices.

PET shielding requirements are calculated based in the size of the room, throughput of patients and types of procedures. Classic says a few manufacturers continue to insist that standard nuclear medicine shielding will suffice for a PET room; however, when most institutions complete these calculations they find that additional shielding. Mayo Clinic, for example, has 3/4 inch lead on its PET scan room walls. Some PET facilities also opt to invest in portable lead shielding for the technologist to stand behind if he or she has to be the in the room with the patient for a long time. Another option is to install lead shielding on the wall between the scanner controls and the scan room.

Some sites may be considering adding a PET-CT scanner in addition to or instead of a standard PET scanner. And while there are a variety of factors to weigh in the decision, shielding is not one of them. Classic explains, “The good thing about PET-CT is if you plan for PET shielding, the CT part is taken care of. The shielding requirements for PET easily cover CT.”

Monitoring is a key piece of PET radiation safety. Holbrook says, “It’s a good idea for techs to get radiation dosimetry badge readings on a regular monthly basis. If someone is doing something wrong you don’t want to wait two months to find about it.”

Although PET isotopes have a higher energy than nuclear medicine isotopes, they also have a shorter half-life. Standard nuclear medicine isotopes have half-lives ranging from six hours to one to two days, while PET isotopes have half-lives in the 15 seconds to 100 minute range. As a result, spill protocols differ. Typically, nuclear medicine spills are handled immediately. If a PET isotope is spilled, allowing the material to decay is an option because it decays relatively quickly. Holbrook says, “In the event of a spill, you may be better off covering the spill with lead shielding, closing off the area and cleaning the spill later.”

PET does have unique safety considerations; however, they are not at all insurmountable. Holbrook concludes, “The key to PET radiation safety success is finding good protocols and being very consistent with them. With training, a good nuclear medicine technologist can adapt to PET very easily.”

Regulatory requirements
It seems as if everyone has his or her fingers into the PET regulations. The Joint Commission on Accreditation of Healthcare Organizations (JCAHO of Oakbrook Terrace, Ill.), the U.S. Nuclear Regulatory Commission (NRC of Washington, D.C) and individual states all have some say in accreditation. And the really gung-ho may can explore voluntary PET accreditation through the Intersocietal Commission for the Accreditation of Nuclear Medicine Laboratories (ICANL of Columbia, Md.), which offers accreditation in PET imaging as well as nuclear medicine and nuclear cardiology.

JCAHO’s primary concern is general safety measures, so a JCAHO site visit may not be intensely focused on radiation safety. When it comes to PET and nuclear medicine, JCAHO generally looks at many of the same things it does in other areas of the hospital: proper management of the patient, medications handling, infection control issues, and fire and life safety. During a site visit, JCAHO may review employee exposure records and make sure that the radiation safety committee is meeting regularly. They also may look at staff training, orientation and certification records, and equipment calibration records.

NRC, on the other hand, is wholly focused on regulatory compliance and what a hospital does to comply with regulations. NRC does take an in-depth look at radiation safety issues, including radiation records, training and events, exposure records and radiation safety committee records. Classic notes, “NRC tends to be much more detailed than JCAHO [when it comes to radiation safety]. NRC seems to be changing. It used to be very paper-intensive, but during our last visit, they were more concerned with observing staff and watching procedures. It was more interactive than in the past.”

Finally, ICANL touts a number of benefits to its voluntary PET and nuclear medicine accreditation program. According to the organization, accreditation demonstrates a commitment to patient care and accountability, provides a confidential peer-review, and can be used as a recruiting tool. Regardless of the decision to pursue accreditation, however, radiation safety warrants a front seat when it comes to PET implementation.