A Nuclear Regulatory Commission draft regulatory guide—DG-8061, “Release of Patients Administered Radioactive Material”—proposes guidance on the release of patients after a medical procedure involving the administration of radiopharmaceuticals or the implantation of a sealed source. The guidance is intended to help licensees interpret NRC regulations designed to protect the people—family, friends, caregivers, or members of the general public—who may be in proximity to a patient who is discharged after receiving nuclear medicine treatment.
The draft guide offers a new dosimetry methodology that includes a conservative baseline threshold that assumes another person—a “bystander”—is near the discharged patient for 24 hours a day. It would replace the current guidance in RG 8.39, Revision 1, which assumes such a person is nearby for just one-quarter of that time, or, six hours in a 24-hour period. Licensees could choose to release patients only after they qualify under the new threshold—which could extend a patient’s hospital stay each time they undergo a cancer treatment. Or they could choose to use patient-specific data to calculate a more realistic estimate of the risk to justify the individual’s discharge—a process that may add to the costs of treatment and the time spent on each patient’s care, and possibly may restrict access to cancer treatments.
DG-8061 is a proposed Revision 2 to RG 8.39 of the same title, and it was released on April 21 for a 60-day public comment period that was later extended. That public comment period closes on Sunday, August 20; comments may be submitted through the federal rulemaking website at regulations.gov with a search for Docket ID NRC–2023–0086.
Guidance, not regulation: Importantly, the draft guidance is just that—guidance that describes methods that are acceptable to NRC staff for implementing specific parts of the agency’s regulations. Because regulatory guides are not regulations, compliance is not required by the NRC or the Agreement States.
The NRC’s “Patient Release Rule” (10 CFR 35.75) and accompanying RG 8.39, originally issued in 1997, allowed patients who had been treated with radioactive material to be released on dose-based criteria, with instructions to keep the total effective dose equivalent to bystanders as low as reasonably achievable (ALARA). The patient release regulations in 10 CFR 35.75—which are not being modified—allow a licensee “to release from its control any patient who has been administered radioactive material if the total radiation dose to any other individual from exposure to the released patient is not likely to exceed 5 mSv (500 mrem).” Additionally, licensees must provide written instructions to the patient to keep doses ALARA if the exposure to any other individual is likely to exceed 1 mSv (100 mrem) and must provide specific instructions if the total effective dose equivalent to a nursing infant or child could exceed 1 mSv (100 mrem).
Rules and revisions: A 2018 NRC staff review concluded that a “guidance update is needed as methodology in the guidance can underestimate potential dose to a member of the public in some situations.” That potential dose is mostly likely to be underestimated if the patient does not follow instructions to keep the dose to bystanders ALARA, and especially if the patient uses public transportation following discharge.
In fact, NRC staff found that “the dominant factor in determining both internal and external doses to members of the public from a released patient is the behavior of the patient once they have been released.” Nevertheless, “the NRC staff determined that timely and adequate patient discussions should be addressed in guidance and not specified in regulations because there is much variability between treatment procedures and patient situations. Thus, when to provide required instructions is a ‘practice of medicine’ decision.”
RG 8.39 is being updated in two phases. The first phase, Revision 1, was completed in April 2020 and included recommendations for pretreatment discussions and patient instructions. The second revision, the document now under public review, includes information for the administered activity and measured dose rate thresholds for commonly used radionuclides, calculational methodologies to accommodate threshold modifications for patient-specific exposure situations, flexibility for emerging radiopharmaceuticals that could be used for diagnostic or therapeutic purposes, radiopharmaceutical activity thresholds for patients who may continue breastfeeding an infant or child after administration of radioactive material (with recommendations for breastfeeding interruption times for typical dosages), and a new section titled ‘Sources Separated from the Patient.’
Two-tiered approach: The draft guidance introduces a two-tiered approach to patient release. Licensees can use “administered activity and measured dose rate baseline thresholds . . . to release patients without gathering patient specific information”; alternatively, “patient-specific information can be used to demonstrate release would comply with regulations.” Patient-specific information includes four factors: occupancy (how long will another person be near the patient?), geometry (how close would that person be?), attenuation (will the source be located deep in the body, such that the patient’s body provides some shielding?), and biokinetics (how will the radionuclide be biologically excreted over time?). Some of that information is obtained from the patient, and some is calculated by the licensee. All four factors can be adjusted (or not—conservative assumptions can be retained for some or all of the factors) in a formula that yields a more realistic bystander dose and a threshold that is likely higher than the baseline threshold, permitting patient release.
According to presentation slides prepared by the NRC for a July 20 public meeting, the baseline thresholds “used conservative [emphasis NRC’s] assumptions to ensure all released patients are not likely to cause exposure to other individuals in excess of 5 mSv (500 mrem).” That conservatism—and the departure from previous revisions of RG 8.39—is the decision to assume that a bystander will be 1 meter away from the patient for 24 hours a day. If the baseline threshold is used, licensees would not need to calculate patient-specific thresholds, but that could mean longer inpatient stays, greater costs to both the medical system and patients, and reduced treatment capacity.
Unrealistic baseline: The NRC’s Advisory Committee on the Medical Uses of Isotopes (ACMUI) reviewed the draft Revision 2 to RG 8.39 and submitted a final report on its review in January 2022. The ACMUI took issue with those conservative assumptions.
“The basic administered activity thresholds in Table 1, and corresponding measured dose rates in Table 2, for the release of patients (and for providing instruction) were calculated assuming an occupancy factor of 100 percent at 1 meter,” the ACMUI report reads in part. “An occupancy factor of 1.0 is unrealistic and cannot be justified for routine application, even for radionuclides with a physical half-life less than one day. The corresponding activity and dose rate values are extremely conservative, and a factor of four lower than what is currently in RG 8.39 Revision 1. This will result in an increased need for licensees to perform patient-specific dose calculations and provide patient instructions at activity levels much lower than previously required.”
The ACMUI report also asserted that “The Patient-Specific Modifying Factors and Methods presented in Appendix B, and Example Calculations illustrated in Appendix C, are overly complex and require an unrealistic level of knowledge of extended patient behavior following release.”
Yet that “unrealistic” level of knowledge is exactly what the NRC staff expects will provide a dose of realism. According to the presentation slides prepared by the NRC staff for the July 20 public meeting, “Patient specific information is used to add realism to the conservative [emphasis NRC’s] assumptions used to develop the baseline threshold values.”