MSOR11 Presentation Time: 5:50 PM

Lu177 PSMA and Lu177 DOTATATE are radiopharmaceutical therapies delivered in outpatient settings with fixed activity treatments. A proposed regulatory rule change (NRC-2023-0086) lowers patient release criteria from approximately 8.6 mR/h to 2.2 mR/h for Lu177. Decreasing tumor to kidney absorbed dose with subsequent cycles has been observed for both therapies; consequently the first cycle may be the optimal time to escalate activity. We aim to identify potential compliance issues for standard fixed activity treatments and in the context of dose escalation. We conducted an IRB-approved retrospective chart review of all Lu177 PSMA and DOTATATE treatments in our department for the calendar year 2023. Release exposure rate measurements were obtained within approximately 10 minutes following completion of Lu177 DOTATATE infusion or Lu177 PSMA syringe injection. The exposure rate measurements were evaluated for compliance with the proposed NRC rule change. To estimate the amount of dose escalation possible in a cycle while satisfying release regulations, we scaled the current prescribed activity by the ratio of the release criteria to the patient's current exposure rate measurement. A total of 211 (62 patients) Lu177 PSMA injections were administered. The nominal prescribed activity was < 7.4 GBq in 30/211 treatments. Lu177 DOTATATE was infused 96 times (36 patients), and the nominal prescribed activity was 7.4 GBq for all treatments. For Lu177 PSMA, post-injection patient exposure rates were 1.78 ± 0.31 mR/h (0.26 to 3.2) (average ± stdev (min to max)), with 9 out of 211 measurements not meeting proposed release rule changes. For Lu177 DOTATATE, post-infusion patient exposure rates were 2.07 ± 0.28 mR/h (1.38 to 3.0) and 23/96 did not satisfy the proposed rule change. For DOTATATE the average activity escalation possible is 8% ± 15% (-27% to 60%) and 323% ± 60% (187% to 523%) for the proposed rule and current rule, respectively. For PSMA patients prescribed 7.4 GBq, the average activity escalation possible is 23% ± 19% (-31% to 86%) and 379% ± 73% (169% to 629%) for the proposed rule and current rule, respectively. Both Lu177 DOTATATE and Lu177 PSMA are currently impacted by the proposed patient release rule change when administering a nominal prescribed activity of 7.4 GBq. The proposed rule change will further limit activity escalation in a single cycle without modifications to clinical workflows. Additional holding of patients and encouraging bladder voiding may be necessary to satisfy the proposed rule change for all cases.