Assessment of environmental radioactive contamination in radiation therapy rooms: comparison between therapy after Lu-177 DOTATATE and I-131.

OBJECTIVE: This study investigated the actual state of remnant radioactive contamination in hospital rooms after Lu-177 DOTATATE radioisotope therapy for neuroendocrine tumors and compared it with that after I-131 radioisotope therapy for thyroid cancer. Furthermore, we aimed to obtain basic data to consider the appropriateness of the restrictions in Japan. METHODS: In this study, 20 rooms for Lu-177 DOTATATE radioisotope therapy and 31 rooms for I-131 radioisotope therapy treated between April 2024 and April 2025 were evaluated. The ambient radiation level was monitored; surface contamination was measured using a GM surface contamination monitor; and removable surface contamination was quantified. RESULTS: The remnant contamination of the radioisotope therapy room after treatment with Lu-177 DOTATATE was significantly lower than that after treatment with I-131 after patient discharge. For Lu-177 DOTATATE, a high ambient dose was observed only at the bedside and shower room, and high surface contamination was only found in the toilet bowl. CONCLUSIONS: The remnant ambient dose/contamination in the room after Lu-177 DOTATATE therapy was limited compared with that after I-131 therapy. We believe that the findings of this study will guide the development of more proper and suitable strategies for managing Lu-177 DOTATATE therapy.