Prediction of 1 cm dose-equivalent rate on the day after administration of ¹⁷⁷Lu-DOTATATE from ¹¹¹In-somatostatine receptor scintigraphy prior to treatment

When patients administered ¹⁷⁷Lu-DOTATATE are released or discharged from rooms where radiopharmaceuticals are used, the time required for release or discharge varies across patients. This study investigated whether the amount of radioactivity accumulated on ¹¹¹In-somatostatine receptor scintigraphy (¹¹¹In-SRS) performed prior to treatment can predict the 1 cm dose-equivalent rate at a distance of 1 m from the patient on the day after ¹⁷⁷Lu-DOTATATE administration.

Whole-body planar ¹¹¹In-SRS images were acquired for 21 patients. Pixel values within whole-body and abdominal (35 × 25 cm) regions of interest (ROIs) were converted to radioactivity dose (MBq). The 1 cm dose-equivalent rate (µSv/h) at a distance of 1 m from the patient 18.3 ± 0.5 h after administration of ¹⁷⁷Lu-DOTATATE was measured using an ionization survey meter.

The following relationships were observed between the radioactivity on ¹¹¹In-SRS and the 1 cm dose-equivalent rate on the day after administration of ¹⁷⁷Lu-DOTATATE: whole-body ROI: y = 0.16x + 5.01 (r = 0.56, p = 0.009), abdominal ROI: y = 0.27x + 5.13 (r = 0.63, p = 0.002). The regression equations indicate that patients cannot be released or discharged from the radiopharmaceutical room the day after ¹⁷⁷Lu-DOTATATE administration if the whole-body and abdominal ROI doses are greater than 81 and 48 MBq, respectively, on ¹¹¹In-SRS.

The amount of radioactivity accumulated on ¹¹¹In-SRS may be a predictor of release criteria for patients receiving ¹⁷⁷Lu-DOTATATE.