Estimation of Absorbed Doses of Indigenously Produced "Direct-route" Lutetium-177-[177Lu]Lu-DOTA-TATE PRRT in Normal Organs and Tumor Lesions in Patients of Metastatic Neuroendocrine Tumors: Comparison with No-Carrier-Added [177Lu]Lu-DOTA-TATE and the Trend with Multiple Cycles.

Abstract

Background: Lutetium-177-labeled somatostatin analogue, [177Lu]Lu-DOTA-TATE is most commonly used across the world for peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs). The primary objective of this study was to estimate the absorbed doses in organs and tumor lesions in NET patients treated with indigenously produced "direct-route" [177Lu]Lu-labeled DOTA-TATE and impact of multiple treatment cycles on absorbed doses, and compare with those treated with no-carrier-added [177Lu]Lu-labeled DOTA-TATE. Materials and Methods: Sixty patients of NET were enrolled in this prospective study. These patients received up to 6 cycles of PRRT with [177Lu]Lu-DOTA-TATE (total 232 cycles) at 10- to 12-week intervals between the two successive therapy cycles. The patients were administered 5.55-7.4 GBq (150-200 mCi) of [177Lu]Lu-DOTA-TATE in 100 mL of normal saline over a period of 30 min. Postadministration whole-body planar scintigraphy were acquired at five time points 0.5 (prevoid), 2, 12, 24, and 72 h (postvoid) and one SPECT scan at 24 h (postvoid). Number of disintegrations was determined from time-activity curves generated by drawing regions of interests (ROIs) on the images. Tumor masses were derived from computed tomography (CT) data. The absorbed doses for normal organs and tumor lesions were calculated using OLINDA 2.1.1 software. The same were also estimated in a group of 22 patients who were treated with no-carrier-added [177Lu]Lu-labeled DOTA-TATE. Results: The mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.64 ± 0.21, liver 0.10 ± 0.05, spleen 0.88 ± 0.35, bone marrow 0.04 ± 0.02, urinary bladder 0.26 ± 0.06, heart wall 0.04 ± 0.02, and whole-body 0.06 ± 0.02. Tumor dosimetry was performed in a total of 410 tumor lesions, the mean absorbed dose to the tumor lesions was 4.79 ± 4.23 Gy/GBq. Large variations were observed in absorbed doses received by these lesions (range: 0.15-21.26 Gy/GBq). With no-carrier-added [177Lu]Lu-DOTA-TATE, the mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.76 ± 0.16, liver 0.10 ± 0.05, spleen 1.14 ± 0.31, bone marrow 0.05 ± 0.02, urinary bladder 0.27 ± 0.05, heart wall 0.06 ± 0.02, whole-body 0.07 ± 0.02, and tumor dose 5.87 ± 5.74. Conclusions: There was no statistically significant difference in the dosimetry data of patients treated with no-carrier-added (indirect route) [177Lu]Lu-labeled DOTA-TATE and the dosimetry data of patients treated with [177Lu]Lu-labeled with DOTA-TATE formulated using 177Lu produced through "Direct-route" and were comparable with the data reported.