Validation of Simplified Renal Dosimetry Protocols for ¹⁷⁷Lu-DOTATATE Therapy Using the IDAC-dose Software

The multi-time-point imaging method for renal dosimetry in lutetium-177 (¹⁷⁷Lu)-DOTATATE therapy imposes a significant burden. This study aimed to validate simplified two-time-point (2TP) and three-time-point (3TP) protocols using the International Commission on Radiological Protection-compliant IDAC-Dose 2.1 software.

This retrospective study analyzed 28 kidneys obtained from 17 patients with neuroendocrine neoplasms. Renal absorbed doses from a reference four-time-point (4TP) schedule (4, 24, 72, and 120 hours) were compared with ten simplified protocols using statistical analyses of error and agreement.

Protocols that included the 120-hour time point demonstrated significantly higher accuracy. The 2TP (4, 24) protocol showed a profound underestimation [mean percentage error (MPE): -14.3%] and a high error. In contrast, the 2TP (24, 120) protocol showed excellent agreement [MPE: 0.57%, mean absolute percent error (MAPE): 5.5%]. Among 3TP methods, the 3TP (24, 72, 120) protocol yielded the highest accuracy (MAPE: 1.97%).

Accurate renal dosimetry in ¹⁷⁷Lu-DOTATATE therapy can be achieved with simplified protocols. Incorporating a late-phase time point (around 120 hours) is essential for reliable estimation. The 2TP (24, 120) and 3TP (24, 72, 120) combinations are suggested as feasible alternatives to the standard 4TP method.