Inter-institutional variability in kidney dosimetry during ¹⁷⁷Lu-DOTATATE therapy in Japan

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiotherapy

Background:

• SPECT/CT imaging is crucial for personalized dosimetry in nuclear medicine, enabling tailored absorbed dose estimation and therapy optimization.
• Significant inter-institutional variability exists in dosimetry due to differences in organ contouring and calculation algorithms, necessitating standardization efforts.
• Kidney dosimetry is particularly important for therapies like 177Lu-DOTATATE, where accurate absorbed dose calculation is vital for efficacy and safety.

Purpose of the Study:

• To investigate the factors contributing to inter-institutional variability in kidney dosimetry among Japanese institutes.
• To assess the impact of organ contouring differences and calculation algorithms on kidney absorbed dose variability.
• To evaluate the effectiveness of standardized volumes of interest (VOIs) and different dosimetry software in reducing variability.

Main Methods:

• Analysis of SPECT/CT images from the 177Lu SNMMI Dosimetry Challenge involving one male and one female patient.
• Kidney volumes and absorbed doses were calculated by 10 Japanese institutes using organ-based (OLINDA 2.2, IDAC DOSE 2.1) and voxel-based (Voxel Dosimetry, RT-PHITS, MIM SurePlan MRT, OpenDose3D) software.
• Reference VOI files were distributed to evaluate the impact of contouring standardization on kidney volumes and absorbed doses.

Main Results:

• Manual kidney contouring showed substantial inter-institutional variability (up to 16.9% CV).
• Standardized reference VOIs significantly reduced volume variability (≤7.4% CV) and slightly decreased dose variability.
• Voxel-based dosimetry generally yielded higher absorbed doses than organ-based methods and demonstrated reduced inter-institutional variability, independent of contouring.
• For the female patient, kidney absorbed dose variability (%CVs) decreased from 31.36% to 6.26% (right) and 41.28% to 3.97% (left) with reference VOIs.

Conclusions:

• Significant variability in kidney volume and absorbed doses exists among Japanese institutes, impacting dosimetry reliability.
• While standardized VOIs improve volume consistency, they do not fully resolve dose differences, underscoring the importance of algorithmic approaches.
• Voxel-based dosimetry emerges as a promising method to mitigate inter-institutional variability in kidney dosimetry, irrespective of contouring variations.
• Standardization of dosimetry algorithms is crucial for ensuring accurate and reproducible 177Lu-DOTATATE kidney dosimetry in clinical practice.