# Toward the standardization of radiopharmaceutical therapies: a technical note evaluating a clinical dosimetry workflow for single-time-point 177Lu SPECT/CT-based therapies

## TL;DR

This study evaluates a workflow for calculating radiation doses in Lu-177 therapies to improve standardization and accuracy.

## Contribution

The study proposes a harmonized dosimetry workflow for single-time-point Lu-177 SPECT/CT therapies.

## Key findings

- The voxel-based VSV method showed higher absorbed doses than the LD method by 10 to 150%.
- The overall variability in absorbed dose reached up to 84% when different methods were used.
- The DC kernel was found viable for creating reference absorbed doses.

## Abstract

The lack of standardized dosimetry workflows in lutetium-177 (\documentclass[12pt]{minimal}
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\begin{document}$$^{177}$$\end{document}177Lu) radiopharmaceutical therapies results in inconsistent absorbed doses and limits treatment planning. This study aims to evaluate the accuracy and variability of a single-time-point 177Lu SPECT/CT commercial workflow to help harmonize its protocol.

The dosimetry workflow evaluated in this study predominatly followed that of MIM SurePlanTM MRT. 177Lu SPECT/CT images of a Jaszczak and a NEMA phantoms were acquired in GE 670 DR scanner. Absorbed dose (Gy/MBq/s) was calculated in the background and sphere inserts with varied reconstruction iterations, calibrations, voxel-based dosimetry methods, and target volume segmentations. Ground truth absorbed doses were created using CT images and voxel S-value (VSV) water kernels. The validity of the density-corrected (DC) kernel for use in ground-truth dosimetry evaluations was further investigated. The accuracy and variability of the dosimetry workflow were evaluated using percent error and the coefficient of variation (CV) of mean absorbed doses.

Mean absorbed dose accuracy improved for both the voxel-based VSV and local deposition (LD) methods until 480 equivalent iterations for all target volumes. DC kernel was found viable for creating reference absorbed doses. The calibration CV was 5.18% when phantom and calibration regions were varied. The VSV method demonstrated absorbed doses that were 10 to 150% higher than those calculated with the LD method. The overall variability in absorbed dose reached up to 84% when reconstruction, calibration, dosimetry, and segmentation methods were varied.

A single dosimetry workflow has demonstrated markedly large variability in absorbed dose accuracy. By evaluating the accuracy of absorbed dose, our study helped to propose a harmonized MIM SurePlanTM MRT workflow for single-time-point \documentclass[12pt]{minimal}
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\begin{document}$$^{177}$$\end{document}177Lu SPECT/CT-based therapies.