Evaluation of Using Small Volume of Interest Regions for Clinical Kidney Dosimetry in 177Lu-DOTATATE Treatments

Abstract

Introduction: A small volume of interest (SV) method has been proposed and used to obtain time-effective kidney dosimetry protocols for 177Lu-DOTATATE treatments. However, SV methods show only modest precision and accuracy compared to the whole-kidney parenchyma (WKP) segmentation approach. Here we aim to evaluate the influence of patient-specific partial volume effect corrections on kidney dosimetry calculations based on the WKP method, to perform a comparative analysis between the WKP and SV methods, and to determine how the use of multiple SVs affected the accuracy of clinical kidney dosimetry. Methods: We obtained SPECT/CT of 18 patients at 24, 48, and 168 hours after injection of 177Lu-DOTATATE (7.3–7.8 GBq). The SPECTs were corrected for attenuation, scatter, and collimator detector response with Monte Carlo-based OSEM reconstruction (ASCC-SPECT) and post-filtered with a 0- to 12-mm Gaussian filter, or were only attenuation corrected with a Hann post-filter (AC-SPECT) as described in the first application of the SV method. Kidney dosimetry based on the manually segmented WKP was used as the golden standard. Recovery coefficients (RCs) for each WKP were determined by Monte Carlo simulations, and RCs for SVs were determined relative to the WKP method. Kidney absorbed doses were estimated based on measured activity concentrations fitted using the mono-exponential function. Uncertainties were measured for kidney dosimetry calculated based on the SV method with 1–5 VOIs with sizes of 4 mL (SV4), 2 mL (SV2), and 0.6 mL (SV0.6). Results: The mean RCs of the WKP volumes (31–243 mL) in non-filtered ASCC-SPECT and AC-SPECT were 0.85 (0.73–0.90) and 0.62 (0.46–0.51), respectively. The uncertainty in the kidney dosimetry calculation based on one SV4 on each SPECT data-point was 10.4%, and decreased as the number of VOIs was increased from 1 to 5. With the SV2 method, using a mean of 5 VOIs per kidney parenchyma, the uncertainty decreased to 6.3%. The uncertainty of the WKP method was 5.5%. Conclusion: Kidney dosimetry based on RC-corrected multiple SVs located on representative uptake regions in the kidney parenchyma is a fast approach that can provide satisfactory accuracy as compared to a single SV method.