Practical kidney dosimetry in peptide receptor radionuclide therapy using [177Lu]Lu-DOTATOC and [177Lu]Lu-DOTATATE with focus on uncertainty estimates

Abstract

Background Kidney dosimetry after peptide receptor radionuclide therapy using 177Lu-labelled somatostatin analogues is a procedure with multiple steps. We present the SPECT/CT-based implementation at Aarhus University Hospital and evaluate the uncertainty of the various steps in order to estimate the total uncertainty and to identify the major sources of uncertainty. Absorbed dose data from 115 treatment fractions are reported. Results The total absorbed dose with uncertainty is presented for 59 treatments with [177Lu]Lu-DOTATOC and 56 treatments with [177Lu]Lu-DOTATATE. For [177Lu]Lu-DOTATOC the mean and median specific absorbed dose (dose per injected activity) is 0.37 Gy/GBq and 0.38 Gy/GBq, respectively, while for [177Lu]Lu-DOTATATE the median and mean are 0.47 Gy/GBq and 0.46 Gy/GBq, respectively. The uncertainty of the procedure is estimated to be about 13% for a single treatment fraction, where the absorbed dose calculation is based on three SPECT/CT scans 1, 4 and 7 days post-injection, while it increases to about 19% if only a single SPECT/CT scan is performed 1 day post-injection. Conclusions The specific absorbed dose values obtained with the described procedure are comparable to those from other treatment sites for both [177Lu]Lu-DOTATOC and [177Lu]Lu-DOTATATE, but towards the lower end of the range of reported values. The estimated uncertainty is also comparable to that from other reports and judged acceptable for clinical and research use, thus proving the kidney dosimetry procedure a useful tool. The greatest reduction in uncertainty can be obtained by improved activity determination, partial volume correction and additional SPECT/CT scans.

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

“…This is in accordance with the uncertainty levels for the activity measurements of the 177 Lu solution used in the phantoms (17,18).…”

“…Notably, the absorbed dose uncertainty for WKP dosimetry was estimated to be around 5.5%. Our findings support that an optimized and calibrated SV method including multiple SVs would be useful for estimating the mean kidney absorbed dose in the time-pressed clinical workflow (17,18).…”

Active and passive dosimetry for beta-emitting radiopharmaceutical therapy agents in a custom SPECT/CT compatible phantom

“…The largest sources of uncertainty for the MC simulations were in the modeling of the experiment and determination of the source activity. An approximated uncertainty in the activity measurement of 5% was used based on a combination of manufacturer recommendations and previous publications using dose calibrators for measurements with 131 I and 177 Lu (Capintec Inc. 2010, Zimmerman and Bergeron 2016, Tiwari et al 2020, Staanum et al 2021, Van et al 2022. The type B uncertainty implicit to the EGSnrc code was assumed to be negligible compared to the dominant sources of uncertainty in the experiments.…”

Single-time-point estimation of absorbed doses in PRRT using a non-linear mixed-effects model

“…To estimate individual TIACs, individual biokinetic data of the radiopharmaceutical in the organs are required. These biokinetic data are measured by acquiring a series of images over several days using planar scintigraphy [1] , [4] , [5] or SPECT/CT [6] , [7] . Therefore, although the calculation of individual TIACs has been shown to increase the accuracy of the predicted absorbed doses [8] , [9] , individual estimation of TIACs is often not performed in the clinic due to the workload of the collection of the biokinetic data [9] .…”