¹⁷⁷Lu-labelled compounds show many advantages for dosimetry assessments due to the attractive physical properties of the isotope which comprise a clearly separated gamma peak at 208 keV and low abundance of photons which permits reliable quantitative imaging after therapy. In addition, the low range of beta particles is advantageous for radiation protection.

This talk mainly focuses on dosimetry methodology which includes consideration of the number and time points of scans, quantitative imaging, methods for integrating time-activity curves and calculating absorbed doses. The most recent results of absorbed dose calculations for the kidneys, bone marrow, and tumors will be presented. Reasons are given why the absorbed doses reported for radiopeptide therapies using ¹⁷⁷Lu labelled compounds taken from clinical studies show a high variability.

For radiopeptide therapies with ¹⁷⁷Lu labelled compounds the widely assumed dose-limit to the kidneys is 23-25 Gy. This value is based on data from external beam therapy; a dose-response for kidney toxicity after ¹⁷⁷Lu radiopeptide therapies has not been observed. Therefore, further clinical studies are suggested to establish such a dose-limit for kidney toxicity. The results of such studies might lead to further optimization of treatments with ¹⁷⁷Lu labelled compounds. In addition, new studies which link DNA damage to internal dosimetry will be presented as this might bring new insights in the individual patients’ radiation sensitivity associated with PRRT therapy.