EANM recommendations for dosimetry in targeted radionuclide therapy with alpha-emitters

Dosimetry can be a useful tool for personalisation of targeted radionuclide therapy (TRT) procedures and for increasing knowledge of the therapies, enabling the continuous development of theragnostic concepts. While only one alpha-emitting radiopharmaceutical, [ 223 Ra]Ra-Cl 2 , is currently authorised for clinical use, this is expected to change in the coming years, as there is a continuous increase in research activities and clinical trials with alpha-emitting radiopharmaceuticals, covering a broad range of diseases such as prostate cancer, breast cancer and neuroendocrine tumours. This document addresses key challenges such as activity quantification at low count rates, daughter redistribution, relative biological effectiveness, small-scale dosimetry and microdosimetry, in order to provide robust recommendations for dosimetry in TRT with alpha-emitters. It includes an overview of the physical characteristics of the main alpha-emitting radionuclides used in TRT, followed by a review of the present status for activity quantification and absorbed dose calculation. Reported main dosimetry data for TRTs that include alpha emitters until the writing of the document are also summarised. Lastly, the document provides general recommendations for dosimetry of TRTs that include alpha emitters, based on literature review and expert opinion. Given the plethora of emerging treatments with various carriers, distribution patterns and radionuclides; it is emphasized that careful consideration of potential pitfalls and robust reporting are needed. Suggestions for uncertainty reporting are hence also included. The purpose of these recommendations is to encourage, both in clinical trials and clinical routine, the practice of patient-specific dosimetry in TRT with alpha emitters, which can provide valuable information for progressing the treatments.