Safety data collection for clinical translation

Deliverable D4.3 Safety data collection for clinical translation This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101008571 (PRISMAP). This document reflects only the view of the author(s). The Agency is not responsible for any use that may be made of the information it contains. Deliverable D4.3 ii Project Acronym PRISMAP Project Title The European medical isotope programme: Production of high purity isotopes by mass separation Grant Agreement No. 101008571 Topic INFRAIA-02-2020: Integrating Activities for Starting Communities Project start date 01 May 2021 Nature Report Dissemination level Public Due date M53 Date of delivery M53 Lead partner MUI Contributing partners ARRONAX, CHUV, DTU, CERN, ILL, IST-ID, JRC, KULeuven, NCBJ, PSI, SCK CEN, TUM Authors Clemens Decristoforo, Hessam Roustaei Firouzabad (MUI); Kristof Baete (KULeuven), Calogero D'Alessandria (TUM); Renata Mikolajczak, Malgorzata Zoltowska (NCBJ); Zeynep Talip, Nick van der Meulen (PSI); Thierry Stora (CERN); Claire Deville, Mikael Jensen (DTU); Ulli Köster (ILL); Lurdes Gano (ISTID); Frank Bruchertseifer (JRC); Maarten Ooms, Michiel Van de Voorde (SCK CEN) Reviewers Sarah Baatout (SCK-CEN), Maija Radzina (LU) Point of Contact Clemens Decristoforo Institution MUI E-mail [email protected] Phone +4351250480951 © PRISMAP 2021. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Deliverable D4.3 iii Revision History Version Date Author Comment 0.1 18.01.2025 C. Decristoforo Table of Contents 0.2 24.02.2025 C. Decristoforo First draft 0.3 02.06.2025 K.Baete Input NMES study 0.4 11.08.2025 H. Roustaei Firouzabad, C. Decristoforo Safety data Tb-161 and Ac-225 For review WP4 0.5 28.08.2025 K. Baete, R. Mikolajczak, M. Van der Voorde, C. D`Alessandria Comments from WP4 implemented, for internal PRISMAP review 0.6 07.09.2025 M. Radzina Review 0.7 23.09.2025 S. Baatout Review 0.9 26.09.2025 V. Gobry, K. Leufgen Review and final formatting, version for review and approval by the general assembly 1.0 29.09.2025 K. Leufgen Final version, approved by the general assembly Deliverable D4.3 iv Contents Abbreviations, Participant short names vi Abbreviations vi Participant short names vii List of Figures viii List of Tables viii Summary 1 1. Introduction 1 1.1 Standardisation and harmonisation of Safety Data within PRISMAP and Scope of deliverable 4.3 1 1.2 Deviations from original plan 1 2. General Activities related to the Safety aspects of Novel radionuclides 2 2.1 The EMA guideline on antibody-based radiopharmaceuticals and its concept paper for revision 2 2.2 The EMA concept paper on the clinical development of therapeutic radiopharmaceuticals and novel radionuclides 3 2.2.1 EMA concept paper 3 2.2.2 PRISMAP response 3 3. The Terbium-161 Nuclear Medicine Equipment Standardisation (NMES) Study 3 3.1 Description and aim 3 3.2 Methods and activities 4 3.2.1 Preparations 4 3.2.2 Activity meter calibration 5 3.2.3 Emission tomography imaging devices 7 3.2.4 Gamma counting analysis 8 3.3 Outcome and summary 9 4. Safety Data of specific radionuclides from PRISMAPs portfolio 9 4.1 Terbium – 161 9 4.1.1 Preclinical safety data 9 4.1.2 Clinical safety data 10 4.2 Actinium-225 11 4.2.1 Clinical safety data 12 5. Conclusions 14 References 14 Annexes 18 Deliverable D4.3 v Annex 1: Comments on EMA Concept paper on the revision of the Guideline on Radiopharmaceuticals Based on Monoclonal Antibodies (general comments) 18 Annex 2: Comments on EMA Concept paper on clinical evaluation of therapeutic radiopharmaceuticals in Oncology (general comments) 19 Annex 3: Publication on the Clinical Safety Data of Actinium-225 (Title Page, submitted for publication, available at: https://zenodo.org/records/16986225 22 Deliverable D4.3 vi Abbreviations, Participant short names Abbreviations BWP Biologics Working Party (of EMA) CA Consortium Agreement CT Computer Tomography BWP Biologics Working Party (of EMA) DoA Description of Action EANM European Association of Nuclear Medicine EDQM European Directorate for the Quality of Medicines EDTA Ethylenediamine Tetraacetic Acid, a universal metal chelator EMA European Medicines Agency EU European Union GA Grant Agreement GMP Good Manufacturing Practices GEP-NET Gastroenteropancreatic Neuroendocrine Tumor IAEA International Atomic Energy Agency IMPD Investigational Medicinal Product Dossier LEHR low-energy high-resolution (collimators) MAuth mCRPC Marketing Authorisation metastatic Castration-Resistant Prostate Cancer MELP medium-energy low-penetration (collimators) NEMA National Electrical Manufacturers Association NMES Nuclear Medicine Equipment Standardisation NMI National Metrology Institute SCLC Small Cell Lung Cancer Pharm Eur European Pharmacopoeia PET positron emission tomography QA Quality Assurance QC Quality Control SAE Serious Adverse Event ()SPECT (micro, for small animal) single photon emission computed tomography SOP Standard Operating Procedure SSTR Somstostatin Receptor TEAEs TRT Treatment-emergent Adverse Events Targeted Radionuclide Therapy tRPs Therapeutic radiopharmaceuticals Deliverable D4.3 vii Participant short names CERN European organisation for nuclear research NPL National Physical Laboratory PSI Paul Scherrer Institut CEA Commissariat à l’énergie atomique et aux énergies alternatives IST-ID Associação do Instituto Superior Técnico para a IST-ID Investigação e Desenvolvimento DTU Danmarks Tekniske Universitet CHUV Centre hospitalier universitaire vaudois GANIL Grand Accélérateur National d’Ions Lourds SCK CEN Studiecentrum voor Kernenergie / Centre d'étude de l'énergie nucléaire ARRONAX Groupement d’intérêt public ARRONAX ESS European Spallation Source ERIC TUM Klinikum rechts der Isar der technischen Universität München KULeuven Katholieke Universiteit Leuven MedAustron Entwicklungsund Betriebsgesellschaft MedAustron GmbH SCIPROM SCIPROM Sàrl MUI Medizinische Universität Innsbruck ILL Institut Max von Laue - Paul Langevin JRC JRC -Joint Research CentreEuropean Commission NCBJ Narodowe Centrum Badań Jądrowych GSI GSI Helmholtzzentrum fr Schwerionenforschung GmbH LU Latvijas Universitāte INFN Istituto Nazionale di Fisica Nucleare UiO Universitetet i Oslo Deliverable D4.3 viii List of Figures Figure 1: Different types of Activity meters used in the NMES study 6 Figure 2: A dual-head Symbia Intevo Bold SPECT/CT (Siemens) measuring a phantom as used in the NMES study 8 List of Tables Table 1. Current studies reporting human application of Tb-161 radiopharmaceuticals and related safety reports 10 Table 2. Published relevant safety data from studies utilising Ac-225 radiopharmaceuticals 12 Table 3. Registered trials retrieved from ClinicalTrials.gov database involving Ac-225 (Data included until August 2025) 13 Summary This document presents a summary of PRISMAP Work Package 4 (WP4) activities on standardisation and harmonisation with a focus on safety data supporting the clinical translation of novel radionuclides from the PRISMAP portfolio. Regulatory developments relevant to radiopharmaceuticals were systematically monitored, and formal responses were submitted to the European Medicines Agency (EMA) to ensure that the specific requirements for developing and clinically translating radiopharmaceuticals incorporating novel radionuclides are appropriately addressed. Of particular significance is the ongoing development of an EMA guideline on the clinical development of therapeutic radiopharmaceuticals, which is expected to have a substantial impact on the field and should remain a priority for future engagement. A dedicated Nuclear Medicine Equipment Standardisation (NMES) study on terbium-161 (Tb-161) was undertaken to strengthen the safety profile for both preclinical and clinical applications of existing and emerging radionuclides. This study assessed practical and technical aspects of Tb-161 activity determination using preclinical and clinical equipment in hospital settings, with emphasis on activity meters, emission tomography devices, and gamma counting systems. Conducted collaboratively by PRISMAP partners SCK CEN, KULeuven, and NPL, the NMES highlighted the critical importance of rigorous standardisation procedures for nuclear medicine instrumentation, particularly in the context of novel therapeutic radionuclides. The findings underscore the necessity of sustained investment in metrological and procedural harmonisation as radionuclide-based therapies become increasingly central to precision oncology. In addition, dedicated safety datasets for two clinically advanced PRISMAP radionuclides—Tb-161 and actinium-225 (Ac-225)—were compiled. For Tb-161, recent preclinical safety data, with a focus on comparisons to the established Lu-177 standard, were reviewed alongside available clinical safety information. For Ac-225, safety data from 39 clinical studies were collected and assessed. Across these datasets, both radionuclides demonstrated favourable safety profiles for their intended oncological applications. These results provide an evidence base for developing the benefit–risk analyses required in Investigational Medicinal Product Dossiers (IMPDs), facilitating the clinical translation of additional novel radiopharmaceuticals. 1. Introduction 1.1 Standardisation and harmonisation of Safety Data within PRISMAP and Scope of deliverable 4.3 In this WP, it was intended to collect harmonised and standardised data related to non-clinical and clinical safety aspects of radiopharmaceuticals required for submission of IMPD for competent authorities. We focused here on three aspects. First, ongoing developments in the pharmaceutical regulatory field related to pharmaceutical safety aspects required actions from WP4 within PRISMAP to ensure that novel radionuclides and developments from those are considered. Further, a dedicated NMES study was initiated with the example of Tb-161 with the intention to contribute to the improvement of the safety profile for the preclinical and clinical use of existing and novel radionuclides, and all associated radiopharmaceuticals. It focused on the standardisation of activity meters, emission tomography devices, and gamma counting equipment used in universities and hospitals for preclinical development and clinical trials. Finally, a collection of clinical and non-clinical safety data for two clinically advanced radionuclides from PRISMAP`s portfolio, Tb-161 and Ac-225 was performed and included in this document to support users in developing the required documentation within Investigational Medicinal Product Dossiers for clinical translation. 1.2 Deviations from original plan WP4 aims at the standardisation and harmonisation of PRISMAP`s novel radionuclides within the process of clinical translation, especially focusing on the pharmaceutical regulatory framework in Europe. This regulatory landscape and the challenges have been extensively discussed in WP4 activities such as a Deliverable D4.3 8 Figure 2: A dual-head Symbia Intevo Bold SPECT/CT (Siemens) measuring a phantom as used in the NMES study For this study, we used a dual-head Symbia Intevo Bold SPECT/CT (Siemens). A set of detector energy windows was defined for Tb-161. Using a small point source, we tuned the energy windows of the intrinsic detector and assessed its performance by measuring the intrinsic detector uniformity for Tb-161. A cylindrical water phantom was filled with a traceable amount of Tb-161 activity, which was uniformly dissolved in the water. For about one month multiple SPECT/CT acquisitions of the phantom were performed over an activity range of around 1.5 GBq down to 120 MBq using low-energy high-resolution (LEHR) and medium-energy lowpenetration (MELP) collimators. For each SPECT acquisition, a system volume sensitivity factor (cps/MBq) was determined. In addition, the spheres of a NEMA image quality phantom were filled with a traceable activity concentration, and SPECT/CT imaging was performed to assess recovery coefficients for the acquisition and a variety of reconstruction parameters. The primary goal of the SPECT/CT standardisation was to compare the results obtained in this NMES study with those of some recent publications [6,9]. A similar approach was used for the standardisation of a µSPECT system. We used a γ-CUBE (Molecubes®) for which Tb-161 energy window settings were defined and tuned, and a detector normalisation was performed using a small point source. Quantitative calibration of the system was performed using traceable amounts of Tb-161 activity that were put into a 10 ml and a 20 ml syringe, comparable to a uniform phantom in clinical SPECT systems. Subsequent µSPECT images of the syringes were used to determine system calibration factors for acquisition and reconstruction settings. 3.2.4 Gamma counting analysis A gamma counter is a very useful instrument that can assist and support in the standardisation of equipment. This device can measure the amount of radioactivity in samples by detecting the radionuclide gamma and Xray emissions within a certain energy range. In principle, it should be straightforward to determine a calibration factor for the radionuclide, the standardised source geometry, and specific gamma counter settings, such as the energy window. Once calibrated, a gamma counter can then be used to compare the observed and the expected activity in samples along the standardisation process. In this study, we used a gamma counter for the measurement of a variety of samples that were extracted from radioactive solutions in vials, syringes and imaging phantoms at different steps of the overall standardisation workflow. This approach was meant to add a level of QC to the various calibration and verification procedures. The response of the gamma counter in cpm/Bq was compared with the expected activity of the sample, and the activity of each sample was determined by the net weight of the sample and the expected activity concentration in the container from which the sample was collected. At a specific time, the samples in this study contained a variety of activity concentrations. This is due to the dilution of activity for the creation of secondary geometries with activity meters and imaging phantoms. It was found to be very important to first perform an analysis of the gamma counter response over a wide Deliverable D4.3 9 range of activities, which is the linearity of the gamma counter for a certain radionuclide. At high activity, the response of the gamma counter becomes nonlinear, mainly due to dead time effects. At low activity, the influences of background and noise become important. In between, there is a region of linear response of the measuring device. Capturing such a gamma counter response curve can aid in the standardisation process. In some steps of the equipment standardisation, it is impossible to determine the activity or activity concentration of a sample or phantom with the geometry requirements for an activity meter. Sometimes the activity can simply be too low for a reliable measurement using an ionisation chamber. In that case, a gamma counter is a more appropriate and reliable tool, and so it must be taken into account for the NMES. We studied the gamma counter response curve for Tb-161 in this NMES study and were able to use this curve for the verification of the activity in all of the recipients and phantoms that were used along the calibration workflow. After many weeks of repeatedly measuring samples, we noticed the presence of Tb-160 in the gamma ray spectra. Unavoidably, small quantities of Tb-160 are created as an impurity during the production of Tb-161 [10,11]. Eventually, Tb-160 appears in the gamma counter measurements after many weeks of decay, and it can influence the response curve significantly at low Tb-161 activity levels. Hence, it is important to take the possible occurrence of impurities into account during the calibration and verification process. 3.3 Outcome and summary The NMES study conducted within the PRISMAP framework has demonstrated the critical importance of rigorous standardisation procedures for nuclear medicine equipment, particularly in the context of emerging radionuclides like Tb-161. Through a comprehensive approach involving activity meter calibration, emission tomography imaging, and gamma counting analysis, this study has highlighted both the technical challenges and practical solutions necessary to ensure accurate, traceable, and reproducible measurements. The collaborative efforts between clinical, preclinical, and metrology institutions have not only enhanced the reliability of quantitative imaging and dosimetry but also contributed to the broader goal of improving safety and efficacy in theranostics applications. These findings underscore the need for continued investment in standardisation protocols as radionuclide therapy becomes increasingly central to precision oncology [12]. 4. Safety Data of specific radionuclides from PRISMAPs portfolio 4.1 Terbium – 161 Within PRISMAP, Tb-161 has been among the radionuclides that have been most widely applied for out of the whole portfolio offered within the project. Even though no clinical trial resulted from this interest within PRISMAP, a PRISMAP user group applied for an IMPD to enter into a clinical phase, several other clinical applications have been reported recently, and several publications were dedicated specifically to non-clinical and clinical safety aspects of Tb-161 used for therapeutic applications. These data are summarised and presented herein. 4.1.1 Preclinical safety data An important question in using Tb-161 clinically is whether it can be assured that 161Tb-radiopharmaceuticals show the same biological properties as compared to their Lu-177 labelled counterparts, and whether preclinical and clinical data from Lu-177 studies can be used to support safety assessment. Several studies showed in parallel studies a comparable biological behaviour of Lu-177 and Tb-161 labelled radiopharmaceuticals for different applications [13–16], however, a simultaneous, direct comparison of both radiolanthanides was missing. Recently, Walimann et al [17] studied the similarities and differences of four (radio)lanthanides (Lu, Tb, Gd, Eu) simultaneously applied as complexes of biomolecules or in ionic form, both in vitro and in vivo tumour models. Whereas all lanthanide complexes (both PSMA ligands and Somatostatin analogues) did not reveal any differences in cell studies nor tumour models, the free lanthanide Deliverable D4.3 10 salts revealed differences with higher bone accumulation of lutetium salts as compared to terbium counterparts. This was also confirmed with dual-isotope SPECT/CT imaging. These data confirm that Lu-177 can be replaced by Tb-161 without affecting the tissue distribution profile of the resultant radiopharmaceuticals. Another concern of using Tb-161 is whether the higher absorbed dose of Tb-161 impairs the tolerability of Tb-161 radiopharmaceuticals as compared to their Lu-177 counterparts. In particular, the bone marrow toxicity is a particular potential risk. To address this concern, a recent study from PSI [18] by preclinical comparison of the tolerability of Tb-161and Lu-177-based Somatostatin receptor (SSTR) binding DOTA-LM3 and DOTATATE in immunocompetent mice applying 20-100MBq of these radiopharmaceuticals labelled with both radionuclides. They looked into treatment-related effects on blood cell counts and assessed bone marrow smears, blood plasma parameters and organ histology at the end of the study. They found hematologic changes were more pronounced for the SSTR-antagonist DOTA-LM3 than the agonist DOTATATE, which corresponds to its higher treatment efficiency [15]. However, despite the increased absorbed dose delivered by Tb-161 over Lu-177, no difference in haematological toxicity, renal and hepatic functions was observed. This supports the concept of using comparable activities of Tb-161 in clinical studies as those applied for Lu-177. However, certainly more data are needed to substantiate such findings for different radiopharmaceuticals and applications and cannot replace dose finding studies in clinical trials. 4.1.2 Clinical safety data Table 1. Current studies reporting human application of Tb-161 radiopharmaceuticals and related safety reports Study Year Ref Radiopharmaceutical No of patients Type of study Max. Total activites adminsitered Reported Adverse events Baum et al 2021 [19] DOTATOC (SSTR) 1 Compassionate Use, retrospective < 2GBq None AlIbraheem et al 2024 [20] PSMA 4 Compassionate Use, retrospective 1 x 5,5GBq Fatigue (n=2), creatinine increase (n=1) Abdlkadir et al 2024 [21] PSMA 1 Compassionate Use, retrospective 1 x 5,5GBq None Chirindel et al 2024 [22] SibuDAB (PSMA) 1 Prospective Phase I/II 1x 1GBq None Fricke et al 2024 [23] DOTA-LM3 (SSTR) 1 Prospective Phase I/II 1x1GBq None SchaeferSchuler et al 2024 [24] PSMA 617 6 Compassionate Use/ Prospective Registry 1 x 6.4GBq Anemia, leukopenia, thromocytop enia (n=1), xerostomia (n=2) Buteau et al 2025 [25] [26] PSMA I&T 30 Prospective Phase I/II 4.4-7.4 up to 6x Grade 3: Pain (n=1) Lymphopenia [n=1] Jacobs et al 2025 [27] DOTATATE (SSTR) 1 Compassionate Use, retrospective 5.7 None Published data (not including conference abstracts) on the use of Tb-161, including some safety data, are still scarce to this date. Table 1 summarises data from 8 publications found in the public domain (July 2025). In Deliverable D4.3 11 total application of Tb-161 radiopharmaceuticals was reported in 45 patients. The very first report on the human application of Tb-161 was published in 2021 using [161Tb]Tb-DOTATOC, including first biodistribution data and dosimetry and reported no related side effects in two cycles with a total of less than 2GBq administered. Since 2025, 4 additional anecdotal, retrospective compassionate use case studies were published, including 12 patients, 11 using PSMA ligands and one with DOTATATE. Al-Ibraheem et al reported fatigue in 2 and creatinine increase in 1 of 4 patients after application of a Tb-161 labelled PSMA ligand. In another compassionate use study with [161Tb]Tb-PSMA 617 in 6 patients with a single administration of 6.4GBq (mean) in one patient, anaemia, thrombocytopenia and leukopenia were reported [24], which was considered to be disease-related and in 2 patients pre-treated with Ac-225 ligands, xerostomia was found. Other reports were just single case studies, two of them just dosimetry studies, with no safety-related data mentioned [21–23,27] and included both SSTR and PSMA ligands. The most extensive report on the safety of Tb-161 in humans can be found in the outcome of the VIOLET study, a single-centre, single-arm, prospective Phase I/II study with [161Tb]Tb-PSMA I&T in 30 prostate cancer patients [26]. Up to 6x 7.4GBq Tb-161 was administered without observation of a dose-limiting toxicity. The most frequently observed treatment-emergent adverse events (TEAEs) attributed to therapy were predominantly grade 1 in severity. These included xerostomia in 21 patients (70%, all grade 1), anaemia in 16 patients (53% grade 1) and in an additional four patients (13%) as grade 2, asthenia/fatigue in 12 patients (40% grade 1) and one patient (3%) as grade 2, and nausea in seven patients (23%, all grade 1). Other reported TEAEs comprised pain in three patients (10% grade 1) and one patient (3%) with grade 3 intensity, thrombocytopenia in six patients (20%, all grade 1), and lymphopenia in eight patients (27% grade 1), ten patients (33% grade 2), and one patient (3%) as grade 3 (refer to Table 2). A single patient (3%) experienced a treatment-related serious adverse event (SAE), manifesting as grade 3 pain within 48 hours post-administration of the initial treatment cycle. Notably, there were no grade 4 TEAEs or treatment-related fatalities. No dose modifications or treatment discontinuations due to toxicity were required during the study. In summary, these data show a very acceptable safety profile of Tb-161 in a larger patient cohort, even with high activities of Tb-161 being administered. These data are related to a single radiopharmaceutical, and for all reported studies, long-term observations are missing. It is expected that the dataset on the clinical safety of Tb-161 radiopharmaceuticals will be expanded very soon with more outcomes reported on ongoing prospective clinical trials. 4.2 Actinium-225 A growing strategy in precision oncology is targeted radionuclide therapy. Given their distinct radiophysical and radiochemical characteristics, alpha-emitters are the radioisotopes that are receiving increasing attention for TRT (28). Actinium-225 (Ac-225) is an alpha-emitting radionuclide that is considered a "nanogenerator" of alpha particles. It has a half-life of 9.92 days, which is long enough to transport the radionuclide from production sites to clinics. During its decay to stable bismuth-209 (Bi-209), Ac-225 produces a total of four net alpha particles, maximising its therapeutic potential, which makes it a highly potent alpha emitter [29]. It can be efficiently chelated with radioligands for targeted delivery owing to its radiochemical characteristics, which are comparable to those of trivalent metals and lanthanides [30]. Ac-225 has shown therapeutic efficacy in clinical trials, especially for metastatic castration-resistant prostate cancer (mCRPC), in patients who have not responded to previous treatments. For this application, extensive clinical data are available, and safety data of several Ac-225 based PSMA ligands have been reported. While effective, Ac-225 therapy is associated with side effects, most notably xerostomia (dry mouth), as well as potential hematologic and nephrotoxicity [31,32]. Ongoing trials are still being conducted to focus on improving safety protocols and production methods to make this promising therapy more widely available and highlight future direction as well. Deliverable D4.3 12 We here summarise the current clinical safety data for Ac-225 based on a structured literature review (https://zenodo.org/records/16986225)[33], which has been submitted for publication by WP4 members within the PRISMAP project (see Annex 3). 4.2.1 Clinical safety data The literature review was intended to address only data on the safety of Actinium-225 radiopharmaceuticals published to date. A comprehensive literature search was conducted using two bibliographic databases, ClinicalTrials.gov and PubMed/MEDLINE. The following terms were used to construct a search: (A) "Actinium" OR "Ac-225" OR "225Ac" OR "[225Ac]Ac" AND (B) "safety" OR "toxicity" OR "side-effect". Table 2. Published relevant safety data from studies utilising Ac-225 radiopharmaceuticals Table 2 summarizes the published and valuable safety data from studies utilising Ac-225 conjugated to different ligands in various cancer types. PSMA ligands are the most studied among all the retrieved papers and conference abstracts. In total, we collected 24 studies involving PSMA ligands, including more than 1400 patients, published between 2016-2025. As seen in the table, the administered activity and follow-up period varied as well. Either high-grade or low-grade toxicity reported based on CTCAE criteria [34], xerostomia (dry mouth) is among the most frequent adverse events, followed by hematologic and nephrologic toxicities. The second most studied ligand is DOTATATE in different types of NET. Besides the hematoand nephrological adverse events, it is worth mentioning that gastrointestinal signs and weight loss were reported as frequent adverse events as well, although some of the adverse events would be due to the renal protection solution that was concurrently administered to the patients during the TAT [35,36]. Another SSTR targeted ligand Ligand Year (Study No.) Pts/Cancer type Dose range Reported Follow-up (months) Reported adverse events PSMA 2016-2025(24) 1491/prostate cancer 0,1-0,15 MBq/kg 2,7-9 MBq/Cycle 7.4 ± 1.5 MBq one study) 5.5-60 High-grade and low-grade dry mouth, hemato- & nephrologic, less frequent hepatologic, fatigue, weight loss Low-grade toxicities were more frequent DOTATATE 2020-2024(8) 173/NET(GEP ¶gangliom a) 0,1-0,12 MBq/kg – 7,4 MBq (one study) 8-30 A few high-grade hemato and nephrologic One study: high-grade gastritis, weight loss, flushing Low-grade adverse events: hematological, loss of appetite and followed by nephrologic toxicities DOTATOC 2022 (2) 80/NET 0,1-0,15 MBq/kg 20 MBq per cycle 25&48 Only two high-grade nephrologic toxicity Low-grade hematological adverse events FAP(3BP-3940) 2023-2024(3) 121/various cancers 14 ± 10 MBq 33 (one study) More low-grade hematologic and nephrologic Hepatologic, nausea, alopecia and pain flair DOTA-LM3 2024 (1) 28/NET 44 cycles in total 23 Hematologic followed by nephrological adverse events Rosopatamab Tetraxetan(DO TA-huJ591) 2024 (1) 32/Prostate cancer 13.3 to 93.3 KBq/Kg N/A Hematological toxicities Lintuzumab(hu manised CD33) 2024 (1) 23/Acute myeloid leukemia 0.75 µCi/kg N/A Hematological adverse event Severe mucositis in 5 patients DOTASubstance P 2021-2023 (2) 24/Glial tumours 10-35MBq per cycle locoregional 6.9 Short term perifocal oedema, 1 high grade hematotoxicity Deliverable D4.3 13 binding Ac-225 is DOTATOC. According to two studies, a few events of high-grade toxicities were reported during the follow-up period. The other ligands that are stated within the table are less frequently investigated. In three articles and abstracts FAP(3BP-3940) utilised in different cancer types. Although only one study mentioned the follow-up period, the most reported adverse events are low-grade hematologic and nephrologic, followed by hepatological, nausea, pain flare and alopecia. As observed in other NET patients, conjugated Ac-225 DOTALM3, in 23 months of follow-up, hematological and renal adverse events are the most reported toxicities [37]. One study, in prostate cancer, investigated Ac-225 Rosopatamab Tetraxetan(DOTA-huJ591) and reported hematological adverse events as the commonest toxicity. The other trial( NCT03441048) [38] stated in acute myeloid leukemia that 225AcLintuzumab (humanised CD33) in 23 patients, they saw five events of mucosities and hematologic toxicities as well. DOTA-substance P conjugated Ac-225 was investigated in two studies. They included lowand high-grade glioma and administered loco-regional intracavitary dose(s) of radiotracer. The authors reported that the therapy was well tolerated with transient non-severe toxicities and therefore might be safe. Table 3. Registered trials retrieved from ClinicalTrials.gov database involving Ac-225 (Data included until August 2025) NCT Number Study Status Cancer Type Radiotracer ligand Study Result Study Type NCT04506567 SUSPENDED Prostate Cancer 225Ac-J591 NO INTERVENTIONAL NCT04576871 NOT RECRUITING Prostate Cancer 225Ac-J591 NO INTERVENTIONAL NCT03746431 RECRUITING Advanced various Solid Tumours 225Ac-FPI-1434 NO INTERVENTIONAL NCT04886986 SUSPENDED Prostate Cancer 225Ac-J591 NO INTERVENTIONAL NCT04946370 RECRUITING Prostate Cancer 225Ac-J591 NO INTERVENTIONAL NCT05363111 RECRUITING Plasma Cell Myeloma 225AcDOTAdaratumumab NO INTERVENTIONAL NCT05605522 RECRUITING Advanced various Solid Tumours 225AcFPI-2059 NO INTERVENTIONAL NCT04597411 RECRUITING Prostate Cancer 225Ac-PSMA-617 NO INTERVENTIONAL NCT05204147 RECRUITING Advanced metastatic different cancers 225Ac -DOTAM5A(anti CEA Ab) NO INTERVENTIONAL NCT05595460 RECRUITING SCLC, Extensive Stage RYZ101 NO INTERVENTIONAL NCT05219500 RECRUITING Prostate Cancer 225Ac-PSMA-I&T NO INTERVENTIONAL NCT03441048 COMPLETED Acute Myeloid Leukemia 225Ac-Lintuzumab NO INTERVENTIONAL NCT05567770 WITHDRAWN Prostate Cancer 225Ac-J591 NO INTERVENTIONAL NCT05477576 RECRUITING GEP-NET RYZ101 NO INTERVENTIONAL NCT04644770 RECRUITING Prostate Cancer 225Ac-JNJ69086420(Human Kallikrein-2 Ab) NO INTERVENTIONAL NCT03867682 RECRUITING Acute Myeloid Leukemia 225Ac-Lintuzumab NO INTERVENTIONAL NCT03276572 COMPLETED Prostate Cancer 225Ac-J591 YES INTERVENTIONAL In Table 3, we retrieved the registered trials from ClinicalTrials.gov database based on the inclusion criteria and search strategy, given in detail in our comprehensive review on the safety profile of Ac-225). There are different ligands targeting various cancer cells that are studying now. Officially, only two trials have been Deliverable D4.3 14 completed. However, regarding the published safety data, only one study released the adverse events (NCT03441048), which is mentioned above. Several studies have shown that there have been no instances of serious acute adverse eventsduring or early after the radiotracer administrationor therapy termination due to adverse events. This is something that should be taken into consideration. In summary, although the retrieved and reviewed investigations faced some limitations, such as inhomogeneity, a rather small sample size, and the retrospective nature of studies, they depicted that Ac225 TAT could be considered safe and well-tolerated in general with an acceptable adverse event profile. The upcoming results from ongoing trials and information extracted from long-term toxicities associated with Ac225 therapy would pave the way to make strong statements regarding the safety and side effects of clinical administration of different Ac-225 radiotracers. 5. Conclusions This document provides information and data related to the pharmaceutical safety for the development and clinical translation of radiopharmaceuticals involving novel radionuclides. Current regulatory developments were reviewed, and aspects related to novel radionuclides were addressed. The standardisation of Nuclear Medicine Equipment in research laboratories and hospitals involved in clinical development and trials with novel radionuclides was exemplified in a dedicated study on Tb-161. Finally, a collection of data related to the non-clinical and clinical safety evidence for two clinically advanced therapeutic radionuclides, Tb-161 and Ac-225, was presented herein. This deliverable, therefore, provides an important document to establish the appropriate safety considerations for the clinical translation of novel radiopharmaceuticals using novel radionuclides and to develop the required documentation for approval by competent pharmaceutical authorities. These data need to be constantly monitored in the future and activities should be supported to strengthen standardised safety reporting of the use of such novel therapeutic radionuclides. PRISMAP partners will work to ensure continuation of these activities also in future, potential follow up projects. References 1. Decristoforo C, Hayashi SF, Bordeau C, Haddad F, Viertl D, Deville C, et al. Standards for clinical translation. 2022 May 31 [cited 2022 Jul 15]; Available from: https://zenodo.org/record/6599181 2. Vuleta G, Dondi M, Pascual T, Paez D, Medvedec M, Peștean C, et al. Quality Control of Nuclear Medicine Instrumentation and Protocol Standardisation [Internet]. 13th ed. Rep S, editor. European Association of Nuclear Medicine; 2017 [cited 2025 Jul 24]. Available from: https://eanmorg.staging.codecove.at/wp-content/uploads/2024/06/EANM_2017_TEchGuide_QualityControl.pdf 3. On behalf of the EANM Physics Committee:, Busemann Sokole E, With contribution from the EANM Working Group on Nuclear Medicine Instrumentation Quality Control:, Płachcínska A, Britten A, Lyra Georgosopoulou M, et al. Routine quality control recommendations for nuclear medicine instrumentation. Eur J Nucl Med Mol Imaging. 2010 Mar;37(3):662–71. 4. Lawhn-Heath C, Hope TA, Martinez J, Fung EK, Shin J, Seo Y, et al. Dosimetry in radionuclide therapy: the clinical role of measuring radiation dose. The Lancet Oncology. 2022 Feb;23(2):e75–87. 5. Park M, Mahmood A, Zimmerman RE, Limpa‐Amara N, Makrigiorgos GM, Moore SC. Adsorption of metallic radionuclides on plastic phantom walls. Medical Physics. 2008 Apr;35(4):1606–10. Deliverable D4.3 15 6. Marin I, Rydèn T, Van Essen M, Svensson J, Gracheva N, Köster U, et al. Establishment of a clinical SPECT/CT protocol for imaging of 161Tb. EJNMMI Phys. 2020 Dec;7(1):45. 7. Quantitative SPECT/CT—Technique and Clinical Applications. In: Recent Results in Cancer Research [Internet]. Cham: Springer International Publishing; 2020 [cited 2025 Jul 24]. p. 565–90. Available from: http://link.springer.com/10.1007/978-3-030-42618-7_17 8. Tran-Gia J, Lassmann M. Characterization of Noise and Resolution for Quantitative177Lu SPECT/CT with xSPECT Quant. J Nucl Med. 2019 Jan;60(1):50–9. 9. McIntosh L, Jackson P, Emmerson B, Buteau JP, Alipour R, Kong G, et al. Quantitative calibration of Tb161 SPECT/CT in view of personalised dosimetry assessment studies. EJNMMI Phys [Internet]. 2024 Feb 19 [cited 2025 Jul 24];11(1). Available from: https://ejnmmiphys.springeropen.com/articles/10.1186/s40658-024-00611-9 10. Lehenberger S, Barkhausen C, Cohrs S, Fischer E, Grünberg J, Hohn A, et al. The low-energy β− and electron emitter 161Tb as an alternative to 177Lu for targeted radionuclide therapy. Nuclear Medicine and Biology. 2011 Aug;38(6):917–24. 11. Van De Voorde M, Van Hecke K, Cardinaels T, Binnemans K. Radiochemical processing of nuclear-reactorproduced radiolanthanides for medical applications. Coordination Chemistry Reviews. 2019 Mar;382:103–25. 12. Tran-Gia J, Cicone F, Koole M, Giammarile F, Gear J, Deshayes E, et al. Rethinking Dosimetry: A European Perspective. J Nucl Med. 2025 May 22;jnumed.124.269378. 13. Müller C, Reber J, Haller S, Dorrer H, Bernhardt P, Zhernosekov K, et al. Direct in vitro and in vivo comparison of 161Tb and 177Lu using a tumour-targeting folate conjugate. Eur J Nucl Med Mol Imaging. 2014 Mar;41(3):476–85. 14. Borgna F, Barritt P, Grundler PV, Talip Z, Cohrs S, Zeevaart JR, et al. Simultaneous Visualization of 161Tband 177Lu-Labeled Somatostatin Analogues Using Dual-Isotope SPECT Imaging. Pharmaceutics. 2021 Apr 12;13(4):536. 15. Borgna F, Haller S, Rodriguez JMM, Ginj M, Grundler PV, Zeevaart JR, et al. Combination of terbium-161 with somatostatin receptor antagonists—a potential paradigm shift for the treatment of neuroendocrine neoplasms. Eur J Nucl Med Mol Imaging. 2022 Mar;49(4):1113–26. 16. Müller C, Umbricht CA, Gracheva N, Tschan VJ, Pellegrini G, Bernhardt P, et al. Terbium-161 for PSMAtargeted radionuclide therapy of prostate cancer. Eur J Nucl Med Mol Imaging. 2019 Aug;46(9):1919–30. 17. Wallimann RH, Mehta A, Mapanao AK, Köster U, Kneuer R, Schindler P, et al. Preclinical comparison of (radio)lanthanides using mass spectrometry and nuclear imaging techniques: biodistribution of lanthanide-based tumor-targeting agents and lanthanides in ionic form. Eur J Nucl Med Mol Imaging. 2025 Mar;52(4):1370–82. 18. Busslinger SD, Mapanao AK, Kegler K, Bernhardt P, Flühmann F, Fricke J, et al. Comparison of the tolerability of 161Tband 177Lu-labeled somatostatin analogues in the preclinical setting. Eur J Nucl Med Mol Imaging. 2024 Nov;51(13):4049–61. 19. Baum RP, Singh A, Kulkarni HR, Bernhardt P, Rydén T, Schuchardt C, et al. First-in-Humans Application of 161Tb: A Feasibility Study Using 161Tb-DOTATOC. J Nucl Med. 2021 Oct;62(10):1391–7. Deliverable D4.3 16 20. Al-Ibraheem A, Abdlkadir AS, Sweedat DA, Maus S, Al-Rasheed U, Salah S, et al. From Despair to Hope: First Arabic Experience of 177Lu-PSMA and 161Tb-PSMA Therapy for Metastatic Castration-Resistant Prostate Cancer. Cancers. 2024 May 23;16(11):1974. 21. Abdlkadir AS, Abufara A, Al-Ibraheem A. Dual Radionuclide Therapy: The Synergistic Effects of [161Tb]TbPSMA and [177Lu]Lu-PSMA in Advanced Prostate Cancer Post [177Lu]Lu-PSMA Failure. Nucl Med Mol Imaging. 2024 Oct;58(6):381–2. 22. Chirindel A, Nicolas GP, Westerbergh F, McDougall L, Schmid DE, Geistlich S, et al. First-in-human administration of [161Tb]Tb-SibuDAB and comparative dosimetry with standard [177Lu]Lu-PSMA-I&T as part of the PROGNOSTICS phase Ia study. Eur J Nucl Med Mol Imaging. 2025 Apr;52(5):1628–30. 23. Fricke J, Westerbergh F, McDougall L, Favaretto C, Christ E, Nicolas GP, et al. First-in-human administration of terbium-161-labelled somatostatin receptor subtype 2 antagonist ([161Tb]Tb-DOTALM3) in a patient with a metastatic neuroendocrine tumour of the ileum. Eur J Nucl Med Mol Imaging. 2024 Jul;51(8):2517–9. 24. Schaefer-Schuler A, Burgard C, Blickle A, Maus S, Petrescu C, Petto S, et al. [161Tb]Tb-PSMA-617 radioligand therapy in patients with mCRPC: preliminary dosimetry results and intra-individual head-tohead comparison to [177Lu]Lu-PSMA-617. Theranostics. 2024;14(5):1829–40. 25. Buteau JP, Kostos L, Alipour R, Jackson P, McInstosh L, Emmerson B, et al. Clinical Trial Protocol for VIOLET: A Single-Center, Phase I/II Trial Evaluation of Radioligand Treatment in Patients with Metastatic Castration-Resistant Prostate Cancer with [161Tb]Tb-PSMA-I&T. J Nucl Med. 2024 Aug;65(8):1231–8. 26. Buteau JP, Kostos L, Jackson PA, Xie J, Haskali MB, Alipour R, et al. First-in-human results of terbium-161 [161Tb]Tb-PSMA-I&T dual beta–Auger radioligand therapy in patients with metastatic castrationresistant prostate cancer (VIOLET): a single-centre, single-arm, phase 1/2 study. The Lancet Oncology [Internet]. 2025 Jul [cited 2025 Jul 24]; Available from: https://linkinghub.elsevier.com/retrieve/pii/S1470204525003328 27. Jacobs N, Solomon T, Kolade O, Hlongwa K, More S. Use of Terbium-161 [161Tb]Tb-DOTATATE in Recurrent Paraganglioma. Clinical Nuclear Medicine [Internet]. 2025 May 16 [cited 2025 Jul 24]; Available from: https://journals.lww.com/10.1097/RLU.0000000000005897 28. Lawal IO, Abubakar SO, Ndlovu H, Mokoala KMG, More SS, Sathekge MM. Advances in Radioligand Theranostics in Oncology. Mol Diagn Ther. 2024 May;28(3):265–89. 29. Jadvar H. Targeted α-Therapy in Cancer Management: Synopsis of Preclinical and Clinical Studies. Cancer Biotherapy and Radiopharmaceuticals [Internet]. 2020 Sep 1 [cited 2025 Aug 10];35(7):475–84. Available from: https://www.liebertpub.com/doi/10.1089/cbr.2019.3340 30. A. Scheinberg D, R. McDevitt M. Actinium-225 in Targeted Alpha-Particle Therapeutic Applications. CRP [Internet]. 2011 Oct 1 [cited 2025 Aug 10];4(4):306–20. Available from: http://www.eurekaselect.com/openurl/content.php?genre=article&issn=18744710&volume=4&issue=4&spage=306 31. Besiroglu H, Kadihasanoglu M. The Safety and Efficacy of Targeted Alpha Therapy, Ac‐225 Prostate‐ Specific Membrane Antigen, in Patients With Metastatic Castration‐Resistant Prostate Cancer: A Systematic Review and Meta‐Analysis. The Prostate [Internet]. 2025 May [cited 2025 Jul 28];85(6):541– 57. Available from: https://onlinelibrary.wiley.com/doi/10.1002/pros.24857 Deliverable D4.3 17 32. Al-Ibraheem A, Moghrabi S, Sathekge MM, Abdlkadir AS. Evaluating Xerostomia as a side effect of [255Ac]Ac-PSMA therapy in prostate cancer: a systematic review and meta-analysis. Eur J Nucl Med Mol Imaging [Internet]. 2025 Jul [cited 2025 Jul 28];52(8):2906–17. Available from: https://link.springer.com/10.1007/s00259-025-07168-4 33. Decristoforo C, Roustaei H, D’Alessandria C. Navigating the Safety Profile of Actinium-225 Targeted Alpha Therapy: A Comprehensive Review [Internet]. Zenodo; 2025 [cited 2025 Aug 28]. Available from: https://zenodo.org/doi/10.5281/zenodo.16986225 34. Common Terminology Criteria for Adverse Events (CTCAE) Version 5.0 [Internet]. 2017. Available from: https://dctd.cancer.gov/research/ctep-trials/for-sites/adverse-events/ctcae-v5-8x11.pdf 35. Vorster M, Grana CM, Travascio L, Sathekge MM. Alpha therapies: where and when is the future in neuroendocrine tumours? Clin Transl Imaging [Internet]. 2025 Mar 26 [cited 2025 Jul 25]; Available from: https://link.springer.com/10.1007/s40336-025-00692-1 36. Kratochwil C, Apostolidis L, Rathke H, Apostolidis C, Bicu F, Bruchertseifer F, et al. Dosing 225AcDOTATOC in patients with somatostatin-receptor-positive solid tumors: 5-year follow-up of hematological and renal toxicity. European Journal of Nuclear Medicine and Molecular Imaging [Internet]. 2021 Dec 1;49(1):54–63. Available from: https://doi.org/10.1007/s00259-021-05474-1 37. Perrone E. EANM’24 Abstract Book Congress Oct 19-23, 2024. Eur J Nucl Med Mol Imaging [Internet]. 2024 Sep [cited 2025 Jul 25];51(S1):1–1026. Available from: https://link.springer.com/10.1007/s00259024-06838-z 38. Abedin S, Brodin P, Chen M, Rotibi M, Syed U, Desai A, et al. <strong>Safety and Dosimetric Analysis of Lintuzumab-Ac225 in Combination with Intensive CLAG-M Chemotherapy in Patients with Relapsed/Refractory AML</strong>. J Nucl Med [Internet]. 2024 Jun 1;65(supplement 2):241340. Available from: http://jnm.snmjournals.org/content/65/supplement_2/241340.abstract