Half-lives of 221Fr, 217At, 213Bi, 213Po and 209Pb from the 225Ac decay series

Quantitative SPECT/CT imaging of actinium-225 for targeted alpha therapy of glioblastomas

BACKGROUND

A new, alternative option for patients with recurrent glioblastoma is targeted alpha therapy (TAT), in the form of a local administration of substance P (neurokinin type 1 receptor ligand, NK-1) labelled with 225Ac. The purpose of the study was to confirm the feasibility of quantitative SPECT imaging of 225Ac, in a model reproducing specific conditions of TAT. In particular, to present the SPECT calibration methodology used, as well as the results of validation measurements and their accuracy. Additionally, to discuss the specific problems related to high noise in the presented case.

MATERIALS AND METHODS

All SPECT/CT scans were conducted using the Symbia T6 equipped with HE collimators, and acquired with multiple energy windows (three main windows: 440 keV, 218 keV, and 78 keV, with three lower scatter energy windows). A Jaszczak phantom with fillable cylindrical sources of various sizes was used to investigate quantitative SPECT/CT imaging characteristics. The planar sensitivity of the camera, an imaging calibration factor, and recovery coefficients were determined. Additionally, the 3D printed model of the glioblastoma tumour was developed and imaged to evaluate the accuracy of the proposed protocol.

RESULTS

Using the imaging calibration factor and recovery coefficients obtained with the Jaszczak phantom, we were able to quantify the activity in a 3D-printed model of a glioblastoma tumour with uncertainty of no more than 10% and satisfying accuracy.

CONCLUSIONS

It is feasible to perform quantitative 225Ac SPECT/CT imaging. However, there are still many more challenges that should be considered for further research on this topic (among others: accurate determination of ICF in the case of high background noise, better method of background estimation for recovery coefficient calculations, other methods for scatter correction than the dual-energy window scatter-compensation method used in this study).

Targeted Alpha Therapy: All We Need to Know about 225Ac's Physical Characteristics and Production as a Potential Theranostic Radionuclide

The high energy of α emitters, and the strong linear energy transfer that goes along with it, lead to very efficient cell killing through DNA damage. Moreover, the degree of oxygenation and the cell cycle state have no impact on these effects. Therefore, α radioisotopes can offer a treatment choice to individuals who are not responding to β- or gamma-radiation therapy or chemotherapy drugs. Only a few α-particle emitters are suitable for targeted alpha therapy (TAT) and clinical applications. The majority of available clinical research involves 225Ac and its daughter nuclide 213Bi. Additionally, the 225Ac disintegration cascade generates γ decays that can be used in single-photon emission computed tomography (SPECT) imaging, expanding the potential theranostic applications in nuclear medicine. Despite the growing interest in applying 225Ac, the restricted global accessibility of this radioisotope makes it difficult to conduct extensive clinical trials for many radiopharmaceutical candidates. To boost the availability of 225Ac, along with its clinical and potential theranostic applications, this review attempts to highlight the fundamental physical properties of this α-particle-emitting isotope, as well as its existing and possible production methods.

Radionuclide metrology: confidence in radioactivity measurements

Radionuclides, whether naturally occurring or artificially produced, are readily detected through their particle and photon emissions following nuclear decay. Radioanalytical techniques use the radiation as a looking glass into the composition of materials, thus providing valuable information to various scientific disciplines. Absolute quantification of the measurand often relies on accurate knowledge of nuclear decay data and detector calibrations traceable to the SI units. Behind the scenes of the radioanalytical world, there is a small community of radionuclide metrologists who provide the vital tools to convert detection rates into activity values. They perform highly accurate primary standardisations of activity to establish the SI-derived unit becquerel for the most relevant radionuclides, and demonstrate international equivalence of their standards through key comparisons. The trustworthiness of their metrological work crucially depends on painstaking scrutiny of their methods and the elaboration of comprehensive uncertainty budgets. Through meticulous methodology, rigorous data analysis, performance of reference measurements, technological innovation, education and training, and organisation of proficiency tests, they help the user community to achieve confidence in measurements for policy support, science, and trade. The author dedicates the George Hevesy Medal Award 2020 to the current and previous generations of radionuclide metrologists who have devoted their professional lives to this noble endeavour.

Status of the decay data for medical radionuclides: existing and potential diagnostic γ emitters, diagnostic β+ emitters and therapeutic radioisotopes

Recommended half-lives and specific well-defined emission energies and absolute emission probabilities are important input parameters that should be well-defined to assist in ensuring the diagnostic and therapeutic efficacy of individual radionuclides when applied in the field of nuclear medicine. Bearing in mind the nature of these requirements, approximately one hundred radionuclides have been considered and re-assessed as to whether their decay data are either adequately quantified, or require further in-depth measurements to improve their existing status and merit full re-evaluations of their decay schemes. The primary aim of such a review is to provide sufficient information on the existing and future requirements for such atomic and nuclear data.

Dosimetry in targeted alpha therapy. A systematic review: current findings and what is needed

Objective. A systematic review of dosimetry in Targeted Alpha Therapy (TAT) has been performed, identifying the common issues. Approach. The systematic review was performed in accordance with the PRISMA guidelines, and the literature was searched using the Scopus and PubMed databases. Main results. From the systematic review, three key points should be considered when performing dosimetry in TAT. (1) Biodistribution/Biokinetics: the accuracy of the biodistribution data is a limit to accurate dosimetry in TAT. The biodistribution of alpha-emitting radionuclides throughout the body is difficult to image directly, with surrogate radionuclide imaging, blood/faecal sampling, and animal studies able to provide information. (2) Daughter radionuclides: the decay energy of the alpha-emissions is sufficient to break the bond to the targeting vector, resulting in a release of free daughter radionuclides in the body. Accounting for daughter radionuclide migration is essential. (3) Small-scale dosimetry and microdosimetry: due to the short path length and heterogeneous distribution of alpha-emitters at the target site, small-scale/microdosimetry are important to account for the non-uniform dose distribution in a target region, organ or cell and for assessing the biological effect of alpha-particle radiation. Significance. TAT is a form of cancer treatment capable of delivering a highly localised dose to the tumour environment while sparing the surrounding healthy tissue. Dosimetry is an important part of treatment planning and follow up. Being able to accurately predict the radiation dose to the target region and healthy organs could guide the optimal prescribed activity. Detailed dosimetry models accounting for the three points mentioned above will help give confidence in and guide the clinical application of alpha-emitting radionuclides in targeted cancer therapy.

Global experience with PSMA-based alpha therapy in prostate cancer

PURPOSE

This review discusses the current state of prostate-specific membrane antigen (PSMA)-based alpha therapy of metastatic castration-resistant prostate cancer (mCRPC). With this in-depth discussion on the growing field of PSMA-based alpha therapy (PAT), we aimed to increase the interactions between basic scientists and physician-scientists in order to advance the field.

METHODS

To achieve this, we discuss the potential, current status, and opportunities for alpha therapy and strategies, attempted to date, and important questions that need to be addressed. The paper reviews important concepts, including whom to treat, how to treat, what to expect regarding treatment outcome, and toxicity, and areas requiring further investigations.

RESULTS

There is much excitement about the potential of this field. Much of the potential exists because these therapies utilize unique mechanisms of action, difficult to achieve with other conventional therapies.

CONCLUSION

A better understanding of the strengths and limitations of PAT may help in creating an effective therapy for mCRPC and design a rational combinatorial approach to treatment by targeting different tumor pathways.

Measurement of the half-life of excited nuclear states using liquid scintillation counting

This work presents measurements of the half-lives of excited nuclear states of ²³⁷Np and ⁵⁷Fe using a liquid scintillation (LS) spectrometer and a gamma detector. A novel approach for the determination of the half-lives of some excited states is presented which uses only LS counting data from a detector with two PMTs. The lifetime of the 1st and 2nd excited states of ⁵⁷Fe were obtained without the use of a gamma detector. The obtained value for the 59.54 keV level of ²³⁷Np is 67.60(25) ns. The obtained values for the 14.4 keV and 136.5 keV levels of ⁵⁷Fe are 97.90(40) ns and 8.780(36) ns, respectively. The half-life results from this study are consistent with the average value found in the reference decay data tables and have a lower uncertainty.

Development of [225Ac]Ac-PSMA-I&T for Targeted Alpha Therapy According to GMP Guidelines for Treatment of mCRPC

Recently, promising results of the antitumor effects were observed in patients with metastatic castration-resistant prostate cancer treated with ¹⁷⁷Lu-labeled PSMA-ligands. Radionuclide therapy efficacy may even be improved by using the alpha emitter Ac-225. Higher efficacy is claimed due to high linear energy transfer specifically towards PSMA positive cells, causing more double-strand breaks. This study aims to manufacture [²²⁵Ac]Ac-PSMA-I&T according to good manufacturing practice guidelines for the translation of [²²⁵Ac]Ac-PSMA-I&T into a clinical phase 1 dose escalation study. Quencher addition during labeling was investigated. Quality control of [²²⁵Ac]Ac-PSMA-I&T was based on measurement of Fr-221 (218 keV), in equilibrium with Ac-225 in approximately six half-lives of Fr-221 (T½ = 4.8 min). Radio-(i)TLC methods were utilized for identification of the different radiochemical forms, gamma counter for concentration determination, and HPGe-detector for the detection of the radiochemical yield. Radiochemical purity was determined by HPLC. The final patient dose was prepared and diluted with an optimized concentration of quenchers as during labeling, with an activity of 8–12 MBq (±5%), pH > 5.5, 100 ± 20 μg/dose, PSMA-I&T, radiochemical yield >95%, radiochemical purity >90% (up to 3 h), endotoxin levels of <5 EU/mL, osmolarity of 2100 mOsmol, and is produced according to current guidelines. The start of the phase I dose escalation study is planned in the near future.

Half-life determination of 213Bi and 209Pb by means of Cherenkov counting and detection with a NaI detector

An ²²⁵Ac source was prepared and combined with a dedicated setup to collect recoil atoms which are ejected as a consequence of alpha decay. Some targets were made of acrylic glass and were then placed in custom-built triple-to-double coincidence ratio (TDCR) counters to measure the Cherenkov counting rates as a function of time. Half-lives of ²¹³Bi and ²⁰⁹Pb were derived from the data. In addition, polyethylene films were used as targets to collect recoil atoms. These films were then measured in a well-type NaI detector to detect gamma rays. The analysis of the data yielded an independent result for the half-life of ²¹³Bi. Combining the results of both measurement techniques, T_1/2(²¹³Bi) = (45.60 ± 0.09) min was obtained as a final value for the half-life of ²¹³Bi. The half-life of ²⁰⁹Pb was found to be T_1/2(²⁰⁹Pb) = (195.1 ± 2.6) min.

TAG-72-Targeted α-Radionuclide Therapy of Ovarian Cancer Using 225Ac-Labeled DOTAylated-huCC49 Antibody

Radioimmunotherapy, an approach using radiolabeled antibodies, has had minimal success in the clinic with several β-emitting radionuclides for the treatment of ovarian cancer. Alternatively, radioimmunotherapy with α-emitters offers the advantage of depositing much higher energy over shorter distances but was thought to be inappropriate for the treatment of solid tumors, for which antibody penetration is limited to a few cell diameters around the vascular system. However, the deposition of high-energy α-emitters to tumor markers adjacent to a typical leaky tumor vascular system may have large antitumor effects at the tumor vascular level, and their reduced penetration in normal tissue would be expected to lower off-target toxicity. Methods: To evaluate this concept, DOTAylated-huCC49 was labeled with the α-emitter ²²⁵Ac to target tumor-associated glycoprotein 72-positive xenografts in a murine model of ovarian cancer. Results: ²²⁵Ac-labeled DOTAylated-huCC49 radioimmunotherapy significantly reduced tumor growth in a dose-dependent manner (1.85, 3.7, and 7.4 kBq), with the 7.4-kBq dose extending survival by more than 3-fold compared with the untreated control. Additionally, a multitreatment regime (1.85 kBq followed by 5 weekly doses of 0.70 kBq for a total of 5.4 kBq) extended survival almost 3-fold compared with the untreated control group, without significant off-target toxicity. Conclusion: These results establish the potential for antibody-targeted α-radionuclide therapy for ovarian cancer, which may be generalized to α-radioimmunotherapy in other solid tumors.

An Overview of Targeted Alpha Therapy with 225Actinium and 213Bismuth

Background:

Recent reports of the remarkable therapeutic efficacy of 225Ac-labeled PSMA-617 for therapy of metastatic castration-resistant prostate cancer have under-lined the clinical potential of targeted alpha therapy.

Objective and Conclusion:

This review describes methods for the production of 225Ac and its daughter nuclide 213Bi and summarizes the current clinical experience with both alpha emitters with particular focus on recent studies of targeted alpha therapy of bladder cancer, brain tu-mors, neuroendocrine tumors and prostate cancer.

Measurement of absolute γ-ray emission probabilities in the decay of 227Ac in equilibrium with its progeny

The emission probabilities of γ rays produced in the ²²⁷Ac decay series were determined by high-resolution γ-ray spectrometry of sources with standardised activity. The sources were prepared quantitatively on glass discs by drop deposition of a solution with ²²⁷Ac in radioactive equilibrium with its daughter nuclides. Their activity was measured by a primary standardisation technique based on alpha-particle counting at a defined low solid angle. Four laboratories performed γ-ray spectrometry and derived absolute γ-ray intensities. Mean values were calculated and compared with literature data and the currently recommended evaluated data. New values on certain γ-ray emission probabilities are proposed.

Targeted alpha therapy of mCRPC: Dosimetry estimate of 213Bismuth-PSMA-617

Purpose

PSMA-617 is a small molecule targeting the prostate-specific membrane antigen (PSMA). In this work, we estimate the radiation dosimetry for this ligand labeled with the alpha-emitter ²¹³Bi.

Methods

Three patients with metastatic prostate cancer underwent PET scans 0.1 h, 1 h, 2 h, 3 h, 4 h and 5 h after injection of ⁶⁸Ga-PSMA-617. Source organs were kidneys, liver, spleen, salivary glands, bladder, red marrow and representative tumor lesions. The imaging nuclide ⁶⁸Ga was extrapolated to the half-life of ²¹³Bi. The residence times of ²¹³Bi were forwarded to the instable daughter nuclides. OLINDA was used for dosimetry calculation. Results are discussed in comparison to literature data for ²²⁵Ac-PSMA-617.

Results

Assuming a relative biological effectiveness of 5 for alpha radiation, the dosimetry estimate revealed equivalent doses of mean 8.1 Sv _RBE5/GBq for salivary glands, 8.1 Sv _RBE5/GBq for kidneys and 0.52 Sv _RBE5/GBq for red marrow. Liver (1.2 Sv _RBE5/GBq), spleen (1.4 Sv _RBE5/GBq), bladder (0.28 Sv _RBE5/GBq) and other organs (0.26 Sv_RBE5/GBq) were not dose-limiting. The effective dose is 0.56 Sv _RBE5/GBq. Tumor lesions were in the range 3.2–9.0 Sv_RBE5/GBq (median 7.6 Sv_RBE5/GBq). Kidneys would limit the cumulative treatment activity to 3.7 GBq; red marrow might limit the maximum single fraction to 2 GBq. Despite promising results, the therapeutic index was inferior compared to ²²⁵Ac-PSMA-617.

Conclusions

Dosimetry of ²¹³Bi-PSMA-617 is in a range traditionally considered reasonable for clinical application. Nevertheless, compared to ²²⁵Ac-PSMA-617, it suffers from higher perfusion-dependent off-target radiation and a longer biological half-life of PSMA-617 in dose-limiting organs than the physical half-life of ²¹³Bi, rendering this nuclide as a second choice radiolabel for targeted alpha therapy of prostate cancer.

Electronic supplementary material

The online version of this article (10.1007/s00259-017-3817-y) contains supplementary material, which is available to authorized users.

A comparative evaluation of Ac225 vs Bi213 as therapeutic radioisotopes for targeted alpha therapy for cancer

The Ac225:Bi213 generator is the mainstay for preclinical and clinical studies of targeted alpha therapy for cancer. Both Ac225 (four alpha decays) and Bi213 (one alpha decay) are being used to label targeting vectors to form the alpha immunoconjugate for cancer therapy. This paper considers the radiobiological and economic aspects of Ac225 vs Bi213 as the preferred radioisotope for preclinical and clinical TAT. The in vitro and in vivo evidence and the role of DNA repair processes is examined. The maximum tolerance dose and therapeutic gain are endpoints for comparison. Ac225 has the higher therapeutic gain, when normalised to equal alpha production. However, the slow repair of double strand breaks reduces this advantage. Comparisons are made for the specific energy deposition in targeted and non-targeted cells, for endothelial cells by direct or indirect targeting, the need for sparing agents to save critical organs and cost considerations for preclinical and clinical trials and clinical use. Overall, Ac225 is found to have the better or equal performance to Bi213 at a much lower cost.

Targeted Radiolabeled Compounds in Glioma Therapy

Malignant gliomas of World Health Organization (WHO) grades II-IV represent the largest entity within the group of intrinsic brain tumors and are graded according to their pathophysiological features with survival times between more than 10 years (WHO II) and only several months (WHO IV). Gliomas arise from astrocytic or oligodendrocytic precursor cells and exhibit an infiltrative growth pattern lacking a clearly identifiable tumor border. The development of effective treatment strategies of the invasive tumor cell front represents the main challenge in glioma therapy. The therapeutic standard consists of surgical resection and, depending on the extent of resection and WHO grade, adjuvant external beam radiotherapy or systemic chemotherapy. Within the last decades, there has been no major improvement of the prognosis of patients with glioma. The consistent overexpression of neurokinin type 1 receptors in gliomas WHO grades II-IV has been used to develop a therapeutic substance P-based targeting system. A substance P-analogue conjugated to the DOTA or DOTAGA chelator has been labeled with different alpha-particle or beta-particle emitting radionuclides for targeted glioma therapy. The radiopharmaceutical has been locally injected into the tumors or the resection cavity. In several clinical studies, the methodology has been examined in adjuvant and neoadjuvant clinical settings. Although no large controlled series have so far been generated, the results of radiolabeled substance P-based targeted glioma therapy compare favorably with standard therapy. Recently, labeling with the alpha particle emitting Bi-213 has been found to be promising due to the high linear energy transfer and the very short tissue range of 0.08 mm. Further development needs to focus on the improvement of the stability of the compound and the application by dedicated catheter systems to improve the intratumoral distribution of the radiopharmaceutical within the prognostically critical infiltrative growing zone of the glioma.

Nuclear Data Evaluation for Mass Chain A=217:Odd-Proton Nuclei

Thallium (Tl81217), Bismuth (Bi83217), Astatine (At85217), Francium (Fr87217), Actinium (Ac89217) and Protactinium (Pa91217) are of odd-proton numbers among the mass chain A = 217. In the present work, the half-lives and gamma transitions for the six nuclei have been studied and adopted based on the recently published interactions or unevaluated nuclear data sets XUNDL. The Q (α) has been updated based on the recent published work of the Atomic Mass Evaluation AME2012 as well. Moreover, the total conversion electrons as well as the K-Shell to L-Shell, L-Shell to M-Shell and L-Shell to N-Shell Conversion Electron Ratios have been calculated using BrIcc code v2.3. An updated skeleton decay scheme for each of the above nuclei has been presented here. The decay hindrance factors (HF) calculated using the ALPHAD program, which is available from Brookhaven National Laboratory’s website, have been calculated for the α- decay data sets for ²²¹Fr-, ²²¹Ac- and ²²¹Pa- α-decays.

Effects of radiation type and delivery mode on a radioresistant eukaryote Cryptococcus neoformans

INTRODUCTION

Most research on radioresistant fungi, particularly on human pathogens such as Cryptococcus neoformans, involves sparsely-ionizing radiation. Consequently, fungal responses to densely-ionizing radiation, which can be harnessed to treat life-threatening fungal infections, remain incompletely understood.

METHODS

We addressed this issue by quantifying and comparing the effects of densely-ionizing α-particles (delivered either by external beam or by (213)Bi-labeled monoclonal antibodies), and sparsely-ionizing (137)Cs γ-rays, on Cryptococcus neoformans.

RESULTS

The best-fit linear-quadratic parameters for clonogenic survival were the following: α = 0.24 × 10(-2) Gy(-1) for γ-rays and 1.07 × 10(-2) Gy(-1) for external-beam α-particles, and β = 1.44 × 10(-5) Gy(-2) for both radiation types. Fungal cell killing by radiolabeled antibodies was consistent with predictions based on the α-particle dose to the cell nucleus and the linear-quadratic parameters for external-beam α-particles. The estimated RBE (for α-particles vs. γ-rays) at low doses was 4.47 for the initial portion of the α-particle track, and 7.66 for the Bragg peak. Non-radiological antibody effects accounted for up to 23% of cell death.

CONCLUSIONS

These results quantify the degree of C. neoformans resistance to densely-ionizing radiations, and show how this resistance can be overcome with fungus-specific radiolabeled antibodies.

Branched amphiphilic peptide capsules: cellular uptake and retention of encapsulated solutes

Branched amphiphilic peptide capsules (BAPCs) are peptide nano-spheres comprised of equimolar proportions of two branched peptide sequences bis(FLIVI)-K-KKKK and bis(FLIVIGSII)-K-KKKK that self-assemble to form bilayer delimited capsules. In two recent publications we described the lipid analogous characteristics of our BAPCs, examined their initial assembly, mode of fusion, solute encapsulation, and resizing and delineated their capability to be maintained at a specific size by storing them at 4°C. In this report we describe the stability, size limitations of encapsulation, cellular localization, retention and, bio-distribution of the BAPCs in vivo. The ability of our constructs to retain alpha particle emitting radionuclides without any apparent leakage and their persistence in the peri-nuclear region of the cell for extended periods of time, coupled with their ease of preparation and potential tune-ability, makes them attractive as biocompatible carriers for targeted cancer therapy using particle emitting radioisotopes. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

²¹³Bi-DOTATOC receptor-targeted alpha-radionuclide therapy induces remission in neuroendocrine tumours refractory to beta radiation: a first-in-human experience

Purpose

Radiopeptide therapy using a somatostatin analogue labelled with a beta emitter such as ⁹⁰Y/¹⁷⁷Lu-DOTATOC is a new therapeutic option in neuroendocrine cancer. Alternative treatments for patients with refractory disease are rare. Here we report the first-in-human experience with ²¹³Bi-DOTATOC targeted alpha therapy (TAT) in patients pretreated with beta emitters.

Methods

Seven patients with progressive advanced neuroendocrine liver metastases refractory to treatment with ⁹⁰Y/¹⁷⁷Lu-DOTATOC were treated with an intraarterial infusion of ²¹³Bi-DOTATOC, and one patient with bone marrow carcinosis was treated with a systemic infusion of ²¹³Bi-DOTATOC. Haematological, kidney and endocrine toxicities were assessed according to CTCAE criteria. Radiological response was assessed with contrast-enhanced MRI and ⁶⁸Ga-DOTATOC-PET/CT. More than 2 years of follow-up were available in seven patients.

Results

The biodistribution of ²¹³Bi-DOTATOC was evaluable with 440 keV gamma emission scans, and demonstrated specific tumour binding. Enduring responses were observed in all treated patients. Chronic kidney toxicity was moderate. Acute haematotoxicity was even less pronounced than with the preceding beta therapies.

Conclusion

TAT can induce remission of tumours refractory to beta radiation with favourable acute and mid-term toxicity at therapeutic effective doses.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-014-2857-9) contains supplementary material, which is available to authorized users.

Radioimmunotherapy with α-particle-emitting radionuclides

α-particle-emitting radionuclides are highly cytotoxic and are thus promising candidates for use in targeted radioimmunotherapy of cancer. Due to their high linear energy transfer (LET) combined with a short path length in tissue, α-particles cause severe DNA double-strand breaks that are repaired inaccurately and finally trigger cell death. For radioimmunotherapy, α-emitters such as 225Ac, 211At, 212Bi/212Pb, 213Bi and 227Th are coupled to antibodies via appropriate chelating agents. The α-emitter immunoconjugates preferably target proteins that are overexpressed or exclusively expressed on cancer cells. Application of α-emitter immunoconjugates seems particularly promising in treatment of disseminated cancer cells and small tumor cell clusters that are released during the resection of a primary tumor. α-emitter immunoconjugates have been successfully administered in numerous experimental studies for therapy of ovarian, colon, gastric, blood, breast and bladder cancer. Initial clinical trials evaluating α-emitter immunoconjugates in terms of toxicity and therapeutic efficacy have also shown positive results in patients with melanoma, ovarian cancer, acute myeloid lymphoma and glioma. The present problems in terms of availability of therapeutically effiective α-emitters will presumably be solved by use of alternative production routes and installation of additional production facilities in the near future. Therefore, clinical establishment of targeted α-emitter radioimmunotherapy as one part of a multimodal concept for therapy of cancer is a promising, middle-term concept.