Introduction of the targeted alpha therapy (with Radium-223) into clinical practice in Japan: learnings and implementation

Theranostic Imaging Surrogates for Targeted Alpha Therapy: Progress in Production, Purification, and Applications

This article highlights recent developments of SPECT and PET diagnostic imaging surrogates for targeted alpha particle therapy (TAT) radiopharmaceuticals. It outlines the rationale for using imaging surrogates to improve diagnostic-scan accuracy and facilitate research, and the properties an imaging-surrogate candidate should possess. It evaluates the strengths and limitations of each potential imaging surrogate. Thirteen surrogates for TAT are explored: 133La, 132La, 134Ce/134La, and 226Ac for 225Ac TAT; 203Pb for 212Pb TAT; 131Ba for 223Ra and 224Ra TAT; 123I, 124I, 131I and 209At for 211At TAT; 134Ce/134La for 227Th TAT; and 155Tb and 152Tb for 149Tb TAT.

Radiation protection aspects for alpha therapies

The use of alpha emitting radiotherapeutics is increasing, with further growth expected due to a number of clinical trials currently running involving new alpha emitters. However, literature concerning radiation safety aspects of alpha emitting radionuclides is limited and most of the available literature concerns ²²³Ra. In general, the occupational exposure from alpha emitting radionuclides is expected to be low, as are doses to the public from external exposure. However, care must be taken to avoid skin contamination, inhalation, and ingestion. Not all alpha emitting radionuclides are identical, they often have very different associated decay chains and emissions. The decay chains and the manufacturing process should be carefully examined to identify any long-lived progeny or impurities. These may have an impact on the radiation safety processes required to limit occupational exposure and for waste management. Doses to the public must also be assessed, either arising directly from exposure to patients treated with radiotherapeutics, or via waste streams. Risk assessments should be in place when starting a new service covering all aspects of the preparation and administration, as well as any foreseeable incidents such as skin contamination or patient death, and the appropriate steps to take in these instances. It is imperative that with the increase in the use of alpha emitting radiotherapeutics more literature is published on radiation safety aspects, especially for new alpha emitting radiotherapeutics which often have very different characteristics than the currently established ones.

Extended single-dose toxicity study of [211At]NaAt in mice for the first-in-human clinical trial of targeted alpha therapy for differentiated thyroid cancer

Objective

Astatine (²¹¹At) is a promising alpha emitter as an alternative to iodine (¹³¹I). We are preparing the first-in-human (FIH) clinical trial of targeted alpha therapy for differentiated thyroid cancer in consultation with Pharmaceuticals and Medical Devices Agency. Here, we performed an extended single-dose toxicity examination under a reliability standard, as a preclinical safety assessment of [²¹¹At]NaAt to determine the FIH dose.

Methods

[²¹¹At]NaAt solution was injected into normal 6-week-old mice (male (n = 50) and female (n = 50), body weight: male 33.2 ± 1.7 g, female 27.3 ± 1.5 g), which were then divided into four groups: 5 MBq/kg (n = 20), 20 MBq/kg (n = 20), 50 MBq/kg (n = 30), saline control (n = 30). The mice were followed up for 5 days (primary evaluation point for acute toxicity: n = 80) or 14 days (n = 20: evaluation point for recovery) to monitor general condition and body weight change. At the end of the observation period, necropsy, blood test, organ weight measurement, and histopathological examination were performed. For body weight, blood test, and organ weight, statistical analyses were performed to compare data between the control and injected groups.

Results

No abnormal findings were observed in the general condition of mice. In the 50 MBq/kg group, males (days 3 and 5) showed a significant decrease in body weight compared with the control. However, necropsy did not differ significantly beyond the range of spontaneous lesions. In the blood test, males (50 MBq/kg) and females (50 MBq/kg) showed a decrease in white blood cell and platelet counts on day 5, and recovery on day 14. In the testis, a considerable weight decrease was observed on day 14 (50 MBq/kg), and multinucleated giant cells were observed in all mice, indicating a significant change related to the administration of [²¹¹At]NaAt.

Conclusions

In the extended single-dose toxicity study of [²¹¹At]NaAt, administration of high doses resulted in weight loss, transient bone marrow suppression, and pathological changes in the testis, which require consideration in the FIH clinical trial.

Clinical Perspectives of Theranostics

Theranostics is a precision medicine which integrates diagnostic nuclear medicine and radionuclide therapy for various cancers throughout body using suitable tracers and treatment that target specific biological pathways or receptors. This review covers traditional theranostics for thyroid cancer and pheochromocytoma with radioiodine compounds. In addition, recent theranostics of radioimmunotherapy for non-Hodgkin lymphoma, and treatment of bone metastasis using bone seeking radiopharmaceuticals are described. Furthermore, new radiopharmaceuticals for prostatic cancer and pancreatic cancer have been added. Of particular, F-18 Fluoro-2-Deoxyglucose (FDG) Positron Emission Tomography (PET) is often used for treatment monitoring and estimating patient outcome. A recent clinical study highlighted the ability of alpha-radiotherapy with high linear energy transfer (LET) to overcome treatment resistance to beta--particle therapy. Theranostics will become an ever-increasing part of clinical nuclear medicine.

Dosimetry of inhaled 219Rn progeny

During prostate cancer treatment with 223Ra. 219Rn (actinon) occurs and may be exhaled by the patient. Nurses and other hospital employees may inhale this radionuclide and its decay products. The alpha-emitting decay products of actinon deposited within a body will irradiate tissues and organs. Therefore. it is necessary to evaluate organ doses of actinon progeny. The purpose of this study is to set up a dosimetric method to assess dose coefficients for actinon progeny. The effective dose coefficients were calculated separately for three modes. The unattached mode which concerned the activity median thermodynamic diameter (AMTD) of 1 nm. and the nucleation and accumulation modes which are represented by activity median aerodynamic diameters (AMAD) of 60 and 500 nm respectively. The recent biokinetic models of actinon progeny developed in the Occupational Intakes of Radionuclides (OIR) publications series of the International Commission of Radiological Protection (ICRP) were implemented on BIOKMOD (Biokinetic Modeling) to calculate the number of nuclear transformations per activity intake of actinon progeny. The organ equivalent and effective dose coefficients were determined using the dosimetric approach of the ICRP. The inhalation dose coefficients of actinon progeny are dominated by the contribution of lung dose. The calculated dose coefficients of 211Pb and 211Bi are 5.78 × 10-8 and 4.84 × 10-9 Sv.Bq-1 for unattached particles (AMTD = 1 nm). and 1.4 × 10-8 and 3.55 × 10-9 Sv.Bq-1 for attached particles (AMAD = 60 nm). and 7.37 × 10-9 and 1.91 × 10-9 Sv.Bq-1 for attached particles (AMAD = 500 nm). These values are much closer to those of the recently published ICRP 137.

α-Emitting cancer therapy using 211 At-AAMT targeting LAT1

α-Methyl-l-tyrosine (AMT) has a high affinity for the cancer-specific l-type amino acid transporter 1 (LAT1). Therefore, we established an anti-cancer therapy, with ²¹¹ At-labeled α-methyl-l-tyrosine (²¹¹ At-AAMT) as a carrier of ²¹¹ At into tumors. ²¹¹ At-AAMT had high affinity for LAT1, inhibited tumor cell growth, and induced DNA double-stranded breaks in vitro. We evaluated the accumulation of ²¹¹ At-AAMT in vivo and the role of LAT1. Treatment with 0.4 MBq/mouse ²¹¹ At-AAMT inhibited tumor growth in the PANC-1 tumor model and 1 MBq/mouse ²¹¹ At-AAMT inhibited metastasis in the lung of the B16F10 metastasis model. Our results suggested that ²¹¹ At would be useful for anti-cancer therapy and that LAT1 is suitable as a target for radionuclide therapy.

Assessment of the radiation exposure of relatives and caregivers of patients treated with Ra-223 - Results of a German multicenter study

A multicenter study was conducted to assess the radiation exposure of relatives and caregivers of patients suffering from castration resistant prostate cancer with bone metastases and treated with Ra-223 dichloride in an outpatient setting. As Ra-223 and most of its progeny emit alpha particles, especially the internal exposure of persons in the patient's vicinity had to be evaluated.

METHODS

The external radiation was measured in distances of 1 m and 2 m. Wipe-tests were taken in the patients' homes to identify significant contaminations and evaluated by liquid scintillation counting. Samples of saliva and sweat were taken and measured using gamma spectrometry.

RESULTS

The external exposure from the patients measured 10-20min post injection (p. i.) was<0.080μSv/h in median in 1 m distance (range: below decision threshold (<DT) - 0.208μSv/h). Ra-223 was found in saliva (median 20-30 min p. i.: 27 Bq/g, range: 12.6 - 110 Bq/g) and excreted with sweat (median: 0.121 Bq/cm², range: 0.020 - 0.524 Bq/cm²) in the first 24h p. i. Contaminations in restrooms and kitchens were low (median: 0.026 - 0.215 mBq/cm², depending on location; range:<DT - 2.1 mBq/cm²).

CONCLUSIONS

The potential exposure of relatives by external irradiation and incorporation of Ra-223 excreted by the patient with saliva or sweat is estimated to be well below 1 mSv. No objections are seen regarding outpatient treatment.

Climbing the steps of the evidence-based medicine pyramid: highlights from Annals of Nuclear Medicine 2019

We aimed to provide an overview on research path in nuclear medicine climbing the steps of the Evidence-Based Medicine (EBM) pyramid using review of 14 subjectively selected papers out of 111 published in the Annals of Nuclear Medicine during January-December 2019. Following the structure of the EBM hierarchy, we chose at least one study for each step of the pyramid from the basis (pre-clinical research, expert opinion, case report and case series), to the middle (case-control and cohort studies, randomised controlled trials), towards the top (meta-analyses and systematic reviews). Additionally, we collected information on the promoter of each included study: investigator-initiated trials (IITs) vs industry-sponsored trials (ISTs). We found that pre-clinical studies are primarily focused on the development of novel molecular targets in cancer, with promising results. At the same time, clinical investigations deal with cardiological, neurological, infectious and oncological applications using both SPECT and PET modalities. Additionally, radionuclide therapy gained interest and is experiencing comprehensive clinical implementation. Our overview confirms the current central role of IITs as compared with ISTs. Challenges and future directions in Nuclear Medicine research are discussed.

Manual on the proper use of yttrium-90-labeled anti-P-cadherin antibody injection for radionuclide therapy in clinical trials

We present the guideline for use of yttrium-90-labeled anti-P-cadherin antibody injection for radionuclide therapy in clinical trials on the basis of radiation safety issues in Japan. This guideline was prepared by a study supported by the Ministry of Health, Labour, and Welfare, and approved by the Japanese Society of Nuclear Medicine. Treatment using yttrium-90-labeled anti-P-cadherin antibody injection in Japan should be carried out according to this guideline. Although this guideline is applied in Japan, the issues for radiation protection shown here are considered internationally useful as well. Only the original Japanese version is the formal document.

Quantitative measurement of 219Rn radioactivity in exhaled breath from patients with bone metastasis of castration-resistant prostate cancer treated with 223RaCl2

Background

The α-emitting radionuclide radium-223 (²²³Ra) is widely used for the treatment of bone metastasis in patients with castration-resistant prostate cancer. However, ²²³Ra decays into radon-219 (²¹⁹Rn) which is a noble-gas isotope, and ²¹⁹Rn may escape from patients treated with ²²³Ra via their respiration. In this study, we quantified the amount of ²¹⁹Rn contained in the breath of patients treated with ²²³Ra to estimate its effect on the internal exposure dose of caregivers.

Methods

A total of 12 breath samples were collected using a breath collection bag from a total of six patients treated with ²²³RaCl₂. Approximately 300 mL of exhaled breath was collected in a breath bag at 1 min and at 5 min after the start of ²²³RaCl₂ administration. The contents of each bag were measured using an HPGe detector, and the amount of ²¹⁹Rn was quantified based on the detection of the γ peak of ²¹¹Bi, which is a descendant nuclide of ²¹⁹Rn, persisting in the breath bag. The effective dose to caregivers arising from the inhalation of ²¹⁹Rn was estimated by referring to the scenario for the calculation of release criteria established for ¹³¹I therapy in Japan.

Results

A small peak for the 351-keV γ ray of ²¹¹Bi originating from the exhalation of ²¹⁹Rn was observed. Using the observed γ peak of ²¹¹Bi, the average amounts of ²¹⁹Rn per unit breath volume at 1 min and 5 min after the start of ²²³RaCl₂ administration were calculated as 90 ± 56 Bq/mL and 28 ± 9 Bq/mL, respectively. The effective dose of ²¹⁹Rn to caregivers was estimated to be 3.5 μSv per injection.

Conclusions

The amount of ²¹⁹Rn in the exhaled breath of patients treated with ²²³RaCl₂ was quantitatively calculated using breath collection bags. The internal radiation exposure of caregivers from ²¹⁹Rn in the exhaled breath of patients treated with ²²³RaCl₂ is relatively small.

Nuclear medicine practice in Japan: a report of the eighth nationwide survey in 2017

OBJECTIVE

Subcommittee on Survey of Nuclear Medicine Practice in Japan has performed a nationwide survey of nuclear medicine practice every 5 years since 1982 to survey contemporary nuclear medicine practice and its changes over the years.

METHODS

The subcommittee sent questionnaires, including the number and category of examinations as well as the kind and dose of the radiopharmaceuticals during the 30 days of June 2017, to all nuclear medicine institutes. The total numbers for the year 2017 were then estimated.

RESULTS

A total of 1132 institutes responded to the survey, including 351 PET centers. The recovery rate was 90.6%. The number of gamma cameras installed was 1332 in total, with 7.0% decrease in 5 years. Dual-head cameras and hybrid SPECT/CT scanners accounted for 88.2 and 23.6%, respectively. The number of single-photon tracer studies in 2017 was 1.08 million which means a decrease in 5.7% in 5 years and 23.6% in 10 years. All but neurotransmitter system, sentinel lymph node, and liver scintigraphy decreased. Bone scintigraphy was a leading examination (32.3%), followed by myocardial scintigraphy (24.1%) and cerebral perfusion study (18.0%) in order. SPECT studies showed an increase from 47.2% to 63.5%. PET centers have also increased from 295 to 389, as compared to the last survey. The 112 PET centers have installed one or two in-house cyclotrons. PET studies showed 24.5% increase in 5 years, with oncology accounting for 88.9%. ¹⁸F-FDG accounted for 98.2% (630,570 examinations). PET examinations using ¹¹C-methionine have decreased, with 2440 examinations in 2017. PET examinations using ¹³N-NH₃ have been increasing, with 2363 examinations in 2017. The number of PET studies using ¹¹C-PIB was 904. ¹³¹I-radioiodine targeted therapies showed an increase in 5 years (23.1%), including 4487 patients for thyroid cancer. Out-patient thyroid bed ablation therapy with 1,110 MBq of ¹³¹I accounted for 36.6% of cancer patients. The number of admission rooms increased from 135 to 157 in 5 years. The number of ²²³Ra targeted therapies for castration-resistant metastatic prostate cancer was 1194 patients.

CONCLUSIONS

Single-photon examinations showed a continuous tendency toward a decline in the survey. In contrast, the number of hybrid SPECT/CT scanner examinations has increased. PET/CT study and radionuclide targeted therapy have steadily increased.

Perspectives for Concepts of Individualized Radionuclide Therapy, Molecular Radiotherapy, and Theranostic Approaches

Radionuclide therapy (RNT) stands on the delivery of radiation to tumors or non-tumor target organs using radiopharmaceuticals that are designed to have specific affinity to targets. RNT is recently called molecular radiotherapy (MRT) by some advocators in order to emphasize its characteristics as radiotherapy and the relevance of dosimetry-guided optimization of treatment. Moreover, RNT requires relevant radiation protection standards because it employs unsealed radionuclides and gives therapeutic radiation doses in humans. On the basis of these radiation protection standards, the development and use of radiopharmaceuticals for combined application through diagnostics and therapeutics lead to theranostic approaches that will enhance the efficacy and safety of treatment by implementing dosimetry-based individualization.

Activities for the Development of Targeted Radionuclide Therapy in Japan

Targeted radionuclide therapy (TRT) is unique because of its efficacy and its theranostic feature in the era of precision medicine. So far, introduction of new TRT has not been going well in Japan due to several reasons including strict regulations, shortage of facilities for TRT, and insufficient reimbursement for TRT in clinic. Japanese community had several strategies to develop TRT in these 10 years, including the establishment of the National Conference for Nuclear Medicine Theranostics in which physicians, scientists, patients, people supporting patients, and industrial people gather. To promote TRT with supports from the government, the preparatory committee for the establishment of Japan Foundation of Medical Isotope Development (JAFMID) was launched. I would like to call TRT "Precision Nuclear Medicine." When we can add genomic information here, we can put it to new stage of cancer therapy. It is time for us.