OLINDA/EXM 2-The Next-generation Personal Computer Software for Internal Dose Assessment in Nuclear Medicine.

ABSTRACT: The OLINDA/EXM version 2.0 personal computer code was created as an upgrade to the widely used OLINDA/EXM 1.0 and 1.1 codes. This paper documents the upgrades that were implemented. New decay data and anthropomorphic and biokinetic models were implemented in the software, and the software alpha and beta tested. Agreement of doses between the OLINDA/EXM codes 1 and 2 was very good. Use of the new anthropomorphic and biokinetic models results in understandable differences between the codes. Previous models were retained in the new code, and those results were identical to those in the previous code. OLINDA/EXM 2.0 represents an upgrade from version 1, with new modeling data recommended by the international community. It standardizes internal dose calculations for dose assessments in clinical trials with radiopharmaceuticals, theoretical calculations for existing pharmaceuticals, teaching, and other purposes.

Comparison of absorbed dose extrapolation methods for mouse-to-human translation of radiolabelled macromolecules.

BACKGROUND: Extrapolation of human absorbed doses (ADs) from biodistribution experiments on laboratory animals is used to predict the efficacy and toxicity profiles of new radiopharmaceuticals. Comparative studies between available animal-to-human dosimetry extrapolation methods are missing. We compared five computational methods for mice-to-human AD extrapolations, using two different radiopharmaceuticals, namely [111In]CHX-DTPA-scFv78-Fc and [68Ga]NODAGA-RGDyK. Human organ-specific time-integrated activity coefficients (TIACs) were derived from biodistribution studies previously conducted in our centre. The five computational methods adopted are based on simple direct application of mice TIACs to human organs (M1), relative mass scaling (M2), metabolic time scaling (M3), combined mass and time scaling (M4), and organ-specific allometric scaling (M5), respectively. For [68Ga]NODAGA-RGDyK, these methods for mice-to-human extrapolations were tested against the ADs obtained on patients, previously published by our group. Lastly, an average [68Ga]NODAGA-RGDyK-specific allometric parameter αnew was calculated from the organ-specific biological half-lives in mouse and humans and retrospectively applied to M3 and M4 to assess differences in human AD predictions with the α = 0.25 recommended by previous studies. RESULTS: For both radiopharmaceuticals, the five extrapolation methods showed significantly different AD results (p < 0.0001). In general, organ ADs obtained with M3 were higher than those obtained with the other methods. For [68Ga]NODAGA-RGDyK, no significant differences were found between ADs calculated with M3 and those obtained directly on human subjects (H) (p = 0.99; average M3/H AD ratio = 1.03). All other methods for dose extrapolations resulted in ADs significantly different from those calculated directly on humans (all p ≤ 0.0001). Organ-specific allometric parameters calculated using combined experimental [68Ga]NODAGA-RGDyK mice and human biodistribution data varied significantly. ADs calculated with M3 and M4 after the application of αnew = 0.17 were significantly different from those obtained by the application of α = 0.25 (both p < 0.001). CONCLUSIONS: Available methods for mouse-to-human dosimetry extrapolations provided significantly different results in two different experimental models. For [68Ga]NODAGA-RGDyK, the best approximation of human dosimetry was shown by M3, applying a metabolic scaling to the mouse organ TIACs. The accuracy of more refined extrapolation algorithms adopting model-specific metabolic scaling parameters should be further investigated.

RADAR Guide: Standard Methods for Calculating Radiation Doses for Radiopharmaceuticals, Part 2-Data Analysis and Dosimetry.

This paper presents standardized methods for performing dose calculations for radiopharmaceuticals. Various steps in the process are outlined, with some specific examples given. Special models for calculating time-activity integrals (urinary bladder, intestines) are also reviewed. This article can be used as a template for designing and executing kinetic studies for calculating radiation dose estimates from animal or human data.

RADAR Guide: Standard Methods for Calculating Radiation Doses for Radiopharmaceuticals, Part 1-Collection of Data for Radiopharmaceutical Dosimetry.

This paper presents standardized methods for collecting data to be used in performing dose calculations for radiopharmaceuticals. Various steps in the process are outlined, with some specific examples given. This document can be used as a template for designing and executing kinetic studies for calculating radiation dose estimates, from animal or human data.

First in Human Evaluation and Dosimetry Calculations for Peptide 124I-p5+14-a Novel Radiotracer for the Detection of Systemic Amyloidosis Using PET/CT Imaging.

PURPOSE: Accurate diagnosis of amyloidosis remains a significant clinical challenge and unmet need for patients. The amyloid-reactive peptide p5+14 radiolabeled with iodine-124 has been developed for the detection of amyloid by PET/CT imaging. In a first-in-human evaluation, the dosimetry and tissue distribution of 124I-p5+14 peptide in patients with systemic amyloidosis. Herein, we report the dosimetry and dynamic distribution in the first three enrolled patients with light chain-associated (AL) amyloidosis. PROCEDURES: The radiotracer was assessed in a single-site, open-label phase 1 study (NCT03678259). The first three patients received a single intravenous infusion of 124I-p5+14 peptide (≤37 MBq). Serial PET/CT imaging was performed during the 48 h post-infusion. Dosimetry was determined as a primary endpoint for each patient and gender-averaged mean values were calculated. Pharmacokinetic parameters were estimated from whole blood radioactivity measurements and organ-based time activity data. Lastly, the biodistribution of radiotracer in major organs was assessed visually and compared to clinically appreciated organ involvement. RESULTS: Infusion of the 124I-p5+14 was well tolerated with rapid uptake in the heart, kidneys, liver, spleen, pancreas, and lung. The gender-averaged whole-body effective radiation dose was estimated to be 0.23 (± 0.02) mSv/MBq with elimination of the radioactivity via renal and gastrointestinal routes. The whole blood elimination t1/2 of 21.9 ± 7.6 h. Organ-based activity concentration measurements indicated that AUClast tissue:blood ratios generally correlated with the anticipated presence of amyloid. Peptide uptake was observed in 4/5 clinically suspected organs, as noted in the medical record, as well as six anatomic sites generally associated with amyloidosis in this population. CONCLUSION: Peptide 124I-p5+14 rapidly distributes to anatomic sites consistent with the presence of amyloid in patients with systemic AL. The dosimetry estimates established in this cohort are acceptable for whole-body PET/CT imaging. Pharmacokinetic parameters are heterogeneous and consistent with uptake of the tracer in an amyloid compartment. PET/CT imaging of 124I-p5+14 may facilitate non-invasive detection of amyloid in multiple organ systems.

Oral Administration of 99mTechnetium-Labeled Heparin in Eosinophilic Esophagitis.

OBJECTIVE: To determine if heparin labeled with 99mTechnetium (99mTc) could be an imaging probe to detect eosinophil-related inflammation in eosinophilic esophagitis and to determine the biodistribution and radiation dosimetry of 99mTc-heparin oral administration using image-based dosimetry models with esophageal modeling. METHODS: Freshly prepared 99mTc-heparin was administered orally to 5 research subjects. Radioactivity was measured by whole-body scintigraphy and single-photon emission computed tomography during the 24 hours postadministration. Following imaging, endoscopic examination was performed. The biodistribution of esophageal radioactivity was compared with endoscopic findings, eosinophil counts in biopsy tissues, and immunostaining for eosinophil granule major basic protein-1 (eMBP1). These studies were conducted from July 1, 2013, until April 22, 2017. RESULTS: Oral administration of 99mTc-heparin was well tolerated in all 5 subjects. The entire esophagus could be visualized dynamically during oral administration. Bound esophageal radioactivity marked areas of inflammation as judged by endoscopy scores, by eosinophils per high power field and by localization of eMBP1 using immunostaining. Ninety percent of the radioactivity did not bind to the esophagus and passed through the gastrointestinal tract. CONCLUSION: The biodistribution of ingested 99mTc-heparin is almost exclusively localized to the gastrointestinal tract. Radiation exposure was highest in the lower gastrointestinal tract and was comparable with other orally administered diagnostic radiopharmaceuticals. The use of swallowed 99mTc-heparin may aid in assessing eosinophil-related inflammation in the esophagus.

NANETS/SNMMI Procedure Standard for Somatostatin Receptor-Based Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE.

With the recent approval of 177Lu-DOTATATE for use in gastroenteropancreatic neuroendocrine tumors, access to peptide receptor radionuclide therapy is increasing. Representatives from the North American Neuroendocrine Tumor Society and the Society of Nuclear Medicine and Molecular Imaging collaborated to develop a practical consensus guideline for the administration of 177Lu-DOTATATE. In this paper, we discuss patient screening, maintenance somatostatin analog therapy requirements, treatment location and room preparation, drug administration, and patient release as well as strategies for radiation safety, toxicity monitoring, management of potential complications, and follow-up. Controversies regarding the role of radiation dosimetry are discussed as well. This document is designed to provide practical guidance on how to safely treat patients with this therapy.

Internal radiation dosimetry of a 152Tb-labeled antibody in tumor-bearing mice.

BACKGROUND: Biodistribution studies based on organ harvesting represent the gold standard pre-clinical technique for dose extrapolations. However, sequential imaging is becoming increasingly popular as it allows the extraction of longitudinal data from single animals, and a direct correlation with deterministic radiation effects. We assessed the feasibility of mouse-specific, microPET-based dosimetry of an antibody fragment labeled with the positron emitter 152Tb [(T1/2 = 17.5 h, Eß+mean = 1140 keV (20.3%)]. Image-based absorbed dose estimates were compared with those obtained from the extrapolation to 152Tb of a classical biodistribution experiment using the same antibody fragment labeled with 111In. 152Tb was produced by proton-induced spallation in a tantalum target, followed by mass separation and cation exchange chromatography. The endosialin-targeting scFv78-Fc fusion protein was conjugated with the chelator p-SCN-Bn-CHX-A"-DTPA, followed by labeling with either 152Tb or 111In. Micro-PET images of four immunodeficient female mice bearing RD-ES tumor xenografts were acquired 4, 24, and 48 h after the i.v. injection of 152Tb-CHX-DTPA-scFv78-Fc. After count/activity camera calibration, time-integrated activity coefficients (TIACs) were obtained for the following compartments: heart, lungs, liver, kidneys, intestines, tumor, and whole body, manually segmented on CT. For comparison, radiation dose estimates of 152Tb-CHX-DTPA-scFv78-Fc were extrapolated from mice dissected 4, 24, 48, and 96 h after the injection of 111In-CHX-DTPA-scFv78-Fc (3-5 mice per group). Imaging-derived and biodistribution-derived organ TIACs were used as input in the 25 g mouse model of OLINDA/EXM® 2.0, after appropriate mass rescaling. Tumor absorbed doses were obtained using the OLINDA2 sphere model. Finally, the relative percent difference (RD%) between absorbed doses obtained from imaging and biodistribution were calculated. RESULTS: RD% between microPET-based dosimetry and biodistribution-based dose extrapolations were + 12, - 14, and + 17 for the liver, the kidneys, and the tumors, respectively. Compared to biodistribution, the imaging method significantly overestimates the absorbed doses to the heart and the lungs (+ 89 and + 117% dose difference, respectively). CONCLUSIONS: MicroPET-based dosimetry of 152Tb is feasible, and the comparison with organ harvesting resulted in acceptable dose discrepancies for body districts that can be segmented on CT. These encouraging results warrant additional validation using radiolabeled biomolecules with a different biodistribution pattern.

Dose calculation of radioactive nanoparticles: first considerations for the Design of Theranostic Agents.

The use of radioactive nanoparticles as imaging and therapeutic agents is increasing globally. Indeed, the use of these nanoparticles as perfect theranostic agent is highly anticipated in the pharmaceutical market. Among the radioactive nanoparticles, liposomes, solid lipid nanoparticles and polymeric nanoparticles are the most studied. However little information among adverse reactions, absorbed dose and correct dose to achieve the theranostic goal in a translational application is available. We developed a radioactive polymeric nanoparticle and calculated the absorbed dose in animal model (Wistar rats) using the OLINDA/EXM program. The results showed that some nanoparticle were uptake in five organs and minor elimination through the gastrointestinal and urinary pathways. The data corroborates the safe use in terms of blood-brain barrier and did not show high uptake by liver. The dosimetry data support the safe use of radioactive nanoparticles as theranostic agent. Graphical abstract ᅟ.

RADAR Dose Estimate Report: A Compendium of Radiopharmaceutical Dose Estimates Based on OLINDA/EXM Version 2.0.

A compendium of about 100 radiopharmaceuticals, based on the OLINDA/EXM version 2.0 software, is presented. A new generation of voxel-based, realistic human computational phantoms developed by the RADAR committee of the Society of Nuclear Medicine and Molecular Imaging, based on 2007 recommendations of the International Commission on Radiological Protection, was used to develop the dose estimates, and the most recent biokinetic models were used as well. These estimates will be made available in electronic form and can be modified and updated as models are changed and as new radiopharmaceuticals are added.

New Fetal Radiation Doses for 18F-FDG Based on Human Data.

Current standard values of fetal dosimetry deriving from 18F-FDG injection in pregnant women are estimated from animal data. The present communication offers a revision of fetal dosimetry values calculated from recently published human data, in which fetal 18F-FDG uptake was directly observed in vivo. The final doses were obtained from the observed time-integrated activity coefficients and a new generation of anthropomorphic voxel-based pregnancy phantoms.

Synthesis and preliminary PET imaging of 11C and 18F isotopologues of the ROS1/ALK inhibitor lorlatinib.

Lorlatinib (PF-06463922) is a next-generation small-molecule inhibitor of the orphan receptor tyrosine kinase c-ros oncogene 1 (ROS1), which has a kinase domain that is physiologically related to anaplastic lymphoma kinase (ALK), and is undergoing Phase I/II clinical trial investigations for non-small cell lung cancers. An early goal is to measure the concentrations of this drug in brain tumour lesions of lung cancer patients, as penetration of the blood-brain barrier is important for optimal therapeutic outcomes. Here we prepare both 11C- and 18F-isotopologues of lorlatinib to determine the biodistribution and whole-body dosimetry assessments by positron emission tomography (PET). Non-traditional radiolabelling strategies are employed to enable an automated multistep 11C-labelling process and an iodonium ylide-based radiofluorination. Carbon-11-labelled lorlatinib is routinely prepared with good radiochemical yields and shows reasonable tumour uptake in rodents. PET imaging in non-human primates confirms that this radiotracer has high brain permeability.