Development of novel positron emitters for medical applications: nuclear and radiochemical aspects

Fast 3D kernel computation method for positron range correction in PET

Objective. The positron range is a fundamental, detector-independent physical limitation to spatial resolution in positron emission tomography (PET) as it causes a significant blurring of underlying activity distribution in the reconstructed images. A major challenge for positron range correction methods is to provide accurate range kernels that inherently incorporate the generally inhomogeneous stopping power, especially at tissue boundaries. In this work, we propose a novel approach to generate accurate three-dimensional (3D) blurring kernels both in homogenous and heterogeneous media to improve PET spatial resolution.Approach. In the proposed approach, positron energy deposition was approximately tracked along straight paths, depending on the positron stopping power of the underlying material. The positron stopping power was derived from the attenuation coefficient of 511 keV gamma photons according to the available PET attenuation maps. Thus, the history of energy deposition is taken into account within the range of kernels. Special emphasis was placed on facilitating the very fast computation of the positron annihilation probability in each voxel.Results. Positron path distributions of¹⁸F in low-density polyurethane were in high agreement with Geant4 simulation at an annihilation probability larger than 10^-2∼ 10^-3of the maximum annihilation probability. The Geant4 simulation was further validated with measured¹⁸F depth profiles in these polyurethane phantoms. The tissue boundary of water with cortical bone and lung was correctly modeled. Residual artifacts from the numerical computations were in the range of 1%. The calculated annihilation probability in voxels shows an overall difference of less than 20% compared to the Geant4 simulation.Significance. The proposed method is expected to significantly improve spatial resolution for non-standard isotopes by providing sufficiently accurate range kernels, even in the case of significant tissue inhomogeneities.

A new targetry system for production of zirconium-89 radioisotope with Cyclone-30 cyclotron

In this study, an efficient method for targetry and production of zirconium-89 radioisotope (89Zr) with Cyclone-30 cyclotron was developed. The preparation of a highly pure compressed yttrium oxide target material and design of a target made by copper for better heat transfer was performed. Electrodeposition of target with gold was done to prevent the entry of metallic impurities (copper, zinc and other trace metal elements). Nuclear reaction cross sections for optimization of production with new target and irradiation parameters of the target were evaluated. The prepared 89Zr in the form of [89Zr] Zr-oxalate had high radionuclidic purity (>99.9%) and a low chemical impurity concentration (<0.1 ppm for copper and zinc elements). The yield of 89Zr radioisotope production via the reaction of 89Y(p,n)89Zr was measured to be 77 ± 9.5 MBq/μAh (time of irradiation = 3, the current 20–30 µA). [89Zr] Zr-oxalate specific-activity was in the range 2.319641 × 104–3.479443 × 104 MBq/mmol of Oxalate.

Ion beam activation of natCu, natTi, natNi and measurement of product formation cross sections at low energy (<10 MeV)

In this study we investigated the production cross sections of natCu(p, x)63,65Zn, natTi(p, x)48V, natNi(p, x)55Co,61Cu and natCu(α, x)66,67,68Ga, natTi(α, x)49,51Cr, natNi(α, x)63,65Zn reactions in the low energy range using the foil activation technique. The samples were activated in vacuum at 5 MV tandem (Pelletron) accelerator installed at National Centre for Physics (NCP), Islamabad, Pakistan. The reaction products were identified with the help of off-line gamma ray spectroscopy system connected with Genie 2000 software. The data analysis revealed the production of different radioisotopes that have valuable importance in monitoring charged-particle beams and medical applications. The measured results were verified by comparing them with earlier evaluated data as well as with the theoretical values given in the TENDL-library based on TALYS-1.9 code calculations.

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.

The role of chemistry in accelerator-based production and separation of radionuclides as basis for radiolabelled compounds for medical applications

Radiochemical separations used in large scale routine production of diagnostic and therapeutic radionuclides at a particle accelerator for patient care are briefly outlined. The role of chemistry at various stages of development of a production route of a novel radionuclide, namely nuclear data measurement, high-current targetry, chemical processing and quality control of the product, is discussed in detail. Special attention is paid to production of non-standard positron emitters (e.g. 44gSc, 64Cu, 68Ga, etc.) at a cyclotron and novel therapeutic radionuclides (e.g. 67Cu, 225Ac, etc.) at an accelerator. Some typical examples of radiochemical methods involved are presented.

Special radionuclide production activities – recent developments at QST and throughout Japan

National Institutes for Quantum Science and Technology (QST), formerly known as the National Institute of Radiological Sciences (NIRS), has been engaged in work on radiopharmaceutical science using cyclotrons since 1974. Eight pioneering researchers founded the basis of this field of research at NIRS, and to the present, many researchers and technicians have accumulated both scientific and technical achievements, as well as inherited the spirit of research. Besides, in recent years, we have developed production systems with AVF-930 cyclotron for various ‘non-standard’ radioisotopes applied in both diagnosis and therapy. Here, we review the past 50 years of our activities on radioisotope and radiopharmaceutical development, as well as more recent activities.

Nuclear reaction data for medical and industrial applications: recent contributions by Egyptian cyclotron group

Measurement and evaluation of nuclear data of radioisotopes used as tracers are continuously underway in many laboratories to reach high accuracy for their use in production. We briefly mention some of the radionuclides useful for medical diagnostics and other industrial applications. The research group at the Egyptian cyclotron facility (EGCF) performed in collaboration with nuclear research centres and universities in many countries (Germany, Hungary, Finland, USA, Japan and Saudi Arabia) some measurements and evaluations of interesting nuclear reaction data. Nuclear reactions induced by p, d and α-particles on a wide variety of targets were extensively studied from threshold energy up to 50 MeV. Nuclear model code calculations, mainly using EMPIRE and TALYS, were performed for nuclear data validation. Proton and neutron activation of some industrially interesting samples were also studied as technological application of nuclear analytical techniques. Since the cyclotron facility is dedicated to development of the production routes of medical radioisotopes, this overview presents examples of optimization experiments to establish good production conditions.

An overview of nuclear data standardisation work for accelerator-based production of medical radionuclides in Pakistan

The standardisation of nuclear reaction cross section data is an integral part of optimisation of production routes of medical radionuclides. The production cross sections are available for the reactor and cyclotron produced radionuclides to be used for diagnostics or therapeutic procedures. The types of nuclear data needed, and the sources of their availability are summarized. The method of standardisation of charged-particle data is briefly described. A historical overview of research work in Pakistan in this direction is given. Examples of a few medically important radionuclides, such as 64Cu, 86Y, 89Zr, 103Pd, 186Re, etc., whose data were standardised and evaluated are highlighted. Calculated thick target yields from the recommended data are given. Some new directions in the nuclear data research are outlined.

China’s radiopharmaceuticals on expressway: 2014–2021

This review provides an essential overview on the progress of rapidly-developing China’s radiopharmaceuticals in recent years (2014–2021). Our discussion reflects on efforts to develop potential, preclinical, and in-clinical radiopharmaceuticals including the following areas: (1) brain imaging agents, (2) cardiovascular imaging agents, (3) infection and inflammation imaging agents, (4) tumor radiopharmaceuticals, and (5) boron delivery agents (a class of radiopharmaceutical prodrug) for neutron capture therapy. Especially, the progress in basic research, including new radiolabeling methodology, is highlighted from a standpoint of radiopharmaceutical chemistry. Meanwhile, we briefly reflect on the recent major events related to radiopharmaceuticals along with the distribution of major R&D forces (universities, institutions, facilities, and companies), clinical study status, and national regulatory supports. We conclude with a brief commentary on remaining limitations and emerging opportunities for China’s radiopharmaceuticals.

Positron Emission Intensity in the Decay of 86gY for Use in Dosimetry Studies

The β⁺-emitting radionuclide ^86gY (t_1/2 = 14.7 h) forms a matched-pair with the β⁻-emitting therapeutic radionuclide ⁹⁰Y (t_1/2 = 2.7 d) for theranostic application in medicine. This approach demands a precise knowledge of the positron emission probability of the PET nuclide which was until recently rather uncertain for ^86gY. In this work, an ^86gY source of high radionuclidic purity was prepared and a direct measurement of the positron emission intensity per 100 decay of the parent (hereafter “positron emission intensity”) was performed using high-resolution HPGe detector γ-ray spectroscopy. The electron capture intensity was also determined as an additional check by measuring the K_α and K_β X-rays of energies 14.1 and 15.8 keV, respectively, using a low energy HPGe detector. From those measurements, normalized values of 27.2 ± 2.0% for β⁺-emission and 72.8 ± 2.0% for EC were obtained. These results are in excellent agreement with values recently reported in the literature based on a detailed decay scheme study.

Cyclotron Production of PET Radiometals in Liquid Targets: Aspects and Prospects

The present review describes the methodological aspects and prospects of the production of Positron Emission Tomography (PET) radiometals in a liquid target using low-medium energy medical cyclotrons. The main objective of this review is to delineate and discuss the critical factors involved in the liquid target production of radiometals, including type of salt solution, solution composition, beam energy, beam current, the effect of irradiation duration (length of irradiation) and challenges posed by in-target chemistry in relation with irradiation parameters. We also summarize the optimal parameters for the production of various radiometals in liquid targets. Additionally, we discuss the future prospects of PET radiometals production in the liquid targets for academic research and clinical applications. Significant emphasis has been given to the production of ⁶⁸Ga using liquid targets due to the growing demand for ⁶⁸Ga labeled PSMA vectors, [⁶⁸Ga]- Ga-DOTATATE, [⁶⁸Ga]Ga-DOTANOC and some upcoming ⁶⁸Ga labeled radiopharmaceuticals. Other PET radiometals included in the discussion are ⁸⁶Y, ⁶³Zn and ⁸⁹Zr.

Evaluation of nuclear reaction cross section data of proton and deuteron induced reactions on 75As, with particular emphasis on the production of 73Se

75Se (T1/2 = 120 d), 73gSe (T1/2 = 7.1 h) and 72Se (T1/2 = 8.4 d) are important radioisotopes of selenium, being used in tracer studies, PET investigations and as a generator parent, respectively. Cross section data for the formation of those radionuclides in proton and deuteron induced reactions on 75As were critically analyzed up to about 70 MeV. A well-developed evaluation methodology was applied to generate the statistically fitted cross sections, based on the critically analyzed literature experimental data and the theoretical cross section values of three nuclear model codes ALICE-IPPE, TAYLS 1.9, and EMPIRE 3.2. Using the fitted cross sections the integral yield of each radionuclide was calculated. For the estimation of impurities, the integral yield of each radionuclide was compared with the yields of the other two radionuclides over a given energy region, and therefrom the energy range was suggested for the high purity production of each of the radionuclides 75Se, 73Se and 72Se. For production of the very important non-standard positron emitter 73Se via the 75As(p,3n)73Se reaction, the optimum energy range was deduced to be E p = 40 → 30 MeV, with a thick target yield of 1441 MBq/μAh and the 72,75Se impurity level of <0.1%.

Efficient trace-scale extraction method of reactor produced 199Au adequate for nuclear medicine applications

Production of no carrier-added (NCA) 199Au through natPt(n, γ) reaction and subsequent purification using liquid-liquid extraction from other radioisotopes is studied in the context of theranostic application. Comparative separation of NCA 199Au after dissolution of activated Pt target using three Cyanex compounds (Cyanex-272, Cyanex-302 and Cyanex-923) is evaluated. The extraction process is optimized in terms of the type of extractant, the concentration of extractant, extraction time and aqueous media (HNO3, NH4OH). Among these extractants, the Cynaex-923 is efficient and promising for rapid separation and production of NCA 199Au from HNO3 by high extraction %. Selective extraction of 199Au from other Pt and Ir radioisotopes is observed. High recovery of 199Au was obtained in the case of Cyanex-923 using 0.05 M thiourea dissolved in HCl or 2 M NaOH. Our results find the Cyanex-923 as a promising extractant for efficient separation of 199Au from irradiated Pt target with high yield (99%).

Evaluation of nuclear reaction cross sections for optimization of production of the important non-standard positron emitting radionuclide 89Zr using proton and deuteron induced reactions on 89Y target

⁸⁹Zr (T_1/2 = 3.27 d) is an important β⁺-emitting radionuclide of zirconium used in immuno PET. The excitation functions of the ⁸⁹Y(d,2n)⁸⁹Zr and ⁸⁹Y(p,n)⁸⁹Zr reactions were analyzed to deduce the optimum conditions for the high purity production of ⁸⁹Zr. The nuclear model codes ALICE-IPPE, EMPIRE 3.2 and TALYS 1.9 were used to check the consistency and reliability of the experimental data. A polynomial fit to the chosen data for each reaction gave the excitation function, which was then used for the integral yield calculation of the product. The amount of the major radioactive impurity ⁸⁸Zr was precisely analyzed for both the proton and the deuteron induced reactions on the ⁸⁹Y target.

Experimental investigation and theoretical evaluation of proton induced nuclear reactions on nickel

The cross-sections for proton-induced nuclear reactions on natural nickel were experimentally measured for the ^natNi(p,x)^60,61,64Cu, ^natNi(p,x)^55,57,58Co and ^natNi(p,x)⁵⁷Ni reactions from their respective thresholds up to 17 MeV proton energy. The stacked-foil technique in combination with HPGe γ-ray spectroscopy was used. Three codes were used in the theoretical calculations namely ALICE-IPPE, EMPIRE-3.2.2 and TENDL-2017. Comparison of the present results with the earlier reported experimental data and with the code results were carried out.

FLUKA simulation yields in a comparison with theoretical and experimental yields relevant to 89Zr produced in the 89Y(p,n) reaction

The high importance of zirconium-89 (T1/2 = 78.41 h) is related to its applications in medical imaging. It can be produced at low-energy cyclotrons by the reaction 89Y(p,n)89Zr. There exist several publications on its production at low and intermediate energies but there is discrepancy with simulated data. In this study we considered the experimental parameters for four different types of yttrium foil targets reported in literature. The experimental parameters considered were the target geometry, beam profile, and angle of the target relative to the beam during irradiation. The Monte-Carlo code FLUKA was used to calculate production yields. The resulting values obtained by FLUKA from pencil beam or spread energy beam were compared to the theoretical yields obtained from the excitation function and the experimental ones. The FLUKA prediction for 89Z-yield reached ≈50 MBq/μA · h which agrees to a high extent with experimental and theoretical yields reported for the different targets.

Positron-emitting radionuclides for applications, with special emphasis on their production methodologies for medical use

A survey of the positron-emitting radionuclides over the whole mass range of the Periodic Table of Elements was carried out. As already known, positrons are preferably emitted from light mass neutron deficient radionuclides. Their emission from heavier mass nuclides is rather rare. The applications of positron annihilation in three areas, namely materials research, plant physiology and medical diagnosis, are reported. The methods of production of positron emitters are discussed, with emphasis on radionuclides presently attracting more attention in theranostics and multimodal imaging. Some future perspectives of radionuclide development technologies are considered.

Radiobromine and radioiodine for medical applications

The halogens bromine and iodine have similar chemical properties and undergo similar reactions due to their closeness in Group 17 of the periodic chart. There are a number of bromine and iodine radionuclides that have properties useful for diagnosis and therapy of human diseases. The emission properties of radiobromine and radioiodine nuclides with half-lives longer than 1 h are summarized along with properties that make radionuclides useful in PET/SPECT imaging and β/Auger therapy, such that the reader can assess which of the radionuclides might be useful for medical applications. An overview of chemical approaches that have been used to radiolabel molecules with radiobromine and radioiodine nuclides is provided with examples. Further, references to a large variety of different organ/cancer-targeting agents utilizing the radiolabeling approaches described are provided.

Study of proton induced nuclear reactions on molybdenum: cross section measurements and theoretical calculations

Excitation functions were measured by the activation method using the stacked-foil technique for the natMo(p,x)93(m+g),94m,g,95m,g,96(m+g),99mTc, 92m,95Nb reactions up to 18 MeV. The experimental results were compared with literature data and theoretical results from EMPIRE-3.2.2 code and TENDL. Special attention was paid to the 100Mo(p,2n)99mTc reaction which is very promising for the production of 99mTc at a cyclotron. In order to optimize the production conditions of some medically important Tc isotopes, the integral yields were estimated based on the measured cross sections.

Production of novel diagnostic radionuclides in small medical cyclotrons

The global network of cyclotrons has expanded rapidly over the last decade. The bulk of its industrial potential is composed of small medical cyclotrons with a proton energy below 20 MeV for radionuclides production. This review focuses on the recent developments of novel medical radionuclides produced by cyclotrons in the energy range of 3 MeV to 20 MeV. The production of the following medical radionuclides will be described based on available literature sources: Tc-99 m, I-123, I-124, Zr-89, Cu-64, Ga-67, Ga-68, In-111, Y-86 and Sc-44. Remarkable developments in the production process have been observed in only some cases. More research is needed to make novel radionuclide cyclotron production available for the medical industry.

Isolation of high purity 73Se using solid phase extraction after selective 4,5-[73Se]benzopiazselenol formation with aminonaphthalene

A fast and efficient process for the production of the PET radionuclide 73Se was developed using 75Se as a surrogate. 75Se was separated from proton irradiated arsenic trioxide by reaction with 2,3-diaminonaphthalene to 4,5-[75Se]benzopiazelenol. This compound was purified using SPE column chromatography and subsequently decomposed with hydrogen peroxide. For further chemical conversions [75Se]selenite was reduced to elemental [75Se]selenium by either using thiosulfate or sulfur dioxide. The recovery yield of 75Se from the target amounted to 43%. The utility of the isolated 75Se for radiosyntheses was demonstrated by the successful preparation of [75Se]selenomethionine. The methodology developed using 75Se was successfully transformed to 73Se.

Development of novel radionuclides for medical applications

Medical radionuclide production technology is well established. There is, however, a constant need for further development of radionuclides. The present efforts are mainly devoted to nonstandard positron emitters (eg, ⁶⁴ Cu, ⁸⁶ Y, ¹²⁴ I, and ⁷³ Se) and novel therapeutic radionuclides emitting low-range β^- particles (eg, ⁶⁷ Cu and ¹⁸⁶ Re), conversion or Auger electrons (eg, ^117m Sn and ⁷⁷ Br), and α particles (eg, ²²⁵ Ac). A brief account of various aspects of development work (ie, nuclear data, targetry, chemical processing, and quality control) is given. For each radionuclide under consideration, the status of technology for clinical scale production is discussed. The increasing need of intermediate-energy multiple-particle accelerating cyclotrons is pointed out.

Measurements of excitation functions of α-particle induced reactions on natNi: possibility of production of the medical isotopes 61Cu and 67Cu

Excitation functions of the natNi(α,x)60,61Cu and 64Ni(α,p)67Cu reactions were measured using the stacked-foil activation technique. The experimental data achieved were compared with literature data as well as with nuclear model calculations performed using the code TALYS-1.8. Integral yields from the respective thresholds to 44 MeV were deduced from the measured excitation curves. The >99% pure 61Cu can be produced using the energy window of Eα=20→7 MeV, the yield amounting to 116 MBq/μAh. After a 2 h cooling time, the short-lived 60Cu (T1/2=23 min) impurity will be reduced to <0.1%. Due to low isotopic abundance of 64Ni, the enriched 64Ni target would be needed for the production of 67Cu via the (α,p) reaction. The cost would, however, be very high. In a few cases, particularly above 24 MeV, we have given new data points. In general, our measurements have strengthened the database.

Concurrent spectrometry of annihilation radiation and characteristic gamma-rays for activity assessment of selected positron emitters

A method is described to determine the activity of non-pure positron emitters in a radionuclide production environment by assessing the 511keV annihilation radiation concurrently with selected γ-lines, using a single High-Purity Germanium (HPGe) detector. Liquid sources of ²²Na, ⁵²Fe, ^52mMn, ⁶¹Cu, ⁶⁴Cu, ⁶⁵Zn, ⁶⁶Ga, ⁶⁸Ga, ⁸²Rb, ⁸⁸Y, ⁸⁹Zr and ¹³²Cs were prepared specifically for this study. Acrylic absorbers surrounding the sources ensured that the emitted β⁺-particles could not escape and annihilate away from the source region. The absorber thickness was matched to the maximum β⁺ energy for each radionuclide. The effect on the 511keV detection efficiency by the non-homogeneous distribution of annihilation sites inside the source and absorber materials was investigated by means of Monte Carlo simulations. It was found that no self-absorption corrections other than those implicit to the detector calibration procedure needed to be applied. The medically important radionuclide, ⁶⁴Cu, is of particular interest as its strongest characteristic γ-ray has an intensity of less than 0.5%. In spite of the weakness of its emission intensity, the 1346keV γ-line is shown to be suitable for quantifying the ⁶⁴Cu production yield after chemical separation from the target matrix has been performed.

The Beginning and Development of the Theranostic Approach in Nuclear Medicine, as Exemplified by the Radionuclide Pair 86Y and 90Y

In the context of radiopharmacy and molecular imaging, the concept of theranostics entails a therapy-accompanying diagnosis with the aim of a patient-specific treatment. Using the adequate diagnostic radiopharmaceutical, the disease and the state of the disease are verified for an individual patient. The other way around, it verifies that the radiopharmaceutical in hand represents a target-specific and selective molecule: the "best one" for that individual patient. Transforming diagnostic imaging into quantitative dosimetric information, the optimum radioactivity (expressed in maximum radiation dose to the target tissue and tolerable dose to healthy organs) of the adequate radiotherapeutical is applied to that individual patient. This theranostic approach in nuclear medicine is traced back to the first use of the radionuclide pair 86Y/90Y, which allowed a combination of PET and internal radiotherapy. Whereas the β-emitting therapeutic radionuclide 90Y (t½ = 2.7 d) had been available for a long time via the 90Sr/90Y generator system, the β⁺ emitter 86Y (t½ = 14.7 h) had to be developed for medical application. A brief outline of the various aspects of radiochemical and nuclear development work (nuclear data, cyclotron irradiation, chemical processing, quality control, etc.) is given. In parallel, the paper discusses the methodology introduced to quantify molecular imaging of 86Y-labelled compounds in terms of multiple and long-term PET recordings. It highlights the ultimate goal of radiotheranostics, namely to extract the radiation dose of the analogue 90Y-labelled compound in terms of mGy or mSv per MBq 90Y injected. Finally, the current and possible future development of theranostic approaches based on different PET and therapy nuclides is discussed.

Nuclear data for production and medical application of radionuclides: Present status and future needs

INTRODUCTION

The significance of nuclear data in the choice and medical application of a radionuclide is considered: the decay data determine its suitability for organ imaging or internal therapy and the reaction cross section data allow optimisation of its production route. A brief discussion of reaction cross sections and yields is given.

STANDARD RADIONUCLIDES

The standard SPECT, PET and therapeutic radionuclides are enumerated and their decay and production data are considered. The status of nuclear data is generally good. Some existing discrepancies are outlined. A few promising alternative production routes of ^99mTc and ⁶⁸Ga are discussed.

RESEARCH-ORIENTED RADIONUCLIDES

The increasing significance of non-standard positron emitters in organ imaging and of low-energy highly-ionizing radiation emitters in internal therapy is discussed, their nuclear data are considered and a brief review of their status is presented. Some other related nuclear data issues are also mentioned.

PRODUCTION OF RADIONUCLIDES USING NEWER TECHNOLOGIES

The data needs arising from new directions in radionuclide applications (multimode imaging, theranostic approach, radionanoparticles, etc.) are considered. The future needs of data associated with possible utilization of newer irradiation technologies (intermediate energy cyclotron, high-intensity photon accelerator, spallation neutron source, etc.) are outlined.

CONCLUSION

Except for a few small discrepancies, the available nuclear data are sufficient for routine production and application of radionuclides. Considerable data needs exist for developing novel radionuclides for applications. The developing future technologies for radionuclide production will demand further data-related activities.

[Disposal of radioactive contaminated waste from Ga-68-PET - calculation of a clearance level for Ge-68]

Ga-68-labeled radiotracers, particularly used for the detection of neuroendocrine tumors by means of Ga-68-DOTA-TATE or -DOTA-TOC or for the diagnosis of prostate cancer by means of Ga-68-labeled antigens (Ga 68-PSMA), become increasingly important. In addition to the high sensitivity and specificity of these radiopharmaceuticals, the short-lived radionuclide Ga-68 offers almost ideal nuclear characteristics for use in PET. Ga-68 is obtained from a germanium-gallium-generator system, so that the availability of Ga-68-labeled radiotracers is independent of an on-site-cyclotron regardless of the short half-life of Ga-68 of about 68minutes. Regarding the disposal of the radioactively contaminated waste from the preparation of the radiopharmaceutical, the eluted Ga-68 has to be considered to be additionally contaminated with its parent nuclide Ge-68. Due to this production-related impurity in combination with the short half-life of Ga-68, the radioactive waste has to be considered to be contaminated with Ge-68 and Ga-68 in radioactive equilibrium (hereafter referred to as Ge-68+). As there are no clearance levels for Ge-68+ given in the German Radiation Protection Ordinance, this work presents a method to calculate the missing value basing on a recommendation of the German Radiation Protection Commission in combination with simple geometric models of practical radiation protection. Regarding the relevant exposure scenarios, a limit value for the unrestricted clearance of Ge-68+ of 0.4 Bq/g was determined.

Uses of alpha particles, especially in nuclear reaction studies and medical radionuclide production

Alpha particles exhibit three important characteristics: scattering, ionisation and activation. This article briefly discusses those properties and outlines their major applications. Among others, α-particles are used in elemental analysis, investigation and improvement of materials properties, nuclear reaction studies and medical radionuclide production. The latter two topics, dealing with activation of target materials, are treated in some detail in this paper. Measurements of excitation functions of α-particle induced reactions shed some light on their reaction mechanisms, and studies of isomeric cross sections reveal the probability of population of high-spin nuclear levels. Regarding medical radionuclides, an overview is presented of the isotopes commonly produced using α-particle beams. Consideration is also given to some routes which could be potentially useful for production of a few other radionuclides. The significance of α-particle induced reactions to produce a few high-spin isomeric states, decaying by emission of low-energy conversion or Auger electrons, which are of interest in localized internal radiotherapy, is outlined. The α-particle beam, thus broadens the scope of nuclear chemistry research related to development of non-standard positron emitters and therapeutic radionuclides.

Evaluation of nuclear reaction cross sections for optimization of production of the emerging diagnostic radionuclide ⁵⁵Co

The excitation functions of the (54)Fe(d,n)(55)Co, (56)Fe(p,2n)(55)Co and (58)Ni(p,α)(55)Co reactions were analyzed with relevance to the production of the β(+)-emitter (55)Co (T½=17.53 h), a promising cobalt radionuclide for PET imaging. The nuclear model codes ALICE-IPPE, EMPIRE and TALYS were used to check the consistency of the experimental data. The statistically fitted excitation function was employed to calculate the integral yield of the product. The amounts of the radioactive impurities (56)Co and (57)Co were assessed. A comparison of the three investigated production routes is given.

Target development for diversified irradiations at a medical cyclotron

The irradiation facility at an old medical cyclotron (Ep=17 MeV; Ed=10 MeV) was upgraded by extending the beam line and incorporation of solid state targetry. Tests performed to check the quality of the available beam are outlined. Results on nuclear data measurements and improvement of radiochemical separations are described. Using solid targets, with the proton beam falling at a slanting angle of 20°, a few radionuclides, e.g. (75)Se, (120)I, (124)I, etc. were produced with medium currents (up to 20 µA) in no-carrier-added form in quantities sufficient for local use. The extended irradiation facility has considerably enhanced the utility of the medical cyclotron.

Activation cross-sections of proton induced reactions on natural Ni up to 65MeV

Production cross-sections of the (nat)Ni(p,x)(60,61)Cu, (56,57)Ni, (55,56,57,58)Co nuclear reactions were measured in five experiments up to 65MeV by using a stacked foil activation technique. The results were compared with the available literature values, predictions of the nuclear reaction model codes ALICE-IPPE, TALYS-1.4, and extracted data from the TENDL-2012 library. Spline fits were made on the basis of selected data, from which physical yields were calculated and compared with the literature values. The applicability of the (nat)Ni(p,x)(57)Ni, (57)Co reactions for thin layer activation (TLA) was investigated. The production rate for (55)Co was compared for proton and deuteron induced reactions on Ni.

The present and future of medical radionuclide production

Medical radionuclide production technology is well established. Both reactors and cyclotrons are utilized for production; the positron emitters, however, are produced exclusively using cyclotrons. A brief survey of the production methods of most commonly used diagnostic and therapeutic radionuclides is given. The emerging radionuclides are considered in more detail. They comprise novel positron emitters and therapeutic radionuclides emitting low-range electrons and α-particles. The possible alternative production routes of a few established radionuclides, like 68Ga and 99mTc, are discussed. The status of standardisation of production data of the commonly used as well as of some emerging radionuclides is briefly mentioned. Some notions on anticipated future trends in the production and application of radionuclides are considered.

Radiolabeling of Nanoparticles and Polymers for PET Imaging

Nanomedicine has become an emerging field in imaging and therapy of malignancies. Nanodimensional drug delivery systems have already been used in the clinic, as carriers for sensitive chemotherapeutics or highly toxic substances. In addition, those nanodimensional structures are further able to carry and deliver radionuclides. In the development process, non-invasive imaging by means of positron emission tomography (PET) represents an ideal tool for investigations of pharmacological profiles and to find the optimal nanodimensional architecture of the aimed-at drug delivery system. Furthermore, in a personalized therapy approach, molecular imaging modalities are essential for patient screening/selection and monitoring. Hence, labeling methods for potential drug delivery systems are an indispensable need to provide the radiolabeled analog. In this review, we describe and discuss various approaches and methods for the labeling of potential drug delivery systems using positron emitters.