Stefan Spellerberg

PET quantitation and imaging of the non-pure positron-emitting iodine isotope 124I.

A series of PET studies using phantoms is presented to characterize the imaging and quantitative performance of the positron-emitting iodine isotope 124I. Measurements were performed on the 2D-PET scanner GE 4096+ as well as on the Siemens PET scanner HRR+ operated in both 2D and 3D modes. No specific correction was applied for the gamma-rays emitted together with the positrons. As compared to 18F, in studies with 124I there is a small loss of image resolution and contrast, and an increase in background. The quantitative results varied between different scanners and various acquisition as well as reconstruction modes, with an average relative difference of -6 +/- 13% (mean+/-SD) in respect of the phantom radioactivity as measured with gamma-ray spectroscopy. We conclude that quantitation of a radiopharmaceutical labelled with 124I is feasible and may be improved by the development of specific corrections.

Some optimisation studies relevant to the production of high-purity 124I and 120gI at a small-sized cyclotron

Optimisation experiments on the production of the positron emitting radionuclides 124I(T(1/2) = 4.18d) and (120g)I (T(1/2) = 1.35 h) were carried out. The TeO(2)-target technology and dry distillation method of radioiodine separation were used. The removal of radioiodine was studied as a function of time and the loss of TeO(2) from the target as a function of oven temperature and time of distillation. A distillation time of 15 min at 750 degrees C was found to be ideal. Using a very pure source and comparing the intensities of the annihilation and X-ray radiation, a value of 22.0 +/- 0.5% for the beta(+) branching in 124I was obtained. Production of 124I was done using 200 mg/cm(2) targets of 99.8% enriched 124TeO(2) on Pt-backing, 16 MeV proton beam intensities of 10 microA, and irradiation times of about 8 h. The average yield of 124I at EOB was 470 MBq(12.7 mCi). At the time of application (about 70 h after EOB) the radionuclidic impurity 123I (T(1/2) = 13.2 h) was <1%. The levels of other impurities were negligible (126I < 0.0001%;125I = 0.01%). Special care was taken to determine the 125I impurity. For the production of (120g)I only a thin 30 mg target (on 0.5 cm(2) area) of 99.9% enriched 120TeO(2) was available. Irradiations were done with 16 MeV protons for 80 min at beam currents of 7 microA. The 120gI yield achieved at EOB was 700 MBq(19 mCi), and the only impurity detected was the isomeric state 120 mI(T(1/2) = 53 min) at a level of 4.0%. The radiochemical purity of both 124I and 120gI was checked via HPLC and TLC. The radioiodine collected in 0.02 M NaOH solution existed >98% as iodide. The amount of inactive Te found in radioiodine was <1 microg. High purity 124I and 120gI can thus be advantageously produced on a medium scale using the low-energy (p,n) reaction at a small-sized cyclotron.

Radiochemical studies relevant to the production of 86Y and 88Y at a small-sized cyclotron

Summary Excitation functions were measured by the stacked–foil technique for natSr(p, xn)88,87m,gY reactions from threshold up to 25 MeV. From the measured cross sections integral yields of 88Y, 87mY and 87gY were calculated. The optimum energy range for the production of 88Y is Ep = 14 → 9 MeV; the 88Y yield amounts to 1.75 MBq (47.3 µCi/µA·h) and the 87Y and 87mY impurities to 2.0 and 4.4%, respectively. The isomeric cross section ratio for the pair 87m,gY was determined as a function of incident proton energy and the results are discussed in terms of the spins of the two isomeric states involved. Medium scale production of both 86Y and 88Y has been carried out more than 15 times each using the (p, n) reaction. In the former case 96.3% enriched 86SrCO3 was used as target material, and in the latter natSrCO3. The method of separation of radioyttrium has been improved. After coprecipitation with La(OH)3, cation–exchange HPLC was applied to isolate radioyttrium from the carrier lanthanum. The radionuclidic and chemical purities of the products were good. Batch yields of 86Y and 88Y amounted to about 3.5 GBq and 35 MBq, respectively.

Production of 55Co and 57Co via proton induced reactions on highly enriched 58Ni

Abstract 55Co and 57Co were produced via (p, α) and (p, 2p) reactions, respectively, on highly enriched 58Ni. Thin deposits of 58Ni on Cu backing, obtained electrolytically, were irradiated using a slanting beam. The separation of radiocobalt and the recovery of the enriched target material were effected via anion-exchange chromatography.

Experimental determination of proton induced reaction cross sections on natNi near threshold energy

Abstract A newly developed facility at the 3 MV Tandem Accelerator at Dhaka for measurement of proton induced reaction cross sections in the energy region below 5 MeV is outlined and tests for the beam characterization are described. The results were validated by comparison with the well-known excitation function of the 64Ni(p, n)64Cu reaction. Excitation functions of the reactions natNi(p, x)60,61Cu, natNi(p, x)55,57,58m+gCo and natNi(p, x)57Ni were also measured from threshold to 16 MeV using the stacked-foil technique, whereby irradiations were performed with 5 MeV protons available at the Tandem Accelerator and 16.7 MeV protons at the BC 1710 cyclotron at Jülich, Germany. The radioactivity was measured using HPGe γ-ray detectors. A few results are new, the others strengthen the database. In particular, the results of the reaction natNi(p, x)61Cu below 3 MeV could serve as beam monitor.

New cross section measurements for the production of the Auger electron emitters 77Br and 80mBr

Abstract The two Auger electron emitting radionuclides of bromine, namely 77Br (T1/2=57.04 h) and 80mBr (T1/2=4.4 h), are promising candidates for internal radiotherapy. In this work, nuclear reaction cross sections were determined for their production using enriched Se targets. Thin Se samples were irradiated with incident protons of energies up to 85 MeV and the induced radioactivity was measured via non-destructive γ-ray spectroscopy, allowing the determination and extension of the excitation functions of the four reactions 77,78,80Se(p,ߙxn) 77Br and 80Se(p,ߙn)80mBr. The possible thick target yields were calculated and the different production routes discussed, especially with regard to the yield and the radionuclidic purity of the produced radionuclides.

Production of no-carrier-added radiobromine: new nickel selenide target and optimized separation by dry distillation

Abstract Nickel(II) selenide (NiSe) was investigated as a new high-current target material for cyclotron production of radiobromine, as it contains a higher amount of selenium and has a lower melting point than the widely used Cu2Se. Using a slanted target system, NiSe was successfully tested up to beam currents of 16 μA so far. With regard to the isolation of no-carrier-added (n.c.a.) radiobromide from the target material, an improved dry distillation device with high yields of 76% – 86% was developed. The implementation of a special custom-made quartz funnel decreased the dead volume of the apparatus and a quartz capillary for trapping the radiobromine allowed to concentrate the radioactivity in a small volume of less than 100 μL of 0.1 M NaOH, ready for immediate subsequent radiosyntheses. Thus, the new apparatus improves the handling of the isolation procedure and the radioactive product. The radiochemical purity of the resulting solution of n.c.a. [*Br]bromide was verified by radio-IC where no other species were detected.

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.

Ion-exchange separation of radioiodine and its application to production of 124I by alpha particle induced reactions on antimony

Abstract The basic parameters related to radiochemical separation of iodine from tellurium and antimony by anion-exchange chromatography using the resin Amberlyst A26 were studied. The separation yield of 124I amounted to 96% and the decontamination factor from 121Te and 122Sb was > 104. The method was applied to the production of 124I via the 123Sb(α, 3n) reaction. In an irradiation of 110 mg of natSb2O3 (thickness ∼ 0.08 g/cm2) with 38 MeV α-particles at 1.2 μA beam current for 4 h, corresponding to the beam energy range of Eα = 37 → 27 MeV, the batch yield of 124I obtained was 12.42 MBq and the 125I and 126I impurities amounted to 3.8% and 0.7%, respectively. The experimental batch yield of 124I amounted to 80% of the theoretically calculated value but the level of the radionuclidic impurities were in agreement with the theoretical values. About 96% of the radioiodine was in the form of iodide and the inactive impurities (Te, Sb, Sn) were below the permissible level. Due to the relatively high level of radionuclidic impurity the 124I produced would possibly be useful only for restricted local consumption or for animal experiments.

Small scale production of high purity 193mPt by the 192Os(α,ߙ3n)-process

Abstract Some production aspects of the Auger electron emitter 193mPt (T1/2=4.33 d) through the 192Os(α,ߙ3n)-process were investigated. Relatively thick targets of 99.65% enriched 192Os, prepared by pressing or electrolytic deposition, were irradiated with 40 MeV α-particles for 3 h at a nominal beam current of 1.6 μA. The radioplatinum formed was chemically separated with a yield of 90% and the expensive target material was recovered with a yield of 85%. The radioactivity of 193mPt was determined by high resolution X-ray spectrometry. The radionuclidic purity of 193mPt amounted to 99%, the level of 195mPt and 191Pt impurities being each 0.5%. The batch yield of 193mPt achieved was about 10 MBq with a specific activity of 1 GBq/μg Pt. Both the batch yield and the specific activity could be appreciably increased through improved targetry. A comparison of the cyclotron and reactor production routes of 193mPt shows that the (n,ߙγ) reaction leads to high production yields but the α-particle induced reaction results in a product of higher radionuclidic purity and four orders of magnitude higher specific activity of 193mPt.