Method for producing Ac-225 by irradiation of Ra-226 with...

Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal

Reexamination Certificate

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C376S125000

Reexamination Certificate

active

06299666

ABSTRACT:

The invention refers to a method for producing Ac-225, comprising the steps of preparing a target containing Ra-226, of irradiating this target with protons in a cyclo-tron and of chemically separating Ac from the irradiated target material. Such a method is known for example from EP-A-0 752 709.
According to this document the protons are accelerated in a cyclotron and are projected onto a target containing Ra-226 so that unstable radionuclei are transformed into Actinium by emitting neutrons. The possible nuclear reactions lead among others to Ac-226, Ac-225 and Ac-224.
Radio-immunotherapeutic methods for locally attacking cancer disease (metastases) become more and more important in view of progresses in immunology and radiotherapy and in the molecular biology field. Generally speaking, short half-life alpha-emitting nuclides are conjugated to a carrier (e.g. monoclonal antibodies) which after having been introduced into the patient body tend to be linked to and be integrated into malign cells and to destroy these cells due to an intense irradiation of very short range. The radionuclide must in this case cope with particular requirements: It must be apt to be linked for conjugation to a convenient antibody, it must have a convenient half-life and it should be readily available.
Among the possible candidates for such a radionuclide, Ac-225 and its daughter Bismuth-213 are preferred for radio-immunotherapy purposes (see for example EP-B-0 473 479). In the above cited document EP-A-0 752 709 it is described that the irradiation of Ra-226 by a proton beam results in the desired Ac-225 but also in considerable quantities of other highly undesired radionuclides, especially Ac-224 and Ac-226. In order to eliminate these undesired radionuclides said document suggests to delay the post-irradiation processing since the undesired nuclides cited above present a fairly short half-life compared with Ac-225 (half-life 10 days). Nevertheless this waiting period also leads to a considerable loss of Ac-225.
The invention proposes a method allowing to reduce or even eliminate this waiting period by a method supplying a higher yield and purity of the produced Ac-225. A further object of the invention is to produce Ac-225 by observing the safety regulations for handling the basic very radiotoxic material Ra-226 and the purity specifications of Ac-225 as required for the therapeutic use.
These objects are achieved by the method as claimed in claim
1
. It has been found that the highest purity is achieved at an intermediate value of the proton impact energy of about 15 Mev.
Further improvements of the method as far as the preparation of the target, its irradiation and its final processing is concerned, are specified in the secondary claims.


REFERENCES:
patent: 4088532 (1978-05-01), Blue
patent: 5355394 (1994-10-01), van Geel et al.
patent: 5885465 (1999-03-01), Bray et al.
patent: 0 752 709 (1997-01-01), None
Qaim, S.M., Target Development for Medical Radioisotope Production at a Cyclotron, INTDS & IAEA-INDC Conference on Heavy-Ion Targets and Related Phenomena, Darmstada, West Germany Sep. 5-9, 1988, vol. A282, No. 1, pp. 289-295.
XP000067681, Nuclear Instruments & Methods in Physics Research, Section A, Accelerators, Spectrometers, Detectors, and Associated Equipment), Oct. 1, 1989, Netherlands, p. 293, ¶3.3; figure 3.
Colmar, D., et al.,Biomedical Cyclotrons for Radioisotope Production, Nuclear Medicine and Biology, vol. 13, No. 2, 1986, pp. 101-107.
Mausner L.F., et al., The Production of Spallation Radionuclides for Medical Applications at BLIP, 1982 IEEE Conference on the Application of Accelerators in Research and Industry, Denton, Texas, USA, Nov. 8-10, 1982, vol. 30, No. 2, pp. 1793-1796.
Database WPI, Section Ch. Week 9417, Derwent Publications Ltd., London GB; Class A14, AN 94-142414.

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