PRODUCTION OF HIGHLY PURIFIED 212PB

Abstract

The present invention relates to assemblies and method for obtaining a container comprising .sup.212Pb on the walls obtained from a .sup.212Pb precursor isotope source. The invention provides an improved system and method for producing .sup.212Pb high purity without the need for processing, with high yields, and which safely and efficiently can be transported to the locations where it is to be used.

Claims

1. A method for obtaining a container comprising .sup.212Pb on the walls comprising the steps of: providing an assembly comprising a first part and a second part, wherein the first part comprises a container and the second part comprises a .sup.212Pb precursor isotope source, connecting the first part and the second part such that the .sup.212Pb precursor isotope source does not come into contact with an inner wall of the container and such that a single chamber container assembly is provided, allowing the .sup.212Pb precursor isotope source sufficient time to decay to progenies .sup.220Rn, .sup.216Po, and/or .sup.212Pb, and sufficient time for .sup.220Rn, .sup.216Po and/or .sup.212Pb to settle onto the inner walls of the single chamber container assembly, removing or isolating the remaining .sup.212Pb precursor isotope from the single chamber assembly without having the .sup.212Pb precursor isotope source come into contact with an inner wall of the single chamber container assembly, and obtaining a container comprising .sup.212Pb on an inner wall of the container and being substantially free of the .sup.212Pb precursor isotope source on the inner wall of the container.

2-38. (canceled)

39. An assembly comprising a first part and a second part, wherein the first part comprises a container and the second part comprises a .sup.212Pb precursor isotope source, wherein the first part and the second part are connected such that the .sup.212Pb precursor isotope source does not come into contact with an inner wall of the container, and such that a single chamber container assembly is provided.

40. A single chamber container assembly comprising a first part and a second part, wherein the first part comprises a container and the second part comprises a .sup.212Pb precursor isotope source, wherein the first part and the second part are connected such that the .sup.212Pb precursor isotope source does not come into contact with an inner wall of the container.

41. The method according to claim 1, wherein the single chamber container assembly is gas tight.

42. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is selected from the group consisting of .sup.232Th, .sup.228Ra, .sup.228Ac, .sup.228Th and .sup.224Ra.

43. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is a mixture of .sup.232Th, .sup.228Ra, .sup.228Ac, .sup.228Th and .sup.224Ra.

44. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is a mixture of .sup.228Th and .sup.224Ra.

45. The method according to claim 1, wherein the .sup.212Pb activity is 0% to 114% of the .sup.224Ra precursor activity.

46. The method according to claim 1, wherein the .sup.212Pb activity is 0% to 103% of the .sup.228Th precursor activity.

47. The method according to claim 1, wherein the total amount of radioactivity in the single chamber container assembly is 1 kBq-100 GBq.

48. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is in the form of an inorganic or organic salt.

49. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is bound to a non-radioactive material.

50. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is in a dry form or in a liquid solution.

51. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is in a liquid solution that is at acidic, neutral or basic pH.

52. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is deposited on a sponge, a wool, a strip or a sphere that is made of a material suitable for application of a liquid.

53. The method according to claim 1, wherein the .sup.212Pb precursor isotope source is deposited on a sponge, a wool, a strip or a sphere, which is made of material that is selected from the group consisting of quartz, glass, mineral, paper, plastic, metal, ceramic, natural fibres and synthetic fibres.

54. The method according to claim 53, wherein a strip or sphere is attached to the second part, which comprises a holder configured to retain the sponge, the wool, the strip or the sphere.

55. The method according to claim 54, wherein the second part comprises a syringe, or wherein the holder is a syringe.

56. The method according to claim 55, wherein the tip of the syringe has been pushed through a rubber cap.

57. The method according to claim 1, wherein the second part comprises a rod that is attached to the closure of the container.

58. The method according to claim 57, wherein the closure for the container is a cap, cover or a lid.

59. The method according to claim 58, wherein the cap, cover or a lid is made of a material selected from the group consisting of quartz, glass, mineral, rubber, glass, paper, plastic, metal, ceramic, natural fibres or synthetic fibres.

60. The method according to claim 59, wherein the .sup.212Pb precursor isotope source is placed on or in a sphere, configured to hold the source but allow radon diffusion.

61. The method according to claim 1, wherein the container comprises a gas permeable barrier impervious to the .sup.212Pb precursor isotope source.

62. The method according to claim 61, wherein the gas permeable barrier impervious to the .sup.212Pb precursor isotope source is in contact with the .sup.212Pb precursor isotope source.

63. The method according to claim 1, wherein the container does not comprise a gas permeable barrier impervious to the .sup.212Pb precursor isotope source.

64. The method according to claim 1, wherein volume of the container is 1 μl to 10 litres.

65. The method according to claim 1, wherein the amount of .sup.212Pb precursor isotope source on the inner wall of the container is less than 3% .sup.224Ra of the .sup.212Pb precursor isotope source as measured as % relative radioactivity.

66. The method according to claim 1, wherein the inner walls of the container are coated.

67. The method according to claim 1, wherein the inner walls of the container are coated with a compound that comprises a chelator which can complex with .sup.212Pb.

68. The method according to claim 1, wherein the inner walls of the container are coated with a chelator, which is TCMC or a variant hereof.

69. The method according to claim 1, wherein the container comprises an aqueous or an oil solution.

70. The method according to claim 1, wherein the second part of the assembly comprises a piston that can be in open and closed positions.

71. The method according to claim 1, wherein the second part of the assembly comprises a chamber with a gas tight o-ring seal.

72. The method according to claim 1, wherein the second part of the assembly comprises a gas and liquid tight lid or valve.

73. The method according to claim 1, wherein the assembly is made by a glass flask placed up-side down and with quartz wool with .sup.224Ra or .sup.228Th placed in the centre of the inside of the cap.

74. A method of obtaining a .sup.212Pb solution comprising obtaining a container or assembly comprising .sup.212Pb on the walls according to claim 1, and subsequently collect the .sup.212Pb in a solution.

75. A method of obtaining a .sup.212Pb solution comprising obtaining a glass flask assembly according to claim 73, unscrewing the flask standing up-side down from the cap with the source, and thereafter washing the interior of the flask with a solution to dissolve .sup.212Pb.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0091] FIG. 1 shows the decay of .sup.232Th to its progenies. The decay type (alpha or beta) is indicated and so is the half-lives. These half-lives are important because they dictate the decay rate and are therefore also key in deciding the optimal mix of isotopes as .sup.212Pb precursor isotope source for the production of .sup.212Pb.

[0092] FIG. 2A shows a figure of the single chamber container assembly with the container (A), the a .sup.212Pb precursor isotope source (B) that generates the .sup.220Rn gas which is released into the single chamber container assembly and after decay settled as .sup.212Pb onto the inner walls of the container (C). The upper part of the single chamber container assembly (D) is the second part which comprises the .sup.212Pb precursor isotope source and in this case a cover/cap with a rod attached pointing towards the centre of the container thus enabling .sup.212Pb precursor isotope source release of .sup.220Rn into the container. FIG. 2B shows a situation where the .sup.212Pb precursor isotope source (B) has been withdrawn into a gas tight seal that ensures that no .sup.220Rn is released into the container. The .sup.212Pb precursor isotope source can also be removed entirely from the assembly.

[0093] FIG. 3 shows picture of a crude version of the generator system based on a 3 ml v-vial with an membrane inserted open top screw cap penetrated by a syringe tip (with position fixed by tape on top of screw cap) and with a strip of laboratory bench paper attached to the syringe tip (left picture shows the .sup.212Pb precursor isotope source and container). The .sup.212Pb precursor isotope source is placed onto the strip by a pipette before the screwcap with the source is carefully attached to the vial (right picture). It is very important that the source is not touching the vial when assembling and disassembling the unit to avoid cross-contamination.

[0094] FIG. 4. An example of a single chamber diffusion generator for .sup.212Pb with a retractable source simplifying washout of .sup.212Pb from the inner surfaces by having syringe permeable zones on the lid supplied with septum, a syringe could be used for washing of the interior surfaces without radionuclide cross contamination when the unit is put in closed position.

[0095] FIG. 5. Top picture shows a 100, 50 and 10 ml generator unit for .sup.212Pb production. Bottom pictures shows the cap with quartz wool in the center of the inner surface. The .sup.212Pb precursor nuclide solution can be placed onto the quartz wool and the flask mounted for up-side-down storage to produce .sup.212Pb deposited on the flask' inner surface generated via .sup.220Rn diffusion from the precursor source material.

EXAMPLES

Example 1—Calculation of the Relative .SUP.212.Pb Daughter Nuclide Level at Various Time Points

[0096] Background. The development and use of pure .sup.212Pb in therapeutic radiopharmaceuticals is hampered by the short half-life (10.6 h) of the radionuclide making it almost impossible to produce a product in a centralized fashion and shipped to the end user. If .sup.224Ra is used as a short-term generator for .sup.212Pb the level of .sup.212Pb activity can be maintained essentially according to the half-life of .sup.224Ra, which is 3.6 days. The variation in .sup.212Pb level in a sealed source of pure .sup.224Ra is shown.

[0097] Method: The ingrowth of .sup.212Pb from a pure .sup.224Ra source were calculated using a universal activity calculator.

[0098] Results: Table 2 shows the amount of .sup.212Pb at various time points after the production of a pure (.sup.224Ra-free) pharmaceutical solution and storage in a gas tight container. As can be seen the pure .sup.212Pb source rapidly decays and lose more than 75% per 24 h. Table 3 shows the amount of .sup.212Pb present in a sealed source of .sup.224Ra at the same time points. As can be seen the .sup.212Pb activity is maintained at a high level (>50%) at least up to 96 h.

[0099] Table 4 shows the effect of “milking” a .sup.224Ra precursor-based generator for .sup.212Pb several times during a 96-h period.

[0100] The data also shows that significant amount of daughter nuclide is present within a relatively short time frame when starting with pure .sup.224Ra. It is noteworthy though that the ratio of .sup.212Pb to .sup.224Ra in the solution reaches 1 after 36 hours and thereafter gradually increases to about 1.1 of which is kept for the rest of the time until complete decay. In conclusion, using .sup.224Ra as a source for .sup.212Pb makes the logistic of centralized production and shipment to end users possible providing an easy way to extract the .sup.212Pb from .sup.224Ra exist.

Example 2—Preparation of Radionuclides and Counting of Radioactive Samples

[0101] In the following, all work with the concentrated radioactive preparations including evaporation of solvent etc was performed in a glove-box. A source of .sup.228Th in 1 M HNO3 was acquired from a commercial supplier. Ac-resin was obtained from Eichrom Technologies LLC (Lisle, Ill., USA) in the form of a pre-packed cartridge.

[0102] Radium-224 was made from .sup.228Th bound to Actinide resin (Eichrom Technologies, LLC) by eluting a column containing actinide resin with immobilized .sup.228Th with 1 M HCl. The eluate was purified on a second Ac-resin column and the eluate evaporated to dryness using an evaporation vial with a cap with gas inlet and outlet placed in a heater block at approximately 110° C. and a gentle stream of nitrogen gas to evaporate of the solvent. When the evaporation vial was empty from solvent it was added 0.1 M HCl to dissolve the residue, typically 200-400 μl. Typically, more than 70% of the .sup.224Ra present in the .sup.228Th source could be extracted and purified using the described methods.

[0103] Radioactive samples were counted on a Cobra II Autogamma counter (Packard Instruments, Downer Grove, Ill., USA). During extraction of .sup.224Ra from the .sup.228Th source, a CRC-25R dose calibrator (Capintec Inc., Ramsey, N.J., USA) was used.

Example 3—Determining Net Count Rate for .SUP.212.Pb in a .SUP.212.Pb/.SUP.224.Ra Mixture Before Radioactive Equilibrium has Been Reached

[0104] After more than 3 days, i.e., “equilibrium” a sample kept gas tight will for practical purposes have 1.1 times .sup.212Pb vs .sup.224Ra.

[0105] In a gas tight unit regardless of whether .sup.212Pb is at or lower than equilibrium it can be assumed that this is reached after 3 days since surplus .sup.212Pb is reduced by 99% and the ingrowth of .sup.212Pb from .sup.224Ra is practically complete vs. “equilibrium”.

[0106] Using the Cobra II Autogamma counter with a counting window setting from 70-80 KeV gives mainly the .sup.212Pb with very little contribution from other radionuclides in the .sup.224Ra series. Radium-224 must be indirectly counted when the initial .sup.212Pb has vanished and equilibrium between .sup.224Ra and .sup.212Pb has been reached (after approximately 3 days). This indirect counting requires the sample to be stored in a relatively gas tight containers as otherwise the .sup.220Rn may escape preventing the radionuclide equilibrium of 1.1 between .sup.212Pb and .sup.224Ra to be reached.

[0107] Since sampling and counting may be separated by some time, the net count rate for .sup.212Pb can be adjusted for decay to determine the net .sup.212Pb count rate at the time of sampling. By storing .sup.212Pb samples for a week or longer and remeasure, the amount of .sup.224Ra contaminant can be determined as activity after about 110 hours of storage would not be .sup.212Pb but must be from longer lived precursor isotope.

Example 4—A Simplified Single Chamber (Diffusion Chamber Generator) Assembly for .SUP.212.Pb Production (FIG. 3)

[0108] A 3 ml v-vial with an open top cap. The open top cap was supplied with a membrane permeable by a syringe tip. A syringe tip was pushed through the membrane and fixed with tape on top to lock the position of the tip with regard to the open top cap. On the syringe tip vas placed a strip of absorbent paper about 0.5×3 cm by inserting the syringe tip in two holes in the strip. The paper strip was added 2-40 ul .sup.224Ra solution. Thereafter the cap was placed carefully onto the v-vial while the syringe tip and radioactive strip were not to touch the inside of the v-vial. Thereafter the assembly was standing for various time to produce .sup.212Pb via .sup.220Rn diffusion from the strip to the space surrounding the strip. The .sup.212Pb tended to settle on the inner surfaces of the v-vial. Depending on the liquid volumes used for applying the .sup.224Ra source onto the strip, there may be some condensation of liquid due to evaporation/condensation of the liquid applied. Alternatively, the source could be dried before assembling the unit to avoid any solvent condensation on the v-vial inner surfaces.

Example 5A:

[0109] Production of .sup.212Pb with the .sup.212Pb precursor isotope source absorbed on a paper strip.

[0110] Methods: The assembly was assembled with .sup.224Ra placed on the strip of the diffusion subunit inserted in a v-vial according to FIG. 3, and was standing for 17.5 h or more to produce .sup.220Rn and .sup.212Pb. Production of .sup.212Pb evaluation of radiochemical purity of product. At the end of the production period the whole unit was measured on a Capintec dose calibrator. The product was evaluated by separating the source from the container and cap the latter with a gas tight screw cap and measure immediately in the Capintec dose calibrator. The purity of the product was determined by measuring the collector subunit again after a few days when all the .sup.212Pb had decayed but the presence of longer-lived predecessor nuclides .sup.224Ra and .sup.228Th would have been measurable. Results: Highly purified .sup.212Pb was collected in the collector subunit with a relevant yield of 65.6% (range 62.7-69.9% n=4) and with no measurable longer-lived precursor nuclides present (<0.5%). In conclusion: The assembly was effective in producing and collecting purified .sup.212Pb in an easy manner without need for further purification.

Example 5B:

[0111] Production of .sup.212Pb with the .sup.212Pb precursor isotope source absorbed on a parafilm strip. The experiment from 5A was repeated except that a parafilm strip was used instead of paper a strip to carry the precursor isotope source.

[0112] Results: The yield of .sup.212Pb on the inner surfaces of the collector subunit (vial or container) was found to be only 19.3%. In contrast a unit with paper strip run in parallel with exact same configuration and emanation period gave a yield of 63.9%. In conclusion, the material used for absorbing and holding the .sup.212Pb precursor isotope source could greatly affect the yield of .sup.212Pb on the collector subunit or container.

Example 6: Dissolving of .SUP.212.Pb from the Container Using a Solution

[0113] Methods: The collector vial was added 0.3-0.5 ml 0.1 M HCl which was gently swirled to contact the inner surfaces with the liquid and counted in the Capintec dose calibrator. Thereafter the liquid was transferred to an Eppendorf tube and measured in the Capitec dose calibrator. The extraction yield was 74.0% (range 70.0-76.9%, n=3) when the collector subunit (3 ml v-vial), was washed one single time with 0.3 ml 0.1 M HCl. In conclusion, .sup.212Pb absorbed onto the surfaces of the container was rapidly and with good yield dissolved by a solution useful for radiopharmaceutical processing.

Example 7: Thin Layer Chromatography Analyses

[0114] Thin layer chromatography (TLC) was performed using chromatography strips (model #150-772, Biodex Medical Systems Inc, Shirley, N.Y., USA). A small beaker with about 0.5 ml of 0.9% NaCl was used to place strips with a sample spot in. To the strip was typically added 1-4 μl of sample at approximately 10% above the bottom of the strip. After the solvent front had moved to about 20% from the top of the strip, the strip was cut in half and each half was placed in a 5 ml test tube for counting. In this system radiolabeled antibody and free radionuclide does not migrate from the bottom half while radionuclide complexed with EDTA migrates to the upper half. A formulation buffer (FB) consisting of 7.5% human serum albumin and 1 mM EDTA in DPBS and adjusted to approximately pH 7 with NaOH was mixed with the radioconjugates in ratio 2:1 for at least 5 minutes before application to the strips to determine free radionuclide. It was verified that in a test solution with free .sup.212Pb was the radionuclide was completely (>99%) complexed by the EDTA, when mixed with FB, and would travel to the upper half of the TLC strip.

Example 8: In Situ Chelation of .SUP.212.Pb in Solutions

[0115] Background: The labeling properties of the .sup.212Pb extracted with 0.1 M HCl from the containers was evaluated. Methods: A 10:1 ratio of .sup.212Pb in 0.1 M HCl and 5 M ammonium acetate was used before addition of the chelators, resulting in a pH range of 5-6 for the reactions. Reaction times of 15-30 minutes at 37° C., were tested. For PSMA-617 solutions of 5 μg per 100 μl was labeled with good yield of 96.6% as determined by TLC. Also, TCMC-conjugated Herceptin antibody solution of approximately 1.0 mg/ml was labeled with pure .sup.212Pb with a good yield of 98.9%. In conclusion: Lead-212 produced with the assembly was readily complexed with small molecular and large molecular conjugates indicating suitability for use in production of .sup.212Pb based radiopharmaceuticals.

Example 9—Production of .SUP.212.Pb from the .SUP.224.Ra Source when Unit is Kept Sealed and Emptied Only at One Time Point

[0116] Table 3, lower row, shows the example of an output from a diffusion generator emptied after various time points after insertion of the source of 100 MBq of .sup.224Ra into the unit. As shown the generator gives a relatively stable output of .sup.212Pb for up to 96 h.

Example 10—Production of .SUP.212.Pb from the .SUP.224.Ra Source when Unit is Emptied Once a Day for Four Days e.g. if Used for Fractionated Radionuclide Therapy Etc

[0117] Table 4 shows the output when the assembly is “milked” once every 24 h. The combined output is a total of 151.5 MBq of .sup.212Pb when starting with a 100 MBq source. In conclusion, the one chamber assembly is suitable for single dose as well as fractionated dose production.

Example 11—Example of an Assembly with a Retractable Source (FIG. 2 and FIG. 4)

[0118] The materials used may be of glass (including quartz), polymer, metal, ceramic or other suitable materials for pharmaceutical containers. The rod in FIG. 2 (piston in FIG. 4) slides in a tube with o rings or similar at the top to secure gas tight seal. The valve at the bottom of the rod is gas and liquid tight in the closed position for the unit.

[0119] In the open position the source will be exposed inside the container and emanate .sup.220Rn and cause deposit of .sup.212Pb onto the inner surface. In closed position the source is sealed off from the container (FIG. 2B) and the container surfaces can be contacted with a suitable solution to dissolve .sup.212Pb.

[0120] In one embodiment where the cap has syringe permeable membrane, a sterile syringe with a sterile solution is used to extract the .sup.212Pb without removing the cap. When such unit has been autoclaved before the extraction of .sup.212Pb, the complete procedure can be performed in an aseptic/sterile fashion.

Example 12. Precursor Nuclide Placed onto Quartz Wool in a .SUP.212.Pb Single Chamber Generator

[0121] Methods: A flasks as shown in FIG. 5, was used. Flask size could vary and typically 10-100 ml flasks were used. When used as a generator the flask was turned-up-side down. The cap was removed and inside of the center of the cap was placed quarts or glass wool. Radium-224 in solution was placed on the quartz wool and the flask was mounted onto the cap without touching the quartz wool with the flask. The unit was kept tight and stored in up-side-down position for a period of time to produce .sup.212Pb from ingrowth. After typical one to a few days the flask was unscrewed from the cap while being held up-side-down and carefully removed from the cap without touching the quartz wool. The cap with the source was combined with another flask and stored up side down for further .sup.212Pb production. The unscrewed .sup.212Pb containing flask was added a solution of 0.5-2 ml of 0.1 M HCl and the .sup.212Pb extracted from the flask by washing the interior surfaces and collected for use.

[0122] Results: Typically, 50-70 percent of the .sup.212Pb activity produced was found in the flask and by carefully washing more than 90% of the .sup.212Pb activity could be collected in the washing solution. The produced .sup.212Pb had a very high purity with .sup.224Ra being as low as 10.sup.−4 vs .sup.212Pb in newly extracted solutions. The product was very suitable for use in labeling of chelator-containing proteins and small molecules giving very high labeling yields, typically above 97%.

[0123] In conclusion, the data showed that quartz wool was very suitable for holding a .sup.224Ra source indicating that quartz/glass/mineral wool, metal wool etc would be suitable for this purpose. It would be possible to use the flask/quartz wool system in upright position also providing the quartz wool is adhered to the capsule, e.g. with glue, double-sided mounting tape etc. In the current example the flask was used up-side down and the quartz wool was not adhered, but just placed and kept by gravity in position inside the cap.

Example 13. Up-Side-Down Flask System Version of Single the Chamber Generator

[0124] Flask based diffusion generator for labeling with .sup.212Pb.

[0125] Lead-212 generate therapeutic high-LET radiation as it decays via short-lived alpha emitting daughters resulting in an average of one alpha particle per .sup.212Pb decay. The half-life of .sup.212Pb of 10.6 hours is a limitation to its use and fast and safe production and purification procedures are required. If a ready to use product was to be produced in a centralized production facility and shipped to the end user, the activity level would be reduced to less than 25% in one day. Lead-212 based radioimmunoconjugate has been in clinical testing against peritoneal cancer using .sup.212Pb separated from .sup.224Ra in a cation exchange column and eluted in mineral acid which has to be reconstituted before radiolabeling. This method requires a significant work effort, facilities, and equipment suitable for evaporation of mineral acids etc to work up the .sup.212Pb from the .sup.224Ra generator material. An alternative generator method was developed and tested based on .sup.224Ra absorbed onto quartz wool and placed inside the centered ring of a removable cap (the generator cap), in a generator chamber. The chamber consists of a glass bottle turned upside down and the removable cap supports the .sup.224Ra labeled quartz wool (FIG. 5). When .sup.224Ra decays, the short-lived .sup.220Rn emanates from the quartz wool and causes absorption of the longer-living decay product, .sup.212Pb, onto the interior surfaces of the flask. The flask can be removed from the cap without the glass coming in contact with the quartz wool. After removing the flask from the generator cap, the flask can be rinsed on the inside with 0.1 M HCl to dissolve the .sup.212Pb deposits whereby a highly purified .sup.212Pb solution is made. The operation and washout of the generator flask is made prior to radiolabeling of NG001. The purity of .sup.212Pb vs .sup.224Ra in the solution is, when the generator is operated in a correct manner (i.e. that the source does not come into contact with the walls), better than 99.8%. The generator can be re-used by attaching a new glass bottle to the generator cap and store for typically 1-2 days for the generation of fresh .sup.212Pb.

[0126] In summary, the generator method is easier to use and less time consuming compared with ion exchange-based generators. The generator may be re-used several times (although with a decreasing capacity due to radioactive decay depending of source half-life).

Example 14: Size of Collector Flask

[0127] The flask sizes of 10, 50 and 100 ml was tested (FIG. 5, upper part). .sup.224Ra was added to quarts wool placed in the cap of flasks placed upside down. The % .sup.212Pb on the flask compared with the theoretical yield varied from about 40% to 60%. It tended to be an advantage to use a larger flask to cap inner surface volume to obtain high yield. In conclusion, flasks with various sizes could be used for generator purposes but a relatively large flask vs. cap seemed to improve .sup.212Pb yield as relatively less would be lost due to absorption on the cap and the source material.

Example 15: Materials for Holding the Source

[0128] To hold the source material in place inside the generator, e.g., in the inner cap center, Steel wool, glass wool, quartz wool was tested with .sup.224Ra sources. The materials are porous and fluffy and allows for diffusion. A volume of 100-150 microliter of .sup.224Ra in 0.1 M HCl was deposited onto the materials placed inside the caps of 100 ml flasks. After standing for 2-3 days or more, 52-64% of the .sup.212Pb compared to .sup.224Ra present in the generator would have settled on the glass surfaces, so all the three materials would work. i.e., quartz wool averaged of 5 tests, 59.9% (range 52.1-64.4%), glass wool 54.9% and steel wool 64.1% for one test each as compared to .sup.224Ra activity in the generator. In conclusion, several different materials could be used to hold the source in the one chamber diffusion generator.

Example 16: Sources

[0129] The radionuclides .sup.224Ra and .sup.228Th were used as sources inside the generators. The .sup.224Ra-based generator could be used typically repeatedly up to a few weeks while the .sup.228Th-based unit could be used repeatedly for several months and deliver .sup.212Pb by simply switching the glass flask with an unused one and wash the first flask to produce a .sup.212Pb solution. Yield was not significantly reduced with repeated use except for the decay of the generator radionuclide. As long as the sources are centered inside the cap to avoid contact with the glass bottle, and flasks and caps are kept dry, cross contamination from source to the glass flask was minimal. In conclusion, the single chamber diffusion unit could be used repeatedly for producing .sup.212Pb with both .sup.228Th and .sup.224Ra as the sources. Lead-212 activity on the inner glass surfaces from .sup.228Th a source was found to be on average 49.3% (range 40.9%-66.7%) from four tests.

Example 17:

[0130] Preparation including heating: To heat up flask before mounting onto the cap with the source material could be a way to produce reduced pressure in the generator. The flask was heated to 90° C. in a heat chamber for at least 15 minutes and then the flask and cap was screwed tightly together to be gas tight. The generator unit was thereafter stored at room temperature causing reduced inner pressure. After 1-4 days the chamber was opened and the .sup.212Pb activity on the glass flask was measured. The yield from four tests using .sup.224Ra on quartz wool was on average 68.1% (range 60.5%-75.9%, indicating improved yield compared with previous data for normal pressure flasks (average 59.9%). In conclusion, reduced chamber pressure may improve the yield of .sup.212Pb with the one chamber diffusion generator.

Example 18: Yield of .SUP.212.Pb in the Washout Solution

[0131] A standard solution of 0.1 M HCl was used for extracting the .sup.212Pb trapped on the inner glass surface of 100 ml flasks. The washing solution was carefully shaken and swirled to cover the inside of the flasks for about 2 minutes and then 80% of the volume was taken out and measured and compared with the total count of the flask before the washing procedure. It was assumed that the 80% volumes should be divided by 0.8 to determine the total activity in the liquid. With 0.6 ml about 85% was extracted and with 1 ml 93% was extracted with similar washing effort. From .sup.224Ra based generator on average 86.1% (range 79.4%-93.4%) for 8 tests was extracted from the glass bottles. From .sup.228Th based generator on average 86.5% (range 84.5%-88.5%) for two tests was extracted from the glass bottles. In conclusion, .sup.212Pb trapped on the inner glass surfaces in the generators are easily extracted with 0.1 M HCl.

Example 19. Radiolabeling Reactivity of Solutions

[0132] The TCMC-chelator-based molecule NG001 (Stenberg et al 2020) was used for testing .sup.212Pb labeling with the generator extracted .sup.212Pb. Lead-212 in 0.1 M HCl was added sodium acetate to adjust pH to about 5.5. Thereafter, NG001 was added to 10-20 micrograms per ml. After 30 minutes reaction on 37° C. using a Thermomixer (Eppendorf, Germany), samples were withdrawn and thin layer chromatography (TLC) was performed by mixing the samples 1:2 with 1 mM EDTMP in 7.5% bovine serum albumin solution and let it stand for 5 minutes. Thereafter 1-5 microliter was applied onto a chromatography strip (model #150-772, Biodex) and eluted with 0.9% NaCl solution in a beaker. When the liquid front reached the top of the strip, it was cut in two halves, each placed in a tube and counted separately in a Packard Cobra II gamma counter (Packard Instruments Co Inc, USA). The data showed that after 3 hours the activity of the bottom half would make up typically >99% indicating almost quantitative yield. Blind test without the NG001 but all the other compounds would give less than 3% on the bottom half of the strip indicating good selectivity for the TLC test. In conclusion, the .sup.212Pb extracted from the generator flask showed excellent reactivity, indicating suitability for radiopharmaceutical use.

Example 20. Radiochemical Purity of Extracted Solutions

[0133] Lead-212 solutions were stored for 10 days or more and recounted for measuring .sup.224Ra. The .sup.224Ra activity was decay corrected back to time 0. The .sup.224Ra vs .sup.212Pb was determined to be on average 0.045% (range 0.01%-0.13%). In conclusion, the .sup.212Pb produced from the generator had high radiochemical purity relevant for pharmaceutical use.