Reactor production and electrochemical purification of (169)Er: a potential step forward for its utilization in in vivo therapeutic applications.
BACKGROUND
The aim of the present study was to develop and demonstrate a viable method for the reactor production of (169)Er with acceptable specific activity using moderate flux reactor and its purification from (169)Yb following electrochemical pathway based on mercury-pool cathode to avail (169)Er in radionuclidically pure form essential for its therapeutic use.


METHODS
Erbium-169 was produced in reactor by neutron bombardment of isotopically enriched (98.2% in (168)Er) erbium target at a thermal neutron flux of ~8×10(13) n.cm(-2).s(-1) for 21 d. A thorough optimization of irradiation parameters including neutron flux, irradiation time and target cooling time was carried out. The influence of different experimental parameters for the quantitative removal (169)Yb from (169)Er was investigated, optimized and based on the results; a two-cycle electrochemical separation procedure was adopted. The suitablility of purified (169)Er for application in radiation synovectomy and bone pain palliation was ascertained by carrying out radiolabeling studies with hydroxypaptite (HA) particles and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminomethylene phosphonic acid (DOTMP), respectively.


RESULTS
Thermal neutron irradiation of 10mg of isotopically enriched (98.2% in (168)Er) erbium target at a flux of ~8×10(13) n.cm(-2).s(-1) for 21 d followed by a two-step electrochemical separation of (169)Yb impurity yielded ~3.7GBq (100mCi) of (169)Er with a specific activity of ~370MBq/mg (10mCi/mg) and radionuclidic purity of >99.99%. The reliability of this approach was amply demonstrated by performing several production batches, where the performance of each batch remained consistent. The utility of the purified (169)Er was demonstrated in the radiolabeling studies with HA particles and DOTMP, wherein both the radiolabeled products were obtained with high radiolabeling yield (>99%).


CONCLUSIONS
A viable strategy for the batch production and purification of (169)Er, suitable for therapeutic applications, has been developed and demonstrated.
Isotope Application and Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
Rubel
R
Chakravarty
Isotope Application and Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
Sudipta
S
Chakraborty
Isotope Application and Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
Viju
V
Chirayil
Isotope Application and Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India. Electronic address: adash@barc.gov.in.
Ashutosh
A
Dash
D004563:Electrochemistry / Q000379:methods*; D004871:Erbium / Q000737:chemistry* / Q000627:therapeutic use*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008628:Mercury / Q000302:isolation & purification; D009502:Neutrons; D009943:Organophosphorus Compounds / Q000737:chemistry; D011854:Radiochemistry / Q000379:methods*; D011868:Radioisotopes / Q000737:chemistry* / Q000627:therapeutic use*; D015018:Ytterbium / Q000302:isolation & purification
D009943:Organophosphorus Compounds; D011868:Radioisotopes; C082084:1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonic acid); D004871:Erbium; D008628:Mercury; D015018:Ytterbium
(169)Er; (169)Yb; Bone pain palliation; Electrochemical separation; Radiation synovectomy; Radionuclidic impurity