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Radiation stability of 125I-brachytherapy sources

Saxena S., Ram R., Dash A., Joshi P., Venkatesh M.

Nukleonika

2007

Vol. 52, nr 1

13-16

Low energy 125I-brachytherapy sources are used for the treatment of retinoblastoma and many other forms of eye cancer. Such sources were prepared by adsorption of 125I on palladium coated silver rods and were critically evaluated for safety aspects, as per AERB standards. In order to attain low leachability and to facilitate leak free laser encapsulation of sources within titanium capsules of size 0.8 mm (f) ´ 4.75 mm (l), the radioactive source core was coated with polystyrene. With a view to study the radiation stability of such sources over a period of three weeks, both polymer coated radioactive sources and inactive source cores were separately subjected to an integrated gamma dose of ~(17.85 ´ 104) Gy (17.85 MRad), which is the dose expected to be received in three weeks from a source containing ~ 111 MBq of 125I. This was carried out to test their suitability for reuse within such period. SEM pictures of inactive source cores were taken to observe the effect of gamma radiation on palladium coating. Post-irradiation leachability and uniformity of activity of radioactive sources were evaluated and found to be satisfactory. The sources were found to be reusable safely, for repeated brachytherapy procedures over a practically useful time of at least three weeks.

Kinetics and Mechanism of Complex Formation between O-Bonded Pentaammine(valinato/prolinato)cobalt(III) Ions and Nickel(II) in Aqueous Medium

Dash A., Brahma G., Mohanty P., Das R.

Polish Journal of Chemistry

2004

Vol. 78 / nr 7

987-995

The kinetics of reversible complexation of Ni(OH2)6 2+ with oxygen-bonded valinato/prolinatocobalt( III) substrates, (NH3)5Co(val/pro)3+ have been investigated by stopped flow technique at 25_C, 6.1_ pH_6.70 and I = 0.3 mol dm-3. The formation of binuclear species, [(NH3)5Co(val/pro)Ni]4+, occured via the reaction of Ni(OH2)6 2+ with deprotonated (amine and imine functions of valine and proline, respectively) form of the cobalt(III) substrates, (NH3)5Co(val/pro)2+. The results indicate the formation of mono-bonded binuclear species through entry of the imine/amine functions into the coordination sphere of Ni(II) with Ni-OH2 bond dissociation is limiting (Id mechanism). The binuclear species exist in dynamic equilibrium involving the mono-dentate and chelated forms with chelated forms predominating. The small values of dissociation rate constants, despite the intrinsic electrostatic repulsion between the like charge centers, also support the chelate nature of the binuclear species.