Studies on the production and quality assurance of miniature 125I radioactive sources suitable for treatment of ocular and prostate cancers

(125)I sources were prepared by adsorption of (125)I on palladium-coated silver wires. The effect of reducing agent on percentage adsorption of (125)I was studied and the amount of adsorbed activity on source core was studied by repeated adsorption cycles. The activity per source in the sources produced from the same batch varied with coefficient of variation (i.e. the ratio of standard deviation to mean multiplied by 100) less than 10%. The unencapsulated source exhibited low leachability (< 0.01%). The laser parameters were optimized to obtain quality welds with negligible leak rate. The sources were laser-encapsulated in titanium capsules of 0.8 mm (OD) x 4.5mm (l). The release of radioactivity from encapsulated sources in an immersion test at 50 degrees C for 5 h was <5 nCi (185 Bq). The surface contamination on the sealed capsules was found to be<0.05 nCi or 1.85 Bq per source. The sources were used in the treatment of a child having retinoblastoma.

Dosimetry parameters of BARC OcuProsta I-125 seed source

A new model of 125I seed source, named OcuProsta seed, was designed and fabricated by Radiopharmaceuticals Division of Bhabha Atomic Research Centre for ophthalmic and interstitial applications. AAPM TG 43 recommended dosimetry parameters for this seed source were determined experimentally using TLD as well as by Monte Carlo (MC) simulation. Measured and MC calculated values of the dose rate constant (DRC) are 0.95 +/- 0.065 cGyh(-1)U(-1) and 0.972 +/- 0.005 cGyh(-1)U(-1), respectively. The mean of measured and calculated DRC (lambda = 0.96 cGyh(-1)U(-1)) was recommended for the clinical dosimetry of OcuProsta seed. Measured and MC calculated radial dose function, g(r), anisotropy function, F(r,theta), anisotropy factor and anisotropy constants are also found to be in good agreement to each other. Dosimetry parameters of OcuProsta seed were compared with the published values of similar in-design 125I seed sources. The DRC of BARC OcuProsta seed is very close to Amersham 6711 seed and is also comparable to the DRC of Best model 2301, Syncor PharmaSeed and Isotron selectSeed within the uncertainty of measurement/calculation. The g(r) of OcuProsta seed shows a difference of up to 10% in comparison to the g(r) values of the similar in-design seed sources. The values of anisotropy function of OcuProsta are 7-13% different from the anisotropy function of Amersham 6711 and Syncor PharmaSeed. The anisotropy constant of OcuProsta is close to Amersham 6711 seed while it is about 9% smaller than the anisotropy constant of Best model 2301 and Synchor PharmaSeed.

A general formula for computation of tissue-air ratios for radionuclides commonly used in brachytherapy

Tissue-air ratio values for different radionuclides have been computed from first principles. The computed data have been used to derive a general formula applicable to most commonly used radionuclides in brachytherapy. There is good agreement between the values obtained from the present formulation and other reported values. For depths beyond 10 cm, no reported values are available for comparison, but on the basis of the self-consistency of the formalism it is reasonable to expect the accuracy of the computed values to be within +/- 2% at any depth up to 30 cm.

Mould therapy using cathetron source pencils

The use of Cathetron source pencils for planar, linear and cylindrical mould applications has been worked out. Since the source distributions based on Paterson-Parker rules involve the use of the same source pencil for a number at different positions on the mould, an alternate arrangement has been worked out which makes use of more than one type of pencil, thereby minimizing the irradiation time. Dose distributions have been obtained for three sizes of planar moulds and two sizes of linear and cylindrical moulds for different treating distances.