THERMOLUMINESCENT DOSIMETRY FOR PD-103 SEEDS (MODEL 200) IN SOLID WATER PHANTOM

Dose measurements using LiF thermoluminescent dosimeters (TLD) have been performed for single Pd-103 seeds (model 200) at the center of a solid water phantom. TLD cubes 1 mm on an edge were used for measurements from 1 mm to 1 cm at 1-mm intervals. The cubes were centered along transverse and longitudinal axes and along radial lines from seed center at 10-degrees increments. TLD chips of dimension 3.1 x 3.1 x 0.89 mm were used at distances of 2, 2.5, 3, and 4 cm at 15-degrees angular intervals. Data are presented as the product of distance squared and dose rate per unit source strength, plotted versus distance and angle. At 1 cm from seed center along the transverse axis this product was found to be 0.88 cGy cm2 mCi-1 h-1. A dose-rate table in polar coordinates has been formulated for use with multiseed dose distribution calculations. Comparison with data of Meigooni et al. [Endocuriether./Hyperthermia Oncol. 6, 107-117 (1990)] shows general agreement for distances of 2 cm or greater. A comparison of our transverse axis data with Russell's calculated values (Theragenics Internal Report, 4 November 1984) for an ideal point source of Pd-103 shows very good agreement except at distances less than 0.5 cm, where differences are attributable to the extended source effect in the actual seed.