Statiscal differences and systematic effect on measurement procedure in thermoluminescent dosimetry of the iodine-125 brachytherapy seed

Abstract

In order to provide the dosimetry for Iodine-125 seed production in Brazil, Harshaw thermoluminescent dosimeters (TLD-100) will be used. Even if measurements with TLD-100 of the same batch of fabrication are performed, the response will not be the same. As a consequence, they must be measured one by one. These dosimeters are LiF type with a micro-cube (1mm x 1mm x 1mm) shape. Irradiations were performed using Iodine-125 seeds to guarantee the same absorbed dose of 5 Gy in each dosimeter. It has been used a Solid Water Phantom with three concentrically circle with 20mm, 50mm and 70mm diameters. The angle of positions used was 0º, 30º, 60º and 90º. Of course there are 2 positions in 0º and 90º and 4 positions in 30º and 60º. These complete procedures were carried out five times in order to compare the data and minimize the systematic error. The iodine-125 seed used in the experiment was take off in each measure and put again turning his position 180º to guarantee the systematic error was minimized. This paper presents also a little discussion about the statistical difference in the measurement and the calculation procedure to determine the systematic error in these measurements.