Dosimetry of 125Ⅰ seeds in different curvatures of bile ducts / 中华放射医学与防护杂志

ABSTRACT

Objective To study the dosimetry distribution of 125Ⅰ seed chains with different radians in different curvatures of bile ducts. Methods The outlines were drawn on the papers, which are the seed chain models with different radians. Radians formula (radian length=2πr × angle/360) was used to calculate the corresponding 0°, 30°, 60°, 90°, 120°, 150° and 180° models with a radian length at 45 mm, for the total length of seed chain model was 45 mm, and the seeds, had no interval or linear arrangements. The image was transmitted to the Brachytherapy planning system for seeds implantation( TPS) to simulate the seed chains with different radians. Using TPS to delineate the tumor target area, of which the activity was set as 1. 85 × 107 Bq, and the prescription dose was 60 Gy. It was prescribed to simulate the bile duct ( diameter at 8 mm) . TPS were used to calculate the D90 and V100 of the simulated bile duct with the diameter at 8 mm, and explore dosimetry of the points at the centripetal and centrifugal sides with 5 mm vertical distance which from two endpoints and center of seed chains with different radians. Results When the radian of seed chain was 30°, the D90and the V100 were the highest (the D90 was 132 Gy; the V100 was 100%). While the radian was 60°, the D90 and the V100 were the lowest (the D90 was 45 Gy, the V100 was 68%). As the radian was 30°, the highest dose was in the center ( dose in the centripetal side was 165 Gy, and centrifugal side dose was 142 Gy) . The center has the lowest dose as the radian up to 180°(dose in the centripetal side was 90 Gy, and centrifugal side dose was 50 Gy) . Among all radians, dose in the centripetal side was always higher than centrifugal side in the center. Between two endpoints, dose in the centrifugal side was higher than centripetal. Conclusions Distribution of seed chain dosage also changed along with the change of radian. When the radian of seed chain was 30°, the D90 and the V100 were the highest. The centripetal dose was higher than that of the centrifugal side.