Journal of Medical Physics and Applied Sciences

Dosimetric Effects of CO-60 and IR-192 Source Step Size in Intra Luminal Brachytherapy

Purpose: The present work reports the effect of source step size on dose distribution in patients treated with cobalt-60 (Co-60) high-dose-rate after loading brachytherapy in esophagus cancer.

Material and methods: A Bebig Multisource^® HDR Brachytherapy unit with cobalt-60 HDR miniature source (Eckert and Ziegler, Bebig, Germany) was used for study. The Co-60 source has an active core 0.5 mm diameter and 3.5 mm active core length. HDR 2.5 plus (Eckert and Ziegler, Bebig, Germany) Treatment planning system was used for the study. 10 patients of carcinoma esophagus were studied for the study of dose distribution around the single intraluminal catheter of 8 cm length. The effect of step size around the catheter was studied for depth doses were calculated at 0, 2.5, 5 mm and 10 mm from the applicator surface. Dose point based optimization and normalization were used to calculate the 4.0 Gy prescription dose at 5 mm depth. Dose distribution and homogeneity for the various source step sizes were evaluated by performing dose computations per step size and calculating the average dose and standard deviation (SD) at each depth.

Results and discussion: The study shows that as the depth increases from 0 to 10 mm, the SD difference decreases with step size for Co-60 and Ir-192 and at the 10 mm depth SD is constant with step size for both sources. The average standard deviation was 0.92, 0.43, 0.27 and 0.14 for depth 0 mm, 2.5 mm, 5 mm and 10 mm respectively. The variation in depth for different step size is decreasing and 2.5 mm step size is more appropriate than 1, 5 and 10 mm step size for both sources. Study in carcinoma esophagus concludes that homogeneity increases as the step size reduces.

Author(s): Pawan Kumar Jangid

Abstract | Full-Text | PDF

Share this