The effect of source step size in uterine cervix intracavitary with high dose rate (HDR) Brachytherapy: A dosimetric comparative study.-

The presented study discusses the impact of source step size on dose distribution in patients undergoing high-dose-rate after-loading Brachytherapy with cobalt-60 (Co-60) for cervical cancer (Ca-cx). Flexitron® Cobalt-60 HDR Brachytherapy unit with Co-60 source, which has an active core 0.5 mm diameter and 3.5 mm active core length was used. Oncertra® Brachy v4.6, (Elekta, Stockholm, Sweden) treatment planning system was also used in patient dose distribution and calculation. The respective study is based on the database of 11 patients Ca-cx already treated with Co-60 intracavitary Brachytherapy with 21 Gy treatment doses for each patient delivered in three fractions after a 45 Gy of external beam radiotherapy. The assessment of the entire treatment process included an examination of the prescribed dose volume, organ-at-risk doses, and treatment time. This analysis was performed for varying source step sizes 1 mm, 3 mm, 5 mm, and 7 mm considering each patient individually. our general results we can conclude that 5 mm step size is the best choice to do brachytherapy plan to achieve organ at risk constrains, treatment time and prescribed dose coverage volume were affected by the increase of source step size.