Dosimetric Comparison of Oncentra (Ir-192) and SagiPlan (Co-60) HDR Brachytherapy Planning Systems in Gynaecologic Tumors Using Different Applicator Sizes

Objective: This study aims to compare the dosimetric outcomes of high-dose-rate (HDR) brachytherapy plans using Co-60 and Ir-192 sources implemented through SagiPlan and Oncentra treatment planning systems (TPS), respectively, across different applicator volumes. Methods: CT-based HDR brachytherapy plans were developed using both SagiPlan (Co-60) and Oncentra (Ir-192) TPS for 30 cervical cancer patients. Applicator sizes of 35 cm³, 30 cm³, and 25 cm³ were evaluated. Dosimetric parameters including D90% (dose covering 90% of HR-CTV), conformity index (CI), and organ-at-risk (OAR) doses were analyzed. Total Reference Air Kerma (TRAK) was also assessed. Results: Oncentra (Ir-192) showed improved D90% values with decreasing applicator size: 93.05% (35 cm³), 97.03% (30 cm³), and 96.35% (25 cm³). Conversely, SagiPlan (Co-60) D90% declined from 96.15% to 89.71%. CI was higher with Oncentra (0.72 vs. 0.68 average). OAR sparing was consistently better with Oncentra, with rectal D2cc reduced by up to 5%. TRAK values were similar between systems. Conclusion: Ir-192 plans generated by Oncentra provide improved target coverage and OAR sparing in smaller applicators compared to Co-60 plans using SagiPlan. These findings emphasize the importance of source selection and TPS capabilities in optimizing brachytherapy outcomes