Impact of different dose prescription schedules on EQD2 in high-dose-rate intracavitary brachytherapy of carcinoma cervix

Purpose To observe the effect of different high-dose-rate (HDR) intracavitary brachytherapy dose schedules on equieffective dose in 2 Gy per fraction (EQD2). Material and methods It is a retrospective study involving 50 cervical cancer patients, who received external radiotherapy of 45 Gy in 25 fractions and underwent intracavitary brachytherapy (ICBT). Computed tomography (CT) simulation was done after insertion of the applicators. High-risk clinical target volume (CTVHR) and organs at risk (OARs) such as bladder, rectum, and sigmoid were contoured. Four different plans were generated for each patient, with dose prescriptions of 5.5 Gy × 5 fractions (plan A), 6.5 Gy × 4 fractions (plan B), 7 Gy × 4 fractions (plan C), and 9 Gy × 2 fractions (plan D), delivered to CTVHR. The total EQD2 for 0.1 cm3 and 2 cm3 of bladder, rectum, and sigmoid as well as dose received by 90% of the CTVHR (D90) and point A were calculated. The values were analyzed and compared with available literature. Results The mean CTVHR volume was 47.12 ±13.8 cm3. All plans delivered similar EQD2 for 0.1 cm3 and 2 cm3 of sigmoid. Plan D delivered lesser EQD2 compared to other plans for bladder, rectum, D90 CTVHR, and point A (p = 0.0001). Plan C delivered higher EQD2 to OARs compared to other plans (p = 0.001). Plan A, B, and plan C delivered similar EQD2 for D90 CTVHR and point A. Conclusions EQD2 of bladder, rectum, sigmoid, D90 CTVHR, and point A were similar with 5.5 Gy × 5 fractions, 6.5 Gy × 4 fractions, and 7 Gy × 4 fractions, whereas EQD2 of 9 Gy × 2 fractions was significantly unfavorable compared to other schedules. Further clinical studies are recommended to observe clinical outcomes.