Impact of different dose prescription schedules on EQD(2) 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 (EQD(2)). 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 CTV(HR). The total EQD(2) for 0.1 cm(3) and 2 cm(3) of bladder, rectum, and sigmoid as well as dose received by 90% of the CTV(HR) (D(90)) and point A were calculated. The values were analyzed and compared with available literature. RESULTS: The mean CTV(HR) volume was 47.12 ±13.8 cm(3). All plans delivered similar EQD(2) for 0.1 cm(3) and 2 cm(3) of sigmoid. Plan D delivered lesser EQD(2) compared to other plans for bladder, rectum, D(90) CTVHR, and point A (p = 0.0001). Plan C delivered higher EQD(2) to OARs compared to other plans (p = 0.001). Plan A, B, and plan C delivered similar EQD(2) for D(90) CTV(HR) and point A. CONCLUSIONS: EQD(2) of bladder, rectum, sigmoid, D(90) CTV(HR), and point A were similar with 5.5 Gy × 5 fractions, 6.5 Gy × 4 fractions, and 7 Gy × 4 fractions, whereas EQD(2) of 9 Gy × 2 fractions was significantly unfavorable compared to other schedules. Further clinical studies are recommended to observe clinical outcomes.