Objective：To explore the relationship between the tumor size of the high-risk clinical target volume（HR-CTV） and the reverse or conventional plan in CT-based cervical brachytherapy. Methods：Sixty-six patients treated by the CT-based intracavitary brachytherapy for cervical cancer in our hospital from April 2015 to August 2016 were enrolled and divided into 6 groups according to the tumor size[~30 cm3 group（n=9），~45 cm3 group（n=10），~60 cm3 group（n=17），~75 cm3 group（n=11），~90 cm3 group（n=8），and >90 cm3 group（n=11）]. Each patient underwent both the reverse plan and the general plan，the superiority of which was acquired by dose volume histogram（DVH），with D1 cm3，D2 cm3，and Dmean of bladder，rectum and sigmoid colon，6 Gy prescription dose coverage volume，heterogeneity index（HI） and conformal index（CI） as evaluation parameters. Results：①All evaluation parameters in ~75 cm3 group showed no significant difference between the two plan. ②In the groups with tumor size <60 cm3，the reverse plan was superior to the general plan for protecting organs at risks. ③In the groups with tumor size >75 cm3，the general plan was superior to the reverse plan for protecting organs at risks，but inferior for target coverage volume. Conclusion：The research suggests that if the tumor size is smaller than 60 cm3，the reverse plan is superior to the general plan for protecting organs at risks. However，if the tumor size is bigger than 75 cm3，both plans have no significant superiority for protecting organs at risks or target coverage，which suggests that the treat－ment should rely on the implant technique or a combination of the intracavitary brachytherapy and implant technique.
