Analysis of clinical utilization of ring applicator for combined intracavitary/interstitial image-guided brachytherapy treatment in Chinese patients with locally advanced cervical cancer

Introduction
To analyze the results of clinical utilization of ring applicator for combined intracavitary (IC)/interstitial (IS) image-guided brachytherapy (BT) technique in locally advanced cervical cancer (LACC), and to explore the application conditions of IC/IS BT approach with this applicator for Chinese patients.

Material and methods
IC/IS BT was performed in total of 95 LACC patients, who already received external beam radiotherapy. In forty-three of these patients, utilization of ring applicator in brachytherapy was done, including IC/IS BT approach with ring applicator for 65 fractions. Clinically optimized IC/IS BT plan with ring applicator (IC/IS treatment) and additionally generated optimized plan without needle use (IC research) were designed, respectively. Dosage differences in target regions and organs at risk (OARs) were analyzed between both the plans. Four planes were selected in the longitudinal direction of uterine cervix and divided the 360° area around the tandem into eight equal sectors. Tumor target features and prescription dose distributions on different planes were described.

Results
The usage rate of ring applicator with most suitable ring diameter of 26 mm was 45.3% in Chinese cervical cancer patients. The high-risk clinical target volume (HR-CTV) D90/D98 and intermediate-risk CTV (IR-CTV) D90/D98 in IC/IS treatment were significantly higher than IC research. As compared with IC research plan, the D2.0 cm³ of bladder and rectum in IC/IS treatment were significantly lower (p < 0.05). There was no significant difference in D2.0 cm³ of sigmoid and small bowel between two plans. When the target volume was larger than 36 cm³, IC alone had an inadequate coverage of target.

Conclusions
Nearly half of Chinese patients with LACC could be treated with the ring applicator. The application conditions of IC/IS BT approach with ring applicator for Chinese patients were achieved. Combined IC/IS image-guided BT based on magnetic resonance imaging (MRI) planning is clinically feasible in Chinese patients.