Dosimetric comparison of two different applicators and rectal retraction methods used in inverse optimization-based intracavitary brachytherapy for cervical cancer

PURPOSE: The purpose of this study was to evaluate the dosimetric differences between two different applicators and rectal-retraction methods used in image-guided brachytherapy (IGBT) for locally advanced cervical cancer (LACC). MATERIAL AND METHODS: Ten patients with LACC treated with definitive chemoradiotherapy and inverse optimization-based IGBT were included in this study. In each patient, at least one fraction of IGBT was performed using tandem-ovoids (TO) with vaginal gauze packing (VGP) or tandem-ring (TR) with rectal-retractor (RR). High-risk clinical target volume (CTV(HR)) and intermediate-risk CTV (CTV(IR)) were defined as CTVs, and bladder, rectum, sigmoid, small bowel, urethra, and vaginal mucosa were defined as organs at risk (OARs). All patients received 50.4 Gy external beam radiotherapy (EBRT) in 28 fractions. After EBRT, 28 Gy high-dose-rate (HDR) IGBT in 4 fractions was delivered to central disease. A plan comparison was performed using dose-volume histogram (DVH) and treatment planning parameters for CTVs and OARs. RESULTS: There were no significant differences in D(90) values of CTV(HR). In terms of rectum dose, TR with RR was found to be significantly better than TO with VGP (p < 0.0001 for D(2cm3) and p < 0.013 for V(5Gy)). Although, there were no statistically significant differences in D(2cm3) value of bladder, sigmoid, small bowel, upper vaginal mucosa, and urethra, mean value of D(2cm3) for all defined OARs were found lower in TR than in TO. Bladder V(7Gy), upper vaginal mucosa V(7Gy), middle and lower vaginal mucosa D(2cm3) values were all found to be significantly lower for TR than for TO (p < 0.035). CTV(HR) and CTV(IR) volumes contoured in TR were approximately 11% and 9% smaller than TO, respectively. CONCLUSIONS: The results showed that there were no statistically differences in D(90) value of CTV(HR) and CTV(IR). However, all DVH parameters for OARs in TR with RR were found to be better than in TO with VGP.