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 D₉₀ 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 D₉₀ 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.