The effect of pelvic radiotherapy on vaginal brachytherapy cylinder diameter: Implications for optimal treatment order

Purpose To determine the factors that correlate with cylinder size in vaginal brachytherapy (VB) after hysterectomy for endometrial carcinoma. Methods and Materials Patients treated for endometrial cancer from January 1, 2003 to December 31, 2013 were reviewed from a single institution. Patients included underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy followed by high-dose-rate VB with or without external beam pelvic radiotherapy (EBRT). According to institutional guidelines, the vaginal cylinder size selected was the largest diameter cylinder the patient could comfortably accommodate. Patient, tumor, and treatment factors were recorded and compared with cylinder size. Results Three hundred eighty-one eligible patients were identified, including 121 patients treated with pelvic radiotherapy (RT) before VB and 260 treated with VB alone. On univariate analysis, weight (p = 0.0004), body mass index (BMI) (p = 0.001), and receipt of pelvic RT (p ≤ 0.0001) were the only statistically significant factors correlated with vaginal cylinder size. On multivariate analysis, receipt of EBRT retained significance after adjusting for weight or BMI. In patients receiving VB alone, median cylinder size was 3 cm; after pelvic RT, it was 2.5 cm. Conclusions Higher weight and BMI correlated with accommodation of larger cylinder size. Accounting for this, the receipt of EBRT before VB was associated with smaller cylinder size. Dosimetric data show that larger cylinder size provides superior dose distribution. Although historically the VB boost follows EBRT, reversal of this order may be preferred.