Dosimetric evaluation of vaginal cuff brachytherapy planning in cervical and endometrial cancer patients

The aim of the study was to perform a prospective analysis of dosimetric consequences of rectal enema administration before vaginal cuff brachytherapy (VCB), the dose distribution in organs at risk (OARs), and the presence of air gaps (AGs) in patients with cervical or endometrial cancer.

In total, 75 patients treated in 2019 were randomly divided into two groups including 38 patients with and 37 without an enema before VCB. All patients received post-operative high-dose-rate (HDR). Single-channel vaginal cylinders with active length of 2.75 cm were used. Prescription dose was 7 Gy at 5 mm depth from the applicator surface in all directions. Treatment plans were based on computed tomography (CT).

Enema performed before cylinder insertion had no effect on rectosigmoid D_max or D_2cm3. Rectosigmoid median V₁₀₀ was 0.5 cm³ (range, 0-2.7 cm³). V₁₀₀ ≥ 1 cm³ in 22 and ≥ 2 cm³ in 6 patients, with D_max up to 19.7 Gy (282%) were observed. No effect of bladder volume in the range of 27-256 cm³ on D_max or D_2cm3 was found. The median bladder V₁₀₀ was 0.1 cm³ (range, 0-1.4 cm³). There were 62 (83%) patients with AGs, with 24% at the top of the vagina and 75% on the remaining length of the vagina. Most of the AGs were small (≤ 3 mm), but in 5 (8%) cases, they were bigger than 5 mm.

VCB planning with the use of CT is essential. CT can facilitate the selection of optimal cylinder size to reduce the occurrence of large AGs. A few percent of plans require correction of dose distribution because of hot spots in OARs and the presence of AGs. Enema before cylinder insertion does not influence rectosigmoid D_max and D_2cm3. The analysis revealed no bladder volume effect on bladder doses D_max and D_2cm3.