Is there any advantage to three-dimensional planning for vaginal cuff brachytherapy?

To evaluate whether the three-dimensional (3D) CT-based high-dose rate planning for vaginal cuff brachytherapy offers any advantage over the 2D orthogonal film-based library plans for adjuvant treatment of endometrial cancers.

Eighty-four consecutive postoperative patients with endometrial cancers treated with vaginal brachytherapy as an adjuvant treatment were analyzed. Patients had CT imaging-based plans. Clinical target volume (CTV) was defined by expanding the upper 2.5cm of the cylinder by 5mm in all directions and editing to exclude any bladder and rectum. The dose prescribed was 7Gy with three fractions at 5mm depth with a goal of D(90) ≥100% for CTV. All dosimetric parameters were compared with library-based plans.

Both the 2D- and 3D-based plans allowed sufficient dosage to the CTV (D(90) for CTV ≥95%). The doses of 0.1, 1, and 2cc to rectum and bladder were significantly higher for 2D-based plans (p≤0.001 in each parameter). D(2 cc) with 2D plan for rectum and bladder was >100% (range: 103-116%) in 7 (8%) and 6 (7%) patients, respectively. In contrast, no patients had D(2 cc) >100% with 3D planning for both organs.

Three-dimensional CT-based planning for high-dose rate vaginal cuff brachytherapy helps to decrease dose to critical organs without compromising coverage of CTV by customizing the dosimetry according to individual patient anatomy.