Effects of vaginal cylinder position on dose distribution in patients with endometrial carcinoma in treatment of vaginal cuff brachytherapy

Abstract

PurposeTo investigate the impact of different cylinder positions on dosimetry of critical structures in patients with endometrial carcinoma undergoing three-dimensional image-based vaginal cuff brachytherapy (VCB).Material and methodsWe delivered VCB at a dose of 4 Gy to a depth of 5 mm in the vaginal cuff of 15 patients using three different cylinder positions (neutral [N], parallel [P], and angled [A]) according to the longitudinal axis of the patient. We analyzed the dose-volume distribution and volumetric variability of the rectum and bladder. We converted the total doses to equivalent doses in 2 Gy (EQD2) using a linear-quadratic model (a/b = 3 Gy).ResultsThe mean rectum volume for the N, P, and A positions was 68.2 ± 22.7 cc, 79.3 ± 33.7 cc, and 74.2 ± 29.6 cc, respectively. The mean rectum volume for the P position was significantly larger than that for the N position (p = 0.03). Relative to the N position, the A position resulted in a lower total EQD2 in the highest irradiated 2 cc (D2cc; p = 0.001), 1 cc (D1cc; p = 0.004), and 0.1 cc (D0.1cc; p = 0.047) of the rectum. Similarly, the P position resulted in a lower EQD2 in the D2cc (p = 0.018) and D1cc (p = 0.024) of the rectum relative to the N position. In the bladder, the P position resulted in a higher EQD2 in the D2cc relative to the N position (p = 0.02). There was no dosimetric difference between the P and A positions in either the rectum or the bladder.ConclusionsVaginal cuff brachytherapy in the P and A positions is significantly superior to that in the N position in terms of rectum dosimetry. The bladder dose in the N position is considerably lower than that in the other positions.

Vaginal toxicity after high-dose-rate endovaginal brachytherapy: 20 years of results

“…Different data in literature showed one correlation between total dose prescribed, doses for fractions, length of vagina treated, and vaginal late toxicity [8,48,49,50,51,52,53,54,55,56,60,61,62,63,64,65]. Sorbe et al .…”

Vaginal cuff brachytherapy practice in endometrial cancer patients: a report from the Turkish Oncology Group

“…Patient’s anatomy and filling of the rectum and bladder have significant effects on the dose distribution, based on results from both dosimetric and prospective studies [ 15 , 18 - 22 ]. Hung et al .…”

Vaginal cuff brachytherapy: do we need to treat to more than a two-centimeter active length?

“…The VC can move up to 34.5 mm during EBRT [20]. These are largely due to variations in the bladder and rectum volumes between fractions, but a cylinder can also cause different displacement of adjacent organs based on patient's and stand's positioning [21,22]. With suspender immobilization, the vaginal cylinder neutrally follows and stretches patient's vaginal canal, which minimizes air pockets and improves coverage at 0.5 cm depth, additionally allowing for adjustments that conform to motion of the vaginal canal.…”

“…Vaginal cuff movement can be significant from bladder and rectum volume variation [20,21]. The vaginal cylinder itself can also cause displacement and altered dose distribution depending on how it is positioned [22]. Traditional table-mounted immobilization (i.e., stand) of the vaginal cylinder is susceptible to inter-and intra-fraction changes in patient positioning.…”