Assessment of air pockets in high-dose-rate vaginal cuff brachytherapy using cylindrical applicators

Abstract

PurposeTo retrospectively assess the incidence and magnitude of air pockets around vaginal cylinders and its impact on dose distribution in vaginal cuff image-guided high-dose-rate (HDR) brachytherapy.Material and methodsFifty endometrial carcinoma patients treated by postoperative HDR vaginal cuff brachytherapy were included in the study. The average age of patients was 58.3 ± 11.8 years (range: 31-87 years). Brachytherapy was performed using cylindrical applicators, and the dose prescribed to 0.5 cm from the applicator's surface, over a length of 5 cm from the applicator's tip. Computed tomography (CT) simulation was used for each brachytherapy fraction. The incidence, vaginal mucosa displacement, volume, and dosimetric effect of air pockets around the vaginal cylinder were evaluated.ResultsA total of 78 air pockets were found in 29/50 patients (58%) and 45/135 (33%) brachytherapy plans. They were located at the apex: 16/78 (20%) and lateral to the applicator: 62/78 (80%). The volume of air pockets ranged between 0.01 and 2.1 cm3 (mean: 0.15 cm3 ± 0.36 cm3), and the maximum displacement of vaginal mucosa from cylinder surface was between 0.1 and 1.09 cm (mean: 0.34 cm ± 0.2 cm). The dose reduction to the vaginal mucosa generated by the air pockets ranged from 0.5 to 66% (mean: 26.4% ± 13.9%).ConclusionsThe presence of air pockets around vaginal cylinder applicators is frequently noticed in post-operative vaginal cuff brachytherapy. The dose to the vaginal mucosa is reduced, as a result of displacement generated by air pockets. The effect on the clinical outcome of this dose reduction is yet to be determined.

Dosimetric assessment of an air‐filled balloon applicator in HDR vaginal cuff brachytherapy using the Monte Carlo method

“…Even a small gap of 1–2 mms can result in a significant dose reduction to the mucosa. As noticed by our and other institutions,3, 4 it is not uncommon to notice from patient CT scans the presence of air gaps at the apex of or along a solid applicator, as long as the vaginal cavity is not in a perfect cylindrical shape after applicator insertion.…”

Experimental verification of Advanced Collapsed‐cone Engine for use with a multichannel vaginal cylinder applicator

“…However, if the dose variation was greater than 20%, which is possible when combining the peak dose increase and baseline dose variation, it may necessitate adjustment of the plan. Another consideration that may contribute to a larger dose variation is the presence of air pockets surrounding the applicator . When considering TG‐43 calculations alone, it was found that 11 of 174 (6.3%) patients were underdosed by an average of 6.1% of the prescribed dose due to displacement of the vaginal mucosa by air gaps .…”

Vaginal cuff brachytherapy in endometrial cancer – a technically easy treatment?

“…Two other reports have reported 32% and 72% of air gaps of >2 mm, respectively,64,75 but the majority are not clinically significant64 and only represent 0.86% of the vaginal surface. The ratio of patients to air pockets has been as high as 58% (29/50) of the patients or 33% (45/135) of the VCB plans 76. Their volume can reach up to 2.1 cm 3 , and the displacement of the vaginal mucosa from the cylinder surface can be up to 1.09 cm.…”

“…Nowadays, simulation for postoperative EC relies on CT volumetric images, which have proven to detect air pockets around the cylinders74,76,77 or inside the rectum84 or evaluate bladder volume79 and improve dose deposition. Magnetic resonance imaging (MRI) is considered the optimal imaging method to delineate volumes in cervical cancer,99 but its value in EC is less clear and availability is limited, so strategies to integrate clinical images into the radiotherapy workflow have been studied 100.…”