Room: AAPM ePoster Library
This study is to compare OAR doses between vaginal ovoid and cylinder brachytherapy while prescribing the same dose to the targets at the vaginal cuff.
In #1 Ovoid, the gaps between ovoid and vaginal cuff was intentionally created and there was no gap in #2 Ovoid. A 2 cm cylinder was used in #3 cylinder scan. Three different-size targets (5 mm, 7.5 mm and 1 cm in diameter) were created at the vaginal cuff (Fig.1). The patient had EBRT with prescription dose up to 45 Gy. Volume optimization was adopted to cover D90 of CTV with 20 Gy in 4 fractions while setting dose constraints of bladder and rectum to 24.4 Gy and 19.2 Gy using a/ß=3.
In #1 ovoid, D2cc of vaginal wall was increased by 24.55% and 72.64% with increasing CTV sizes respectively (Tab. 1); D2cc of rectum was increased by 54.1% and 83.35% and D2cc of Bladder was increased by 0.54% and 63.52% respectively. In #2 Ovoid, D2cc of vaginal wall was increased by 4.29% and 35.01% with increasing CTV sizes respectively; D2cc of rectum was increased by 15.68% and 39.37% and D2cc of bladder was increased by 2.34% and 29.71% respectively. In #3 Cylinder, D2cc of vaginal wall was increased by 17.63% and 59.43% with increasing CTV sizes respectively; D2cc of rectum was increased by 16.73% and 57.99% and D2cc of bladder was increased by 16.04% and 51.34% respectively.
1. All three brachytherapy plans show increasing OAR doses with increasing tumor sizes;
2. OAR doses are reduced proportionally in the ovoid applicator with no gap compared to the cylinder. However, OAR doses are increased in the ovoid applicator with gap;
3. Therefore, adequate ovoid size is important to make sure that direct contact with vaginal cuff for ovoid brachytherapy.