Room: Exhibit Hall
Purpose: This is the first ever study to compare the DVH parameters of intracavitary and interstitial brachytherapy (ICBT/ISBT) plans using the Venezia and Split-ring & Tandem applicators.
Methods: From July 2017 to February 2018, four patients with FIGO stage IIA and IIB were treated with both the Venezia applicator (Elekta, Stockholm) and the Split-ring & Tandem applicator (Elekta, Stockholm) for brachytherapy boosts (ICBT/ISBT). Three patients received 7Gy for 4 fractions and one patient received 6Gy for 5 fractions. Three patients were treated for two fractions and one patient was treated for one fraction with the Venezia applicator, while the Spit-ring & Tandem applicator was used for the rest of the treatments. Targets (GTV, IR-CTV, HR-CTV) and OARs (rectum, bladder, bowel, sigmoid) were contoured based on multi-parametric MRI and CT. Treatment plans were generated using the Oncentra TPS based on CT. Dose for each fraction was normalized to 2Gy-equivalent (EQD2). D90 for HR-CTV, IR-CTV, GTV, OARs D2cc and vaginal wall doses were evaluated for both the Venezia applicator and the Split-ring & Tandem applicator. The gynecologic dose reporting worksheet from American Brachytherapy Society (ABS) was used to ensure all the plans met the GEC-ESTRO and ABS guidelines.
Results: Mean difference in D90 for HR-CTV, IR-CTV and GTV between plans with Venezia with respect to Split-ring & Tandem applicators were: -5.4%Â±6.5%, -10%Â±20.1%, and 19.9%Â±4.5%, respectively. Difference in D2cc for bladder, rectum, sigmoid, and bowel were: -23.7%Â±15.1%, -27.3%Â±22.5%, 4.4%Â±48.2%, and -6.1%Â±33.1%, respectively. Difference in left and right vaginal wall point doses were 33.1%Â±46.0% and 21.2%Â±40.8%, respectively.
Conclusion: Compared with the Split-ring & Tandem applicator, the Venezia applicator can provide comparable HR-CTV coverage and superior GTV coverage. In addition, doses to critical structures such as bladder and rectum are lower with the Venezia, although dose spillage to the vaginal wall may need more attention.