Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_5_3162 - Will Electronic Brachytherapy be a good candidate for Vaginal Cuff Brachytherapy?

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Will Electronic Brachytherapy be a good candidate for Vaginal Cuff Brachytherapy?
V. W. Kathriarachchi1, J. E. Berilgen2, and S. K. Mani3; 1Advanced Medical Physics, Inc., Houston, TX, 2Millennium Radiation, The Woodlands, TX, 3Advanced Medical Physics Inc, Houston, TX

Purpose/Objective(s): To compare dosimetry, patient set up and technical parameters between vaginal cuff brachytherapy with Electronic Brachytherapy (eBx) and HDR Ir-192.

Materials/Methods: Six endometrial cancer patients treated with Electronic Brachytherapy (eBx) between September 2017 and February 2018 were selected for the analysis. Treatment plans of each patient were re-planned with HDR Ir-192 parameters with 500cGy prescribed to 5mm from the cylinder surface. Evaluation indices of each plan include bladder D2cc and V50%, rectal D2cc and V50%, cylinder apex dose, mid length surface dose and gradient index. Statistical significance was tested using the Wilcoxon signed rank test. Patient set up and technical parameters were evaluated based on set up procedure, treatment delivery and treatment room shielding.

Results: Electronic brachytherapy reduces dose to both rectum and bladder in the lower dose regions. The D50% is significantly lower (Rectal: 3.7cc vs 6.2cc, p=0.06 Bladder: 9.0cc vs 14.0, p=0.06). Electronic Brachytherapy did not spare in the high dose regions, D2cc is similar for both rectum and bladder (Rectal: 63.6% vs 66.9%, p=0.43 Bladder: 9.0% vs 14.4%, p=0.62). Cylinder mid length surface dose was 17% higher (172% vs 147%, p=0.06) for eBx while apex dose was similar to HDR Ir-192 (199% vs 207%, p=0.44). Electronic brachytherapy plans offer improvement of the dose fall off gradient by 34% over HDR Ir-192 (2.07 vs 2.77, p=0.06). The other advantage of eBx is no patient transfer from CT room to HDR vault for treatment delivery. This could potentially lead to more accurate treatment delivery over HDR Ir-192. Additionally, less shielding requirements lead to less expense.

Conclusion: Electronic brachytherapy is a suitable treatment modality for vaginal cuff brachytherapy treatment with several added advantages. These include: a) reduced rectal and bladder doses, b) better dose fall off, c) potentially more accurate treatment delivery and d) reduced room shielding costs when compared to HDR Ir-192. Electronic brachytherapy can produce dosimetrically similar plans with improved cost effectiveness making it an excellent candidate for non-hospital base small clinics using vaginal cuff brachytherapy.

Author Disclosure: V.W. Kathriarachchi: None. J.E. Berilgen: None. S.K. Mani: None.

Vindu Kathriarachchi, PhD

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