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Evaluation of the Dose Distributions for HDR Brachytherapy Using Skin Applicator as a Function of Geometry

O Elhanafy1*, A Mahmoudieh2 , B Paliwal3 , B Thomadsen4 , (1) El Portal Radiation Oncology Center, Merced, CA, (2) Elportal Cancer Center, Merced, CA, (3) University of Wisconsin, Madison, WI, (4) University of Wisconsin, Madison, WI


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: The aim of this study was to evaluate the dose distributions for skin cancer treated with HDR Brachytherapy using Freiburg flap applicator with various geometries.

Methods: The cylindrical, water-equivalent phantom was used to simulate a patient with the Freiburg flap applicator. Three different geometries were used. In the first, the applicator was placed directly on the surface of the phantom. For the other geometries, bolus with a thickness of 0.5cm or 1cm was placed between the applicator and the surface of the phantom. The planning target volume (PTV) was delineated with a depth of 0.5cm from the phantom surface. The treatment plans for each geometry used Oncentra TPS optimized to the 100% isodose line. The dose-volume parameters and the total treatment times per fraction are evaluated for each plan.

Results: The treatment plan for the first geometry had PTV 100% receive 97% of the prescribed dose. While the 26% and 6% of the PTV volume obtained 120% and 130% of the prescribed dose, respectively, and the PTVmaximum was 150%. The geometries that used bolus between the applicator and the surface of the phantom show 0.5 cm bolusPTV 100% =98% and 1.0 cm bolusPTV 100% =99% of the prescribed dose, and 0.5 cm bolusPTV maximun =140% and 1.0 cm bolusPTV maximum =130% of the prescribed dose. The total treatment time per fraction for the three different geometries was 16, 20 and 22 minutes respectively.

Conclusion: From these results it is concluded that the position of the skin applicator can markedly affect the brachytherapy dose distributions. Using the 0.5cm and 1.0cm bolus between the skin applicator and the surface are better for skin sparing from hot spot than putting the applicator on the skin. In addition, there is no great significant difference between the overall treatment time for the three geometries.




TH- Brachytherapy: Dose optimization and planning

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