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Intensity Modulated HDR GYN Brachytherapy

J Dupere1*, JJ Munro III2, DC Medich1, (1) Worcester Polytechnic Institute, Worcester, MA (2) Montrose Technology, Inc., North Andover, MA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
The purpose of this study is to compare the dose distributions of a shielded ring applicator with middle energy HDR brachytherapy sources such as Yb-169 and Se-75 compared to unshielded Ir-192 for gynecological cervix brachytherapy. By using thin amounts of gold, it is possible to modulate the dose distribution to deliver the prescription dose to the cervix while reducing dose to the bladder, sigmoid, and rectum.

Methods:
A Monte Carlo simulation was performed to obtain the dose distribution of a standard ring applicator with Ir-192 in a GYN cervix geometry and for a partially shielded ring applicator with Se-75 and Yb-169. Various thicknesses of shielding and various conical openings of the applicator were calculated for each of these lower energy sources.

Results:
Significant dose reduction to the bladder, sigmoid, and rectum was achieved using small thicknesses of shielding for the Yb-169 and Se-75 sources compared to the Ir-192 source applicator. Se-75 has a TVL of about 3 mm and Yb-169 has a TVL of about 1 mm. When using 3 mm of gold shielding for Se-75, there was a dose reduction of 45% to the bladder, 60% to the sigmoid, and 89.6% to the rectum. When using 1 mm of gold shielding for Yb-169, there was a dose reduction of 27.4% to the bladder, 48.5% to the sigmoid, and 78.4% to the rectum.

Conclusion:
The results show it is possible to modulate the dose distribution of Yb-169 and Se-75 using small amounts of gold, to deliver the prescription dose to the target and protect the surrounding critical structures. The use of this partially shielded applicator would allow for better treatment planning as oncologists would be able to increase dose to the cervix without overexposing the bladder, sigmoid, and rectum.

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