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# Presentations

(Sunday, 7/14/2019)

Room: ePoster Forums

Purpose: Independent verification of dose calculation remains an indispensable step in high-dose-rate (HDR) brachytherapy treatment workflow to guard patient safety. Many facilities still favor the use of in-house spreadsheet or software to perform this task due to its convenience and zero cost. However, the practice of in-house verification varies, and sometimes the calculated point doses deviate significantly from the plan values, especially for treatments where anisotropy function needs to be accounted for. This work proposes a semi-2D TG-43 formula that can be readily and universally implemented with high accuracy.

Methods: In this formula, we used the point-source approximation for the geometry function, and the fourth-order polynomial fit for the radial dose function as most of the in-house verification methods do. However, our proposed formula further explicitly accounted for the anisotropy of the dose distribution around the source by using a 1D analytical function. This is obtained by first averaging all the 2D anisotropy function data along the dimension of the radial distance and then fitting the averaged data above into a sixth-order polynomial. This 1D anisotropy component is a function of the polar angle instead of the radial distance as in the original 1D TG-43 formula. For evaluation, we implemented our proposed formula for the verification of six HDR intra-operative plans of rectal cancers and compared its performance against the formula without the 1D anisotropy component.

Results: With the proposed formula, the average percentage of dose verification points fell within 2%, 3%, 4% of the planned values for all the six patients is 98%, 100%, 100%, respectively. Without the anisotropy component, the number is 17%, 47%, 57%, respectively.

Conclusion: Our semi-2D analytical TG-43 formula provides accurate verification of the HDR dose calculation even for treatment plans where anisotropy plays a significant role. It can be easily implemented with minimum cost.

Keywords

Taxonomy

TH- Brachytherapy: Calibration & Quality Assurance

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