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Quantifying the Dosimetric Effects of The Breast Immobilization Board by Adding Robustness for Prone Breast Irridiation

K Joseph*, D Pearson, K Joseph, University of Toledo, Toledo, OH

Presentations

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

Room: AAPM ePoster Library

Purpose: female patients with large pendulous breast undergo prone whole breast irradiation in order to reduce acute as well as late toxicities. Studies have shown this technique to be advantageous in reducing the inclusion of the heart, lung as well as reducing the contralateral breast from being within the field. It has been shown that the stability of the dose due to variations in patient setup has impacted overall PTV coverage due to the effects of the prone breast board used for breast immobilization. Therefore to mitigate these effects adding robustness should decrease the dosimetric variability of loss of PTV coverage ; thereby quantifying this effect with the breast board and without the breast board.


Methods: Prone whole breast patients treated with tangential fields between 2018-2020 were retrospectively enrolled into this study. The prescriptions for each of these patients was 266cGY x 16 FXs. Each patients plan was re-planned using RayStation ( Raysearch Laboratories, Stockholm, Sweden) Version 8.01 robustness feature in which position uncertainties were applied universally for all beams between 1mm-5mm in each respective direction; [Superior, Inferior, Right, Left, Posterior, Anterior]. The prescription Isodose line, D99, D98, Average, D50, D2, D1 and Max PT doses were used to asses PTV coverage for each plan with robustness with breast board. Plan comparisons were made for robustness with board, original Plan with and without board.


Results: PTV coverage was achieved for all robust plan yet coverage (D95) showed -19.274% difference from original plan with board and without board. Max point deviation for robust plans were shown to be max of -24.8% of the max dose with board for the original plan and plans with robustness.


Conclusion: The dosimetric impact of the prone breast board effects overall PTV coverage when using robustness to optimize coverage.

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