Dosimetric Effects of a Prone Breast Board System
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PO-GePV-T-81 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: In prone breast treatments a carbon fiber support device resides under the contralateral breast. Tangent beams are designed to encompass the treated breast and these often pass through the board at a shallow angle, resulting in significant attenuation. Our planners account for this attenuation by added field-in-field dose to the deep part of the breast, through the board. Concern was raised about how accurate the treatment delivery is when the inherent uncertainties of patient position are accounted for. Further, transmission measurements are usually carried out perpendicular to the board; a non-clinical situation. The goal of this study compare the dosimetric effects of treatments delivered with the breast board and without.
Methods: Twenty breast patients treated on a commercial prone breast board between 2017 and 2020 were selected for this retrospective study. To evaluate the board’s attenuation, we compared the plans with the board replaced with a rigid foam for the dose calculation. To quantify robustness of this techniques the plans then were shifted in 1mm increments up to 5mm in the superior, inferior, right, left, anterior, and posterior directions using the RayStation perturbed dose feature.
Results: With the carbon fiber board replaced by rigid foam to support the breast with an attenuation similar to that of air there was a decrease in the max point dose (Average of ~15%, number of MU’s used in the plan (Average of ~9%), mean heart dose (Average of ~19%) and increased homogeneity index (Average of ~4%) these statistics get increasingly worse once accounting for patient setup error.
Conclusion: The current carbon fiber prone breast board causes increased dose to the patient and can be reasonably and easily replaced by rigid foam with attenuation properties similar to that of air allowing for more robust plans and certainty when delivering treatments.
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