TITLE:
Dosimetric Effects of a Commercial Breast Board Patient Support System
AUTHORS:
Eve Schodowski, Austin Wilkinson, Sadik Khuder, David Pearson
KEYWORDS:
Prone Breast Treatment, Breast Board, Attenuating Structure, Interfraction-al Set-Up, Patient Support System, Robustness
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.11 No.1,
December
27,
2021
ABSTRACT: Aim: 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 adding 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 patients’ positions are accounted for. Furthermore, transmission measurements are usually
carried out perpendicular to the board, a non-clinical situation. The goal of this study is to
evaluate the dosimetric effect of the board and the robustness of the plan to positional uncertainty. Materials
and Methods: Twenty-two 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 removed from
the dose calculation. To quantify the robustness of this technique, we moved the beam isocenter
with respect to the patient and board. Results: Our results showed that when the breast board is removed from
a plan which was designed to account
for the board attenuation, the average point dose increases by 7.48%, with a maximum of 22%. Comparing results with a
mixed Analysis of Variance (ANOVA)
and a least-square means analysis, our
robustness evaluation indicates that anterior shifts at every magnitude (1 mm through 5 mm) make a significant
difference in all dose statistics (D95, max, 95% prescription coverage and homogeneity index) investigated. In/out and
right/left shifts resulted in an insignificant change in dose
statistics. Conclusion: Prone breast boards
can add significant dosimetric
uncertainty into the treatment delivery process. Accounting for plan robustness in the design of the
plan is highly recommended. A prone breast board design with support moved away from the beam path is warranted.