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Evaluation of Patient Positioning Reproducibility with Three Supine Breast Boards

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Y Zhang

Y Zhang*, D Brinkmann , D Pafundi , S Park , E Yan , R Choo , I Petersen , S Childs , T Pisansky , N Remmes , R Mutter , Mayo Clinic, Rochester, MN


SU-C-19A-4 Sunday 1:00PM - 1:55PM Room: 19A

Purpose:To evaluate positioning reproducibility using three commercially available breast board immobilization systems for whole breast radiation therapy.

Methods:Weekly pre-treatment cone beam CT images from 18 free-breathing breast radiotherapy patients, each immobilized with one of three breast boards, were retrospectively registered to the planning CT. Relative shifts between breast tissue and sternum/chest wall (CW), and breast tissue and spine compared to planning CT were obtained for each board. Positioning reproducibility, inter-patient variation and intra-patient variation were evaluated by group mean (M), standard deviation of group mean (Σ) and standard deviation of random shift (σ). Margins to account for setup uncertainties were calculated based on shift uncertainties in x, y, and z directions.

Results:For breast positioning relative to sternum/CW, the average shift from planned positioning was 4.5mm (95% CI: 3.5 – 5.3), 3.3mm (CI: 2.9 - 3.8) and 2.6mm (CI: 1.8 - 3.5) for Breast Boards I, II, and III, respectively. The respective numbers for breast positioning relative to spine were 7.2 mm (CI: 4.1 – 10.3), 6.4 mm (CI: 4.3 – 8.3) and 4.3 mm (CI: 2.5 – 6.2). Localizing to the sternum/CW as a surrogate for the breast tissue, margins for setup uncertainties were 5.7mm, 5.5mm, and 6.0mm for Breast Board I, 5.0mm, 4.0mm and 4.3mm for Breast Board II, and 3.8mm, 3.5mm and 4.8mm for Breast Board III, in the lateral, anterior/posterior, and superior/inferior directions, respectively.

Conclusion: Better patient positioning reproducibility was observed with Boards II and III compared to Board I. Inter- and intra-patient set-up uncertainties were also improved with Boards II and III, which requires smaller PTV margins. Independent of breast board, breast cancer patient positioning to the sternum/CW is a better surrogate than the spine. Our findings have potential dosimetric consequences from set-up uncertainties when employing IMRT or proton treatments, and further analyses are on-going.

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