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Feasibility of Soft Robot Assisted 4pi Supine Breast Radiotherapy

D Shang*, W Gu, Q Lyu, R Neph, K Sheng, UCLA School of Medicine, Los Angeles, CA


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

Room: AAPM ePoster Library

BreastBot shows the potential to create the “prone geometry” in the supine patient position by supporting and immobilizing the breast via inflated air chambers. In this study, we aim to determine the dosimetric benefit of treating the patient in the setup position vs. standard prone position.

Twenty partial breast patients initially simulated in the prone position were included in the study. The prone geometry with supine patient position created by BreastBot was simulated by rotating the prone setup breast patient CT. The collision-free beam angles for the simulated BreastBot supine position and the prone position, respectively, were determined based on the patient and machine CAD model. Two 4p treatment plans, each with 20 non-coplanar beams selected from the collision-free beams, were created for the two setup positions, respectively. The non-coplanar beam selection and fluence map optimization problem was formulated as a group sparsity problem that can be solved using a Fast Iterative Shrinkage Thresholding Algorithm (FISTA). Wilcoxon signed-rank tests were conducted on the maximum and mean doses of all OARs and PTV between the two setup positions. The study includes the following OARs: left lung, heart, and normal ipsilateral breast tissue excluding the PTV.

The number of collision-free beams for supine and prone positions are 351 and 196, respectively. The supine position with simulated prone geometry resulted in distinctly different beams being selected compared with the prone position. The PTV conformity, R50, integral dose, D95, D98, D99 and OAR Dmax and Dmean were significantly reduced in the supine position compared with the prone position due to the superior availability of collision-free beams.

Significantly improved OAR sparing and partial breast target dosimetry were observed in the prone geometry in the supine position using the BreastBot compared with the standard prone position.

Funding Support, Disclosures, and Conflict of Interest: NIH R44CA183390 R43CA183390 VisionRT


Not Applicable / None Entered.


TH- External Beam- Photons: treatment planning/virtual clinical studies

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