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Setup Beam Geometry Optimization for Tangential Whole Breast Radiation Therapy (WBRT)

W Wang1*, Y Sheng2 , S Yoo2 , R Blitzblau2 , F Yin2 , Q Wu2 , (1) Duke Kunshan University, Suzhou, Jiangsu, (2) Duke University Medical Center, Durham, NC


(Monday, 7/30/2018) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 3

Purpose: To develop an automated workflow to generate optimal beam setting for whole breast radiation therapy (WBRT).

Methods: Twenty breast cancer patients receiving tangential WBRT were included in this study. CT images and breast surface catheters were used to determine patient-specific beam setting. Beam setting includes five parameters: gantry angles, isocenter location, field size, collimator angles, and MLC shape. To optimize the beam parameters, a geometry-based objective function was constructed, which is the weighted sum of the square of the relative out-of-field PTV volume and in-field ipsilateral lung volume. The balance between target coverage and lung sparing was trained and leave-one-out validated among twenty cases. An initial beam was calculated based on the CT images, the catheters, and breast PTV volume. The search for the optimal beam (minimal objective function) was conducted in a 2-dimensional grid of gantry angle and isocenter location with the initial beam as the origin. The setup plan with the optimal beam was transferred to an in-house automatic fluence optimization program developed for tangential fields. The automatic plans were compared with the manually generated clinical plans for PTV and OAR doses.

Results: Calculation time of beam optimization was under one minute. The automatic plans have overall comparable plan quality as clinical plans: breast PTV V₉₅ were all above 95%, and average V₉₅ was higher than that of clinical plans (97.7% vs. 96.8%); average ipsilateral lung V�₆ was lower (12.6% vs. 13.6%); average heart mean dose was slightly higher (2.06% vs. 1.99%).

Conclusion: A beam setting optimization program for tangential WBRT was developed. Plans with automatically generated beam setting were overall comparable with clinical plans. The program offers a valuable tool for WBRT planning, as it provides clinically relevant solutions based on previous clinical practice as well as patient specific anatomy.


Breast, Beam Shaping, Optimization


TH- External beam- photons: treatment planning/virtual clinical studies

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