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Using Robust Optimization in Raystation to Achieve Flash in Breast VMAT Plans

C Kalavagunta

C Kalavagunta*, G Lasio , University of Maryland, School of Medicine, Baltimore, MD


SU-I-GPD-T-340 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: In this study we evaluate the Robust Optimization (RO) functionality in Raystation (RS) treatment planning system to achieve Breast VMAT (Volumetric Modulated Arc Therapy) plan setup uncertainty robustness.

Methods: Five advanced stage breast patients were randomly selected for this study. The prescription dose ranged from 45–50.4 Gy in 25–28 fractions (1.8–2 Gy/fraction). Dosimetric planning goals were determined from normal tissue tolerances and from the clinical experience of radiation oncologists at our clinic. While a flash region is typically employed to account for respiration induced motion or for anatomical changes during IMRT radiation therapy of the breast, in VMAT planning flash is not straightforward to achieve. To assess the efficacy of RO we created VMAT and Robust-VMAT treatment plans for each patient. A setup uncertainty of 1.5 cm for PTV and OARs was used as robustness setting in the anterior and left/right direction depending on the tumor site. To assess the robustness of the plan the isocenter was shifted by 5 mm in the posterior and left/right direction and the resulting perturbed dose was compared to the nominal plan, optimized without RO. VMAT and Robust-VMAT plans were compared on the basis of dosimetric end points, target coverage (D95%) and OAR doses.

Results: While the presence of skin flash was seen on all robust plans, only 63% of the patients in the study required a robust plan for final delivery. RO plans showed good robustness to 5mm shift with as little as 0.2% change in D98.

Conclusion: A robust optimization method that introduces “skin flash” for breast VMAT plans and maximizes the probability of satisfying the planning criteria in the presence of respiratory motion and setup uncertainty has been evaluated. In all cases the perturbed robust plans led to clinically acceptable target coverage and the presence of skin flash.

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