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Clinical Implementation of Acuros-XB From AAA for Breast: Changes in Plan Characteristics

L Conroy

L Conroy1*, A Guebert2 , S Weppler2 , M Alghamdi1 , J Conway1 , L Harper2 , T Phan1 , I Olivotto1 , W Smith2 , S Quirk1 , (1) The University of Calgary, Calgary, AB, (2) Tom Baker Cancer Centre, Calgary, Alberta


SU-I-GPD-T-435 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Two dose calculation algorithms are available in Varian Eclipse software: Anisotropic Analytical Algorithm (AAA) and Acuros External Beam (AXB). Many Varian Eclipse-based centers have access to AXB; however, some physicians are reluctant to implement a new dose calculation algorithm without a thorough understanding of how it will affect plan characteristics and, subsequently, clinical practice. We characterized the difference in breast plan quality between Acuros-XB and AAA for dissemination to clinicians during implementation.

Methods: Field-in-field locoregional plans were created in AAA for 30 breast cancer patients in deep inspiration breath hold. The prescription dose was 50Gy for the breast and 45Gy for the supraclavicular in 25 fractions. The target dose for the internal mammary chain (IMCCTV) nodes was 40Gy. Plans were recalculated using AXB with constant MU values. Target coverage and organ at risk doses were compared using dose volume parameters. The breast contour was divided into nine sub-volumes in the superior-inferior and left-right directions for analysis of location-specific changes.

Results: Minimal differences were found between the AXB and AAA plans. The median difference between AXB and AAA for breast CTV V95%, IMCCTV V95%, and V80% were 1.0%, -4.5%, and 0.0%, respectively. IMCCTV coverage decreased when IMCs were marginally covered (V95%). Mean skin dose increased by a median of 3.2Gy when calculated with AXB. In the sub-volume analysis, the medial sub-volumes were ‘hotter’ when recalculated with AXB and the lateral sub-volumes ‘cooler’ with AXB; however, all differences were within 2Gy.

Conclusion: Clinical implementation of AXB from AAA for breast will result in minimal differences in plan quality and plan appearance for locoregional field-in-field plans. Skin dose is likely the only clinically significant difference that will be observed when implementing AXB in this context. Further work is required to evaluate the implications of using AXB for IMRT and partial breast plans.

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