Room: Exhibit Hall | Forum 7
Purpose: Heart-sparing during radiotherapy of left-sided breast-cancer patients, requiring comprehensive regional-lymph-node therapy targeting any residual breast tissue, underlying chest-wall, and axillary, supraclavicular, and internal-mammary nodal basins (LBrCw/LNs), is vital and challenging. The objective of this study was to optimize VMAT technique for LBrCw/LNs patients for Halcyon-delivery system using 6MV-flatness-filter-free beam of limited-field-size defined by a double-stack MLCs.
Methods: HalcyonPlans were generated for twelve LBrCw/LNs patients (8-left, 4-bilateral) using up to 10-ipsilateral arcs with unique collimator angles and 1 or 2-isocenters. Two patients planned with 6-arcs at a single-isocenter and 6 patients with larger PTV needed 10-ipsi-lateral-arcs at two-isocenters separated by 5-8cm. Bilateral targets were independently planned with 6-arcs for each target with its own isocenter. All plans optimized using Eclipse-TPS to deliver 50.4 Gy to PTVs while sparing the surrounding OARs (lungs, heart, thyroid, spinal-cord, esophagus etc.). Patient-specific Quality-Assurance (PSQA) tests were performed for the HalcyonPlans using ionization-chamber, film, MatriXX, Delta4, ArcCheck and Portal-dosimetry. Gamma pass rates at 3%/3mm, 3%/2mm and 2%/2mm were evaluated.
Results: The HalcyonPlans improved the PTV coverage by increasing %VRx by 10.6% for LeftPTV and 8.2% for RightPTV. HalcyonPlans reduced the heart mean-dose by 2Gy and V20Gy, V10Gy and V5Gy volumes by 30cc, 74cc and 87cc, respectively. Left-lung sparing was better in the HalcyonPlans but right lung V10Gy was increased by 5.7%. Dose to other OARs were comparable. Average delivery-times were <3 minutes for single-isocenter plans (118MUs/arc) and <5 minutes for dual-isocenters plans (96MUs/arc). Average deviation of -1.5%Â±0.8% was observed from the ionization-chamber measurements. The average %gamma pass rates at 3%/3mm were 96.2Â±2.8, 95.1Â±1.9, 99.3Â±0.6, 100.0Â±0.0 and 100.0Â±0.0 for film, MatriXX, ArcCheck, Delta4 and Portal-dosimetry, respectively.
Conclusion: Halcyon plans provided better dose coverage while allowing greater sparing of heart and left lung from doses associated with increased risk for complications and the delivery accuracy was acceptable.
Funding Support, Disclosures, and Conflict of Interest: Varian Medical Systems grant