Abstract
Field size limitations on Halcyon and Ethos treatment machines largely preclude use of the conventional monoisocentric three-field technique for breast/chest wall and regional lymph nodes. We present an alternative, IMRT-based planning approach that facilitates treatment on Halcyon and Ethos while preserving plan quality. Eight breast and regional node cases (four left-sided, four right-sided) were planned for an Ethos machine using a 15-17 field IMRT technique. Institutional plan quality metrics for CTV and PTV coverage and OAR sparing were assessed. Five plans (four right-sided, one left-sided) were also planned using a hybrid 3D multisocenter technique. CTV coverage and OAR sparing were compared to the IMRT plans. Eclipse scripting tools were developed to aid in beam placement and plan evaluation through a set of dosimetric scorecards, and both are shared publicly. On average, the IMRT plans achieved breast CTV and PTV coverage at 50Gy of 97.9% and 95.7%, respectively. Supraclavicular CTV and PTV coverages at 45Gy were 100% and 95.5%. Axillary lymph node CTV and PTV coverages at 45Gy were 100% and 97.1%, and IMN CTV coverage at 45Gy was 99.2%. Mean ipsilateral lung V20 Gy was 19.3%, and average mean heart dose was 1.6Gy for right-sided cases and 3.0Gy for left-sided. In comparison to the hybrid 3D plans, IMRT plans achieved higher breast and supraclavicular CTV coverage (99.9%vs. 98.6% and 99.9%vs. 93.4%), higher IMN coverage (99.6%vs. 78.2%), and lower ipsilateral lung V20 Gy (19.6%vs. 28.2%). Institutional plan quality benchmarks were achieved for all eight cases using the IMRT-based planning approach. The IMRT-based planning approach offered superior conformity and OAR sparing than a competing hybrid 3D approach.
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