(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Standardize breast treatment planning techniques and provide class solution for delivery and inter- and/or intra-fraction motion management on Varian Halcyon/Ethos.
Methods: Retrospective randomized planning study consisting of 10 breast patients (5 left sided, 5 right sided) and chest-wall/nodal (axilla, SCF, IMC) was performed. Patients were treated in free-breathing and planned in Varian Eclipse v15.6, comparing bowtie-VMAT on Halcyon v2.0 to hybrid-tangential delivery (IMRT/VMAT) on Varian Trilogy. Treatment deliverability and accuracy was evaluated prospectively via combination of patient-specific pre-treatment QA and, for chest-wall/nodal patients, in-vivo EBT3 film on skin under bolus. To evaluate advantages of Halcyon’s daily CBCT setup, a prospective image guidance study of 10 patients treated on Trilogy was performed in which 3D-CBCT was routinely obtained in addition to the initial 2D-kV/kV image match. Finally, feasibility of inter- and intra-fraction motion management using the class bowtie solution was assessed for the first whole-breast patient treated after upgrading Halcyon to Ethos.
Results: Bowtie-VMAT on Halcyon was found to give dose distributions of uncompromising quality compared to Trilogy, with added benefits being: single energy (no 18X base plans), single optimization (no tangential-3DCRT/IMRT base plans), junction-free and with an approx. 5min appointment time saving. Patient-specific QA passed within standard 3%/3mm gamma criteria, and in-vivo dosimetry results showed agreement to plan within ± 5%. Use of daily CBCT match reduced setup errors by 2-3mm for nodal patients where sternum (primary surrogate for IMC) is not easily distinguished by kV planar imaging. Inter-fraction motion management was realized by applying Ethos Adaptive pathway, whilst intra-fraction cine EPID monitoring of patient chest-wall position (relative to plan) was within 5mm CTV-PTV margin.
Conclusion: Bowtie-VMAT as a class-solution for breast radiotherapy on Halcyon/Ethos was realized. The advanced image guidance/motion management and planning strategies have potential to reduce margins for better sparing of dose-limiting OARs (heart/lung).
Keywords
Breast, Radiation Therapy, Validation
Taxonomy
Not Applicable / None Entered.
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