Dosimetric Evaluation of Ethos IMRT Versus Eclipse VMAT Plans for Cervical Cancer ART
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Purpose: The new Varian Ethos platform uses a clinical goal-based optimizer to generate IMRT/VMAT plans that can be used for online adaptive radiotherapy (ART). IMRT plans are preferred for ART as they optimize/calculate faster, thus reducing patients’ on-couch time. The purpose of this study was to establish a planning strategy for use with Ethos that can produce clinically acceptable IMRT plans for ART of cervical patients.
Methods: The Ethos optimizer automatically generates objectives from user-input goals, creates helper structures (e.g. rings, PTV-cropped organs), and adjusts the normal tissue objective (NTO) during optimization. We generated an Ethos planning template using goals based on our institution’s guidelines, a disease-specific RapidPlan DVH estimation model, and 12-field IMRT. We further lowered goal values for OARs (bladder, rectum, sigmoid and bowel) to match patient-specific RapidPlan DVH estimates. Eclipse VMAT plans were generated using the Photon Optimizer and our standard planning techniques including the same RapidPlan model and typical optimization structures (rings, etc). Both planning systems used AcurosXB. Radiation oncologists reviewed all plans for clinical acceptability. Mean dose for structures and global hotspots were evaluated to determine plan equivalence for five patients.
Results: All Ethos and Eclipse plans were approved by the radiation oncologist and had comparable plan quality, despite Ethos plans being template-based and faster to produce. PTV coverage was similar (VMAT PTV Dmean: 46.1Gy and IMRT PTV Dmean: 46.0Gy) for equivalent OAR sparing. Average mean doses for rectum, bladder, bowel and sigmoid for VMAT(IMRT) were 32.8Gy(33Gy), 34.9Gy(35.8Gy), 14.2Gy(15.5Gy), and 35.9Gy(35Gy), respectively. Global hotspots were marginally higher in VMAT(106.8%) versus IMRT(105.9%).
Conclusion: Safe, clinically acceptable IMRT plans can be generated by the Ethos TPS for cervical cancer ART. Using a standardized gynecological Ethos planning template allowed for efficient plan creation.
Funding Support, Disclosures, and Conflict of Interest: Kevin Moore acknowledges consulting fees and honoraria from Varian Medical Systems. Xenia Ray acknowledges Honoria and speaker fees from Varian Medical Systems and a research agreement with Varian Medical Systems. Kelly Kisling acknowledges Honoraria and speaker fees from Varian Medical Systems
Keywords
Dosimetry, Treatment Planning, Treatment Techniques
Taxonomy
TH- External Beam- Photons: adaptive therapy
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