Author: Michalis Aristophanous, Steven Blum, Laura I. Cervino, Antonio L. Damato, Karen Episcopia, Chi Huang, Shih-Chi Lin, Michelle K. Savacool 👨🔬
Affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, Memorial Sloan Kettering Cancer Center 🌍
Purpose: Varian Ethos (Varian Medical Systems, Palo Alto, CA) is a 6 MV flattening-filter-free (FFF) only machine, posing a challenge in creating homogeneous dose distributions when using manual 3D-CRT techniques. EZFluenceTM (Radformation Inc, New York, NY) is a software that aims to create uniform dose distributions using electronic compensator-based optimal fluences or field-in-field techniques. This work discusses the commissioning effort of electronic compensator-based EZFluence plans for this machine.
Methods: In phase 1, to compare EZFluence plans to manually-created plans, six clinical reference plans (with flattening filter, 6 or 15 MV per institutional standard, planned by expert dosimetrist) representing clinical practice were identified. Keeping identical beam geometry and physician blocking, EZFluence was used to generate plans on Ethos. The resulting dose distributions were compared to reference plans for max dose, PTV D95% and PTV V100%. In phase 2, four ex-novo EZFluence Ethos plans, with at least 2 fields, covering a range of dose/fraction, field sizes, and sites, were generated, evaluated, and delivered. Secondary dose calculations and Gamma Analyses were performed with patient anatomy using commercially available software. Measurements were performed using two commercially available detector arrays.
Results: EZFluence produced FFF plans with dose distributions that were deemed clinically acceptable by expert physics review. For phase 1 plans, the max dose was ≤111.3% except when the patient separation was large enough requiring a higher energy in the reference plan. For all plans, the PTV D95% was ≥97.1% and the PTV V100% was ≥87.9%. For phase 2 plans, the secondary dose calculation software reported Gamma pass rates ≥92.1%. The detector array-based measurement Gamma Analysis for each ex-novo plan was ≥95.0%.
Conclusion: EZFluence can produce clinically acceptable and deliverable 3D-CRT plans on Ethos. Patients with large separation may not be well-suited for a 6 MV-only machine due to high max dose.