Characterization of Ethos therapy systems for adaptive radiation therapy: A multi-machine comparison

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• The Ethos therapy system enables online CBCT-guided adaptive radiation therapy.
• Clinical implementation of multiple systems necessitates machine characterization and variation quantification for patient interchangeability.
• Limited vendor-independent data exists on Ethos machine performance.

Purpose of the Study:

• To characterize dosimetric and mechanical features of Ethos machines.
• To quantify variations between individual Ethos machines.
• To provide vendor-independent performance data.

Main Methods:

• Six Ethos machines with 6-MV FFF beams were characterized.
• Point doses, profiles, and dose distributions were measured and compared to vendor data and calculations.
• Key parameters quantified include leaf transmission, DLG, couch attenuation, isocenter accuracy, and kV-MV coincidence.
• 1D and 3D gamma analysis was used to assess agreement.

Main Results:

• Excellent agreement was observed between measurements and vendor data/dose calculations (mean γ1%/1mm < 0.30).
• All machines demonstrated consistent performance in profiles, point measurements, and dose distributions.
• Minimal machine variations were found for DLG (0.05 mm), leaf transmission (0.001%), isocenter accuracy (0.08 mm), kV-MV coincidence (0.15 mm), couch attenuation (0.69%), and CBCT dose (0.29 mGy).

Conclusions:

• Ethos therapy systems exhibit excellent agreement with vendor data and pre-configured beam models.
• High consistency was demonstrated across all tested machines.
• These findings establish benchmark data for the clinical introduction of Ethos systems.