Halcyon clinical performance evaluation: A log file-based study in comparison with a C-arm Linac.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Volumetric Modulated Arc Therapy (VMAT) is a crucial radiotherapy technique.
• Advancements in Treatment Delivery Systems (TDS) aim to improve accuracy and efficiency.
• Comparing new ring-shaped TDS with conventional C-arm linear accelerators (Linacs) is essential for clinical adoption.

Purpose of the Study:

• To compare the dosimetric and mechanical accuracy of VMAT delivery between the Halcyon TDS and a conventional C-arm Linac.
• To evaluate the impact of mechanical parameter fluctuations on dosimetric accuracy.
• To assess the performance of a novel ring-shaped TDS in a clinical setting.

Main Methods:

• Log file analysis of clinically delivered VMAT fractions from Halcyon and TrueBeam Linacs.
• Extraction and analysis of mechanical parameters, including Multi-Leaf Collimator (MLC) leaf errors and gantry angle accuracy.
• Dose recalculations incorporating mechanical parameter fluctuations to evaluate Dose Volume Parameters (DVP).

Main Results:

• Halcyon and TrueBeam demonstrated comparable MLC leaf positioning accuracy (mean RMS errors of 0.028 mm and 0.031 mm, respectively).
• Halcyon exhibited superior gantry angle accuracy (0.035° mean RMS error) compared to TrueBeam (0.065°).
• Both systems showed similar levels of dose-volume parameter variations (approx. 0.1%) due to mechanical errors, but Halcyon had lower DVP standard deviations.

Conclusions:

• The Halcyon TDS achieves mechanical accuracy comparable to the TrueBeam TDS while delivering VMAT at double the speed.
• The Halcyon TDS demonstrates potentially superior dosimetric accuracy, evidenced by lower DVP standard deviations.
• The ring-shaped design of the Halcyon contributes to its enhanced gantry angle precision.