The ArcCHECK diode array for dosimetric verification of HybridArc

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• HybridArc is an advanced radiotherapy technique combining dynamic conformal arcs with inverse planning.
• Accurate dose calculation is crucial for effective and safe radiation delivery in complex treatment modalities.

Purpose of the Study:

• To assess the dosimetric accuracy of the HybridArc treatment planning system (iPlan RT Dose 4.5).
• To compare the performance of Monte Carlo (MC) and Pencil Beam (PB) dose algorithms for HybridArc plans.
• To evaluate HybridArc plans for both intracranial and extracranial sites.

Main Methods:

• HybridArc plans were created for various anatomical sites.
• Plans were recalculated using MC and PB algorithms in iPlan RT Dose.
• Dosimetric measurements were performed using a four-dimensional diode array (ArcCHECK) and an ionization chamber with a Novalis accelerator (6 MV).
• Calculated and measured dose distributions were compared using 2% dose difference and 2 mm distance-to-agreement criteria.

Main Results:

• Monte Carlo (MC) algorithm calculations showed good agreement with ArcCHECK measurements for HybridArc plans.
• Pencil Beam (PB) algorithm calculations demonstrated significant differences compared to ArcCHECK measurements.
• The MC algorithm was found to be superior to the PB algorithm for HybridArc plan calculations.
• A large arc step size (10°) in PB calculations was identified as a potential limitation.

Conclusions:

• The Monte Carlo (MC) algorithm provides accurate dose calculations for the HybridArc treatment modality.
• The Pencil Beam (PB) algorithm is less suitable for HybridArc dose calculations, necessitating improvements in angular resolution.
• HybridArc shows dosimetric accuracy suitable for clinical implementation when planned and calculated with appropriate algorithms.