Incorporating geometric ray tracing to generate initial conditions for intensity modulated arc therapy optimization

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Intensity Modulated Arc Therapy (IMAT) is an advanced radiotherapy technique, a rotational form of Intensity Modulated Radiation Therapy (IMRT).
• IMAT involves dynamic adjustments of multileaf collimator (MLC) positions during gantry rotation, enabling precise dose delivery.
• Efficient generation of initial IMAT plans is crucial for optimizing treatment outcomes and reducing planning time.

Purpose of the Study:

• To describe a novel method for generating Intensity Modulated Arc Therapy (IMAT) plans.
• To utilize a fast ray tracing technique for initial multileaf collimator (MLC) leaf positioning before final optimization.
• To improve the efficiency and efficacy of IMAT plan generation.

Main Methods:

• A three-step process was employed: anatomical arc generation, Ray Importance Factor (RIF) map generation via ray tracing for MLC modification, and Leaf Position Optimization (LPO).
• RIF maps were used to reduce maximum doses within the planning target volume (PTV) and improve dose to low-dose voxels.
• The method was validated on phantom cases (prostate and head and neck) and compared with Intensity Modulated Radiation Therapy (IMRT).

Main Results:

• Incorporating RIF and LPO significantly reduced the objective function values by up to 52% compared to LPO alone.
• The IMAT plan for the head and neck phantom demonstrated comparable target dose coverage to IMRT.
• The IMAT plan achieved a slightly lower dose to normal tissues compared to a conventional six-field IMRT plan.

Conclusions:

• The Ray Importance Factor (RIF) method efficiently generates initial IMAT arcs.
• This approach facilitates further multileaf collimator (MLC) leaf position optimization for more favorable IMAT treatment plans.
• The developed method offers a promising strategy for enhancing IMAT plan quality and efficiency.