Treatment planning for volumetric modulated arc therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Volumetric modulated arc therapy (VMAT) is an advanced form of intensity-modulated radiation therapy (IMRT).
• VMAT involves continuous variations in gantry speed, multileaf collimator (MLC) position, and dose rate during treatment delivery.
• A novel treatment planning system for VMAT is presented to optimize radiation delivery.

Purpose of the Study:

• To introduce and evaluate a treatment planning system for VMAT.
• To compare VMAT plans with traditional segmental (step-and-shoot) IMRT.
• To assess the quality and delivery efficiency of VMAT across various cancer sites.

Main Methods:

• Developed a VMAT planning system using an iterative least-squares algorithm to generate fluence profiles at arc control points.
• Optimized solutions using direct-aperture optimization, considering MLC leaf motion constraints.
• Applied the method to five diverse clinical cases (lung, rectum, prostate, head and neck) and compared with segmental IMRT.

Main Results:

• VMAT achieved similar plan quality to IMRT for lung, prostate, and rectum cases, with delivery times up to four times faster.
• For prostate/pelvic nodes and head and neck cancers, VMAT reduced critical structure doses but resulted in longer delivery times.
• Treatment plans generally verified successfully, though complex cases like head and neck showed discrepancies between planned and measured doses.

Conclusions:

• VMAT planning systems can yield superior quality and/or faster delivery compared to IMRT, depending on treatment priorities.
• The presented VMAT planning approach has been successfully integrated into clinical workflows.
• VMAT represents a significant advancement in radiation therapy planning and delivery.