Jaws-only IMRT using direct aperture optimization

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Intensity modulated radiotherapy (IMRT) typically requires a multileaf collimator (MLC) for precise dose delivery.
• Clinics without MLCs face limitations in offering advanced IMRT techniques.
• Developing alternative IMRT delivery methods is crucial for broader accessibility.

Purpose of the Study:

• To develop and evaluate a novel "jaws-only" inverse planning approach for IMRT.
• To demonstrate the feasibility of generating conformal IMRT plans using only rectangular apertures and beam weights.
• To assess the clinical applicability and delivery efficiency of this MLC-free IMRT method.

Main Methods:

• Implemented an inverse planning approach using direct aperture optimization.
• Optimized jaw positions and aperture weights for rectangular field shapes.
• Incorporated jaw constraints directly into the optimization process, eliminating the need for leaf sequencing.
• Validated treatment plans on five patient cases (pancreas, breast, prostate) and delivered them to a phantom for dose measurements.

Main Results:

• Developed efficient "jaws-only" IMRT plans requiring 15-20 apertures per beam direction for conformal coverage.
• Achieved high degrees of intensity modulation using only rectangular field shapes.
• Phantom dose measurements confirmed the accuracy of the generated plans.
• Demonstrated a typical treatment delivery time of 18 minutes.

Conclusions:

• The "jaws-only" approach enables efficient IMRT plan generation and delivery without an MLC.
• This method provides a viable alternative IMRT option for radiation oncology departments lacking MLC technology.
• The direct aperture optimization technique simplifies the planning process by removing the need for leaf sequencing.