Leaf sequencing with secondary beam blocking under leaf positioning constraints for continuously modulated...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Generating arbitrary photon fluence patterns is crucial for intensity modulated radiotherapy (IMRT).
• Existing methods often assume discrete beam modulation or do not adequately address minimum leaf separation constraints in multileaf collimators (MLCs).

Purpose of the Study:

• To develop a method for creating arbitrary photon fluence patterns for IMRT using MLCs with minimum leaf separation requirements.
• To address the limitations of discrete modulation by enabling continuous or infinitely small bixel modulation.

Main Methods:

• The proposed method adapts the time-optimal solution by Spirou-Stein-Svensson, initially disregarding minimum gap requirements.
• Secondary beam blocking devices, specifically two computer-controlled orthogonal backup diaphragms, are employed to restore leaf separation and prevent overexposure.
• The efficacy of both vertical (parallel to leaf motion) and horizontal (perpendicular to leaf motion) backup diaphragms is investigated.

Main Results:

• The method accurately delivers desired photon fluence modulation while adhering to MLC leaf positioning constraints.
• The use of secondary beam blocking effectively manages overexposure risks associated with leaf separation.
• Demonstrated ability to generate zero fluence regions using combined horizontal and vertical backup diaphragms.

Conclusions:

• The developed method offers an accurate and feasible approach for generating complex photon fluence patterns in IMRT.
• It effectively overcomes the challenge of minimum leaf separation in MLCs through the intelligent use of secondary blocking devices.
• This technique enhances the precision and safety of radiotherapy delivery.