Quadtrees as a representation for irregularly shaped fields in radiotherapy applications.

Area of Science:

• Medical Physics
• Computational Biology
• Radiotherapy

Background:

• Data representation significantly affects treatment planning accuracy and computation time.
• Irregularly shaped fields pose challenges for electron pencil-beam algorithms.

Purpose of the Study:

• To introduce the quadtree data structure for representing irregularly shaped fields in 3D electron pencil-beam algorithms.
• To evaluate the impact of the quadtree on dose calculation accuracy and computational efficiency.

Main Methods:

• Implemented a quadtree data structure to subdivide irregular fields into variable-sized pencil-beams.
• Focused smaller pencil-beams on field edges for enhanced penumbra region accuracy.
• Developed algorithms to simplify pencil-beam fluence evaluation and reduce systematic errors.

Main Results:

• The quadtree significantly reduced the number of pencil-beams required for dose calculation.
• Preserved or improved calculational accuracy, especially in penumbra regions.
• Achieved a tenfold performance improvement compared to alternative methods for irregular fields.

Conclusions:

• The quadtree is an effective data structure for optimizing electron pencil-beam treatment planning.
• It enhances computational speed without compromising accuracy for complex field shapes.
• Quadtree implementation offers a substantial advancement in radiotherapy treatment planning efficiency.