2-Step IMAT and 2-Step IMRT: a geometrical approach

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Intensity Modulated Arc Therapy (IMAT) and Intensity Modulated Radiotherapy (IMRT) are advanced radiation techniques.
• Concave target volumes and organs at risk (OARs) present challenges in treatment planning, often requiring complex segmentations.

Purpose of the Study:

• To develop a novel method for reducing treatment segments in IMAT and IMRT for concave target volumes.
• To optimize segment widths and weights using geometric considerations, aiming for minimal intensity levels per OAR.

Main Methods:

• A geometric and topological approach was used, adapting Brahme's model for an annular target surrounding a circular OAR.
• A single additive segment with optimized width and weight was employed, minimizing root mean square (rms) error and ensuring zero dose to the OAR.

Main Results:

• The 'optimized 2-Step IMAT' method improved rms error by a factor of 4 compared to simple OAR blocking.
• Reduced rms error below 3% for cases with specific OAR-TV gaps, demonstrating enhanced dose accuracy.

Conclusions:

• The developed 'optimized 2-Step IMAT' and '2-Step IMRT' methods offer efficient segment reduction for complex target volumes.
• These findings are applicable to various arc therapy techniques and can inform adaptive radiotherapy strategies.