Continuous intensity map optimization (CIMO): a novel approach to leaf sequencing in step and shoot IMRT.

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Imaging

Background:

• Intensity modulated radiation therapy (IMRT) often requires a large number of beam segments for accurate dose delivery.
• Optimizing leaf sequencing is crucial for reducing treatment time and improving plan quality in IMRT.

Purpose of the Study:

• To introduce and evaluate a novel leaf-sequencing approach, continuous-intensity-map-optimization (CIMO), for reducing beam segments in IMRT.
• To assess the impact of CIMO on treatment plan quality, including target dose uniformity and intensity map accuracy.

Main Methods:

• Developed the CIMO algorithm using a simulated annealing approach to minimize differences between optimized and sequenced intensity maps.
• Applied CIMO to ten clinical IMRT cases across various tumor sites (head-and-neck, pancreas, prostate, brain, pelvis).
• Compared CIMO performance against Pinnacle3's leaf sequencer and the power-of-two algorithm, considering multileaf collimator constraints.

Main Results:

• CIMO achieved an average 54% reduction in beam segments compared to Pinnacle3's leaf sequencer.
• Plans sequenced with CIMO demonstrated improved target dose uniformity and reduced intensity map discrepancies.
• Significant segment reductions were observed with Varian (26%) and Elekta (67%) multileaf collimators, with rapid sequencing times (<1 minute/beam).

Conclusions:

• The CIMO algorithm offers a substantial reduction in beam segments for IMRT, enhancing treatment efficiency.
• CIMO optimizes aperture shapes and weights simultaneously, leading to improved plan quality.
• This approach presents a promising advancement for step-and-shoot IMRT delivery.