Improved stratification algorithms for step-and-shoot MLC delivery in intensity-modulated radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• Intensity-modulated radiotherapy (IMRT) involves complex optimization processes to determine beam fluence distributions.
• Delivering IMRT plans requires transforming fluence maps into sequences of subsegments for multileaf collimator (MLC) motion.
• Stratification, a key step in this process, reduces fluence map complexity by assigning discrete intensity values to beamlets.

Purpose of the Study:

• To formally introduce and evaluate different concepts of stratification for step-and-shoot IMRT delivery.
• To propose and validate a novel dose-oriented stratification principle that minimizes the error in the resulting dose distribution.
• To compare the proposed method against existing intensity-minimizing strategies.

Main Methods:

• Formal introduction of various stratification concepts for step-and-shoot delivery.
• Development of an original stratification algorithm focused on minimizing dose distribution error.
• Comparison of the dose-oriented stratification with intensity-based stratification methods.

Main Results:

• The proposed dose-oriented stratification method achieves a better approximation of the original, unsequenced IMRT plan.
• This improvement is observed for a comparable total number of subsegments used in the delivery sequence.
• The new algorithm demonstrates effectiveness in approximating the intended radiation dose.

Conclusions:

• Dose-oriented stratification offers a superior approach for approximating IMRT plans in step-and-shoot delivery compared to intensity-based methods.
• The presented algorithm can be integrated into existing sequencing programs for IMRT treatment planning.
• This method is also applicable to interpolated plans generated during multicriteria inverse planning.