Efficient optimization of R50% when planning multiple cranial metastases simultaneously in single isocenter SRS/SRT.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• Simultaneous optimization of multiple cranial Planning Target Volumes (PTVs) presents significant challenges.
• Dose falloff, quantified by metrics like R50%, is variable and influenced by PTV characteristics, particularly volume.
• Existing literature lacks clear guidance on prospectively setting optimization constraints for desired R50% outcomes.

Purpose of the Study:

• To develop a quantitative method for translating desired R50% dose falloff into specific optimization structure constraints.
• To provide guidance for optimizing multiple PTVs with varying sizes and locations in cranial radiotherapy.
• To enable efficient production of acceptable treatment plans meeting specific R50% goals.

Main Methods:

• Derived an equation linking desired R50% goals and PTV volume to optimization structure size.
• Developed optimization schemas to achieve individual R50% goals for all PTVs.
• Validated the methodology using standard radiotherapy treatment planning software and equipment.

Main Results:

• Successfully demonstrated a method to prospectively determine optimization shell constraints based on PTV volume and R50% goals.
• Achieved or approached desired R50% outcomes for individual PTVs within a multi-PTV cranial plan.
• The proposed equation provides clear, quantitative guidance for treatment planners.

Conclusions:

• The developed methodology offers a practical solution for optimizing dose falloff in complex cranial radiotherapy plans.
• This approach facilitates the creation of more consistent and predictable treatment plans by controlling R50%.
• The findings support improved radiotherapy planning by providing objective criteria for optimization.