Control-point-specific plan robustness in volumetric modulated arc therapy-based cranial radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Intrafraction patient motion can degrade radiotherapy plan quality.
• Identifying motion-sensitive control points is crucial for mitigating these effects.
• Robust planning strategies aim to improve dosimetry and reduce planning target volume (PTV) margins.

Purpose of the Study:

• To enhance radiotherapy plan robustness against intrafraction motion by identifying control-point-specific dosimetric sensitivities.
• To retrospectively assess the impact of simulated patient motion on cranial radiotherapy plans.
• To explore control-point-specific plan characteristics influencing dosimetry.

Main Methods:

• Thirty cranial volumetric modulated arc therapy (VMAT) plans were converted to static field plans.
• Simulated intrafraction motion traces (n=100) were applied using a MATLAB application.
• Planning target volume (PTV) coverage and gross tumor volume (GTV) dose metrics were analyzed; control point dose-volume histograms (DVHs) were assessed using area under the curve (AUC) analysis.

Main Results:

• Simulated intrafraction motion led to PTV coverage loss in 78.6% of motion traces, with no significant changes in GTV D99%.
• Multileaf collimator (MLC) aperture areas showed weak to moderate correlations with standard deviation of AUC (sAUC).
• Two distinct subpopulations of MLC aperture areas were identified based on mean AUC (mAUC) thresholds.

Conclusions:

• The dosimetric impact of intrafraction motion is linked to the sensitivity of specific control points.
• Targeting motion-sensitive control points for gating could improve robustness and dosimetry, supporting PTV margin reduction.
• Cranial radiotherapy plans are suitable for control-point-level motion analysis, with potential expansion to other anatomical sites.