Standardising Radiotherapy Treatment Planning: The Role of Plan Complexity
Abstract
Purpose
Most radiotherapy procedures follow standardized protocols to ensure quality. However, treatment planning and optimization still remain insufficiently standardized. This study evaluates the potential of incorporating plan complexity controls within class solution methodologies for reducing variability and improving the standardization of treatment planning across anatomical sites and delivery platforms.
Methods
VMAT plans were generated in Eclipse for lung stereotactic body radiotherapy (SBRT), stereotactic radiosurgery (SRS), and prostate with lymph node involvement. Plans were created for TrueBeam (all sites) and Halcyon (prostate). A three-stage optimization strategy was applied: (i) Off (no complexity control), (ii) ASC (Aperture Shape Controller set to Moderate), and (iii) MU (ASC plus monitor-unit limitation). Plans were required to remain dosimetrically equivalent using site-specific clinical acceptance criteria and were compared to assess variability and the impact of complexity control. Plan parameters and complexity were quantified using monitor units per cGy (MU/cGy), Plan Aperture Modulation (PAM), Plan Irregularity (PI), and Average Leaf Pair Opening (ALPO). Mean values, standard deviations, and relative differences were analyzed. ANOVA testing was applied to assess statistical significance.
Results
ASC alone produced modest metric improvements and limited variability reduction, with negligible impact on Halcyon. In contrast, MU limitation significantly improved all metrics for all sites/platforms. Reductions of ~35–50% in MU/cGy and ~60–90% in PAM were observed, with decreases in PI and increases in ALPO, consistent with simpler and more regular beam apertures. Inter-plan variability decreased consistently at the MU stage for all metrics and sites; all MU-stage changes were significant (p < 0.01), indicating plan aperture control as the dominant driver of variability reduction and harmonization.
Conclusion
Complexity management integrated into class solutions significantly reduced treatment-plan variability within treatment sites and across treatment platforms, while preserving dosimetric equivalence. Complexity metrics provide a quantitative framework for standardizing and harmonizing radiotherapy treatment planning.