  Purpose: This study aims to quantify the variation in dose-volume histogram
(DVH) and normal tissue complication probability(NTCP) metrics for
head-and-neck (HN) cancer patients when alternative organ-at-risk(OAR)
delineations are used for treatment planning and for treatment plan evaluation.
We particularly focus on the effects of daily patient positioning/setup
variations(SV) in relation to treatment technique and delineation variability.
  Materials and Methods: We generated two-arc VMAT, 5-beam IMRT, and 9-beam
IMRT treatment plans for a cohort of 209 HN patients. These plans incorporated
five different OAR delineation sets, including manual and four automated
algorithms. Each treatment plan was assessed under various simulated
per-fraction patient setup uncertainties, evaluating the potential clinical
impacts through DVH and NTCP metrics.
  Results: The study demonstrates that increasing SV generally reduces
differences in DVH metrics between alternative delineations. However, in
contrast, differences in NTCP metrics tend to increase with higher setup
variability. This pattern is observed consistently across different treatment
plans and delineator combinations, illustrating the intricate relationship
between SV and delineation accuracy. Additionally, the need for delineation
accuracy in treatment planning is shown to be case-specific and dependent on
factors beyond geometric variations.
  Conclusions: The findings highlight the necessity for comprehensive Quality
Assurance programs in radiotherapy, incorporating both dosimetric impact
analysis and geometric variation assessment to ensure optimal delineation
quality. The study emphasizes the complex dynamics of treatment planning in
radiotherapy, advocating for personalized, case-specific strategies in clinical
practice to enhance patient care quality and efficacy in the face of varying SV
and delineation accuracies.
