Correlation of contouring variation with modeled outcome for conformal non-small cell lung cancer radiotherapy.

Abstract

Contouring variation is a well know uncertainty in modern radiotherapy. This study investigates the relationship between contouring variation, tumor control probability (TCP) and equivalent uniform dose (EUD) for conformal non-small cell lung cancer (NSCLC) radiotherapy. Seven patients were retrospectively recruited to the study and multiple PTV contours were generated based on CT and PET imaging by three observers. Plans were created for each PTV volume. Volumes were analyzed geometrically using volume, location, dimension and conformity index (CI). Radiobiological plan analysis consisted of two TCP models and EUD. Spearman's correlation coefficient (ρ) was used to quantify the association between geometric variation and radiobiological metrics. The variation in CI and TCP for the study was 0.66-0.90% and 0.19-0.68%. Changes in lateral dimension and volume were significantly correlated with TCP and EUD with an average ρ of -0.49 and 0.43 (p<0.01) respectively. TCP and geometric contour variation show significant correlation. This correlation was most significant for changes in lateral dimensions of PTV volumes. This association may be used in the assessment of contouring protocol violations in multicenter clinical trials and aid in the design of future contouring studies.