Poster - 37: Pre-clinical geometric, dosimetric and timing assessment of head and neck OARs using an in-house atlas-based auto-segmentation (ABAS) tool

Purpose: This study aims to validate the geometric and dosimetric performance of our in-house ABAS tool using manual inter-observer variation as benchmark data. Materials and methods: An in-house ABAS constructed, using MIM MaestroTM version 6.5, from 36 previously treated head and neck cases. 15 OARs of eight nasopharynx patients were segmented via three observers from the same institution and using the in-house ABAS. Percentage of volume differences (ΔV%,), degree of overlap (DICE), distance-to-agreement and the standard deviation of absolute dose difference ΔD SD(Gy) among the eight cases [ΔDmax SD(Gy) for serial organs and ΔDmean SD(Gy) for parallel organs] were compared between the manual segmentation and original ABAS contours for each OAR. Results: The geometric results indicated that ABAS ΔV% was within 1SD from the manual segmentation. DICE showed that manual segmentation marginally outperformed ABAS in the delineation of parotid glands, submandibular glands, and laryngopharynx, but ABSA performed as well as the manual segmentation or better for all other structures. The distance-to-agreement was <1.5 cm for 87% of ABAS structures. From a dosimetric perspective, only ABAS salivary glands demonstrated higher ΔD SD(Gy) compared to manual segmentation. For all other structures ABAS results were similar or better than the manual segmentation. The average time to segment a complete H&N OAR set was <3minutes versus 30minutes for manual segmentation. Conclusion: ABAS is a practical time-saving tool. This study indicated up 90% time-saving of the operator time per case. ABAS geometric and dosimetric results were within ±1SD inter-observer variation for most of the structures.