SU-E-J-220: Evaluation of Atlas-Based Auto-Segmentation (ABAS) in Head-And-Neck Adaptive Radiotherapy

Authors


Abstract

Purpose:

Evaluate the accuracy of atlas_based auto segmentation of organs at risk (OARs) on both helical CT (HCT) and cone beam CT (CBCT) images in head and neck (HN) cancer adaptive radiotherapy (ART).

Methods:

Six HN patients treated in the ART process were included in this study. For each patient, three images were selected: pretreatment planning CT (PreTx_HCT), in treatment CT for replanning (InTx_HCT) and a CBCT acquired in the same day of the InTx_HCT. Three clinical procedures of auto segmentation and deformable registration performed in the ART process were evaluated: a) auto segmentation on PreTx_HCT using multi_subject atlases, b) intra_patient propagation of OARs from PreTx_HCT to InTx_HCT using deformable HCT_to_HCT image registration, and c) intra_patient propagation of OARs from PreTx_HCT to CBCT using deformable CBCT_to_HCT image registration. Seven OARs (brainstem, cord, L/R parotid, L/R submandibular gland and mandible) were manually contoured on PreTx_HCT and InTx_HCT for comparison. In addition, manual contours on InTx_CT were copied on the same day CBCT, and a local region rigid body registration was performed accordingly for each individual OAR. For procedures a) and b), auto contours were compared to manual contours, and for c) auto contours were compared to those rigidly transferred contours on CBCT. Dice similarity coefficients (DSC) and mean surface distances of agreement (MSDA) were calculated for evaluation.

Results:

For procedure a), the mean DSC/MSDA of most OARs are >80%/±2mm. For intra_patient HCT_to_HCT propagation, the Resultimproved to >85%/±1.5mm. Compared to HCT_to_HCT, the mean DSC for HCT_to_CBCT propagation drops ∼2–3% and MSDA increases ∼0.2mm. This Resultindicates that the inferior imaging quality of CBCT seems only degrade auto propagation performance slightly.

Conclusion:

Auto segmentation and deformable propagation can generate OAR structures on HCT and CBCT images with clinically acceptable accuracy. Therefore, they can be reliably implemented in the clinical HN ART process.

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