Auto-segmentation of neck nodal metastases using self-distilled masked image transformer on longitudinal MR images.

OBJECTIVES: Auto-segmentation promises greater speed and lower inter-reader variability than manual segmentations in radiation oncology clinical practice. This study aims to implement and evaluate the accuracy of the auto-segmentation algorithm, "Masked Image modeling using the vision Transformers (SMIT)," for neck nodal metastases on longitudinal T2 -weighted (T2 w) MR images in oropharyngeal squamous cell carcinoma (OPSCC) patients.

METHODS: This prospective clinical trial study included 123 human papillomaviruses (HPV-positive [+]) related OSPCC patients who received concurrent chemoradiotherapy. T2 w MR images were acquired on 3 T at pre-treatment (Tx), week 0, and intra-Tx weeks (1-3). Manual delineations of metastatic neck nodes from 123 OPSCC patients were used for the SMIT auto-segmentation, and total tumor volumes were calculated. Standard statistical analyses compared contour volumes from SMIT vs manual segmentation (Wilcoxon signed-rank test [WSRT]), and Spearman's rank correlation coefficients ( ρ ) were computed. Segmentation accuracy was evaluated on the test data set using the dice similarity coefficient (DSC) metric value. P -values <0.05 were considered significant.

RESULTS: No significant difference in manual and SMIT delineated tumor volume at pre-Tx (8.68 ± 7.15 vs 8.38 ± 7.01 cm3 , P  = 0.26 [WSRT]), and the Bland-Altman method established the limits of agreement as -1.71 to 2.31 cm3 , with a mean difference of 0.30 cm3 . SMIT model and manually delineated tumor volume estimates were highly correlated ( ρ = 0.84-0.96, P  < 0.001). The mean DSC metric values were 0.86, 0.85, 0.77, and 0.79 at the pre-Tx and intra-Tx weeks (1-3), respectively.

CONCLUSIONS: The SMIT algorithm provides sufficient segmentation accuracy for oncological applications in HPV+ OPSCC.

ADVANCES IN KNOWLEDGE: First evaluation of auto-segmentation with SMIT using longitudinal T2 w MRI in HPV+ OPSCC.