Dir-based dose accumulation for parotid glands in head and neck cancer: Accuracy and implications for adaptive...

Deformable image registration (DIR) is widely utilized for dose accumulation, but errors in image registration can compromise its accuracy. This study evaluated the precision of DIR in dose accumulation for parotid gland and proposed a method to correct errors induced by DIR.

This retrospective study included 123 patients with head and neck cancer. For each patient, the accumulated mean dose (D_mean) to the parotid gland was obtained by manual segmentation (ground truth) and two DIR strategies: contour propagation and dose mapping. The normal tissue complication probability (NTCP) model predicting xerostomia was employed to translate accumulated D_mean into NTCP values. Comparisons were made between ground truth and DIR for accumulated D_mean and NTCP.

The maximum discrepancy of accumulated D_mean and NTCP between DIR and ground truth was 4.87 Gy and 3.94 %, respectively. The discrepancies of accumulated D_mean between DIR and ground truth were significantly correlated with the discrepancies between accumulated D_mean of ground truth and nominal D_mean. Mid-treatment weekly D_mean discrepancies between contour propagation and manual segmentation showed the capability to correct the accumulated D_mean of DIR and decrease the error of NTCP prediction from 2.89 % and 3.81 % to 1.26 % and 2.04 % for baseline xerostomia Grade 0 and Grade 1-2, respectively.

Significant discrepancies were observed in accumulated D_mean of parotid glands between DIR and manual segmentation in candidates for adaptive radiotherapy. Utilizing mid-treatment CT scans offers a practical solution to correct DIR-induced errors, improving the accuracy of dose accumulation.