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

BACKGROUND AND PURPOSE

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.

MATERIALS AND METHODS

This retrospective study included 123 patients with head and neck cancer. For each patient, the accumulated mean dose (D) 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 into NTCP values. Comparisons were made between ground truth and DIR for accumulated D and NTCP.

RESULTS

The maximum discrepancy of accumulated D and NTCP between DIR and ground truth was 4.87 Gy and 3.94 %, respectively. The discrepancies of accumulated D between DIR and ground truth were significantly correlated with the discrepancies between accumulated D of ground truth and nominal D. Mid-treatment weekly D discrepancies between contour propagation and manual segmentation showed the capability to correct the accumulated D 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.

CONCLUSIONS

Significant discrepancies were observed in accumulated D 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.