WE‐E‐134‐03: Ultrasonic Tissue Characterization of Parotid‐Gland Injury Following Head‐And‐Neck Radiotherapy Using Nakagami‐Parameter Imaging: A Feasibility Study

Abstract

Purpose: Radiotherapy (RT) is an important modality in the multidisciplinary approach to treating head‐and‐neck malignancies. However, xerostomia (dry mouth), secondary to parotid‐gland injury, is a distressing side‐effect affecting up to 90% of patients post head‐and‐neck RT. The purpose of this study is to develop an ultrasonic tissue characterization technique based on Nakagami‐parameter imaging to evaluate parotid‐gland injury. Methods: A preliminary clinical study was conducted with 12 post‐RT patients and 12 healthy volunteers. Each participant underwent one ultrasound study in which ultrasound scans were performed in the longitudinal, i.e. vertical, orientation on the bilateral parotids. For the 12 patients, the mean radiation dose to the parotid glands was 37.7 ± 9.5 Gy, and the mean follow‐up time was 16.3 ± 4.8 months. All enrolled patients experienced grade 1 or 2 late salivary‐gland toxicity (RTOG/EORTC morbidity scale). The normal parotid glands served as the control group. From Nakagami imaging, Nakagami scaling and shape parameters were computed from the RF data to quantify radiation‐induced parotid‐gland changes. Results: Significant differences in Nakagami parameters were observed between the normal and post‐RT parotid glands. The mean Nakagami scaling parameter values were (3.77 ± 1.70)10E8 for the normal parotid glands, and (2.77 ± 1.69)10E8 for the irradiated parotid glands (p<0.001). The mean Nakagami shape parameter values were 2.16 ± 0.95 for the normal parotid glands, and 1.29 ± 0.68 for the irradiated parotid glands (p<0.001). Radiation‐induced parotid‐gland injury appears to be associated with decreased Nakagami parameters. Conclusion: In this study, we demonstrate the feasibility of using Nakagami parameters to evaluate parotid‐gland injury. Nakagami imaging, which complements conventional B‐mode imaging, has the potential of providing key imaging signatures for ultrasonic characterization of radiation‐induced changes in the parotid glands. This imaging method may be useful as we try to address xerostomia in patients following radiotherapy for head‐and‐neck malignancies.