Program Information

Gaussian Mixture Model Analysis of Radiation-Induced Parotid-Gland Injury: An Ultrasound Study of Acute and Late Xerostomia in Head-And-Neck Radiotherapy

T Liu

T Liu¹*, D Yu² , J Beitler³ , S Tridandapani⁴ , D Bruner⁵ , W Curran⁶ , X Yang⁷ , (1) Department of Radiation Oncology and Winship Cancer Institute, Emory Univ, Atlanta, GA, (2) Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA, (3) Department of Radiation Oncology and Winship Cancer Institute,Emory University, Atlanta, GA, (4) Department of Radiology and Imaging Sciences and Winship Cancer Institute,Emory University, Atlanta, GA, (5) School of Nursing and Winship Cancer Institute, Emory Univesity, Atlanta, GA, (6) Department of Radiation Oncology and Winship Cancer Institute,Emory University, Atlanta, GA, (7) Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA

Presentations

TH-E-BRF-9 Thursday 1:00PM - 2:50PM Room: Ballroom F

Purpose:Xerostomia (dry mouth), secondary to parotid-gland injury, is a distressing side-effect in head-and-neck radiotherapy (RT). This study’s purpose is to develop a novel ultrasound technique to quantitatively evaluate post-RT parotid-gland injury.

Methods:Recent ultrasound studies have shown that healthy parotid glands exhibit homogeneous echotexture, whereas post-RT parotid glands are often heterogeneous, with multiple hypoechoic (inflammation) or hyperechoic (fibrosis) regions. We propose to use a Gaussian mixture model to analyze the ultrasonic echo-histogram of the parotid glands. An IRB-approved clinical study was conducted: (1) control-group: 13 healthy-volunteers, served as the control; (2) acute-toxicity group - 20 patients (mean age: 62.5 ± 8.9 years, follow-up: 2.0±0.8 months); and (3) late-toxicity group - 18 patients (mean age: 60.7 ± 7.3 years, follow-up: 20.1±10.4 months). All patients experienced RTOG grade 1 or 2 salivary-gland toxicity. Each participant underwent an ultrasound scan (10 MHz) of the bilateral parotid glands. An echo-intensity histogram was derived for each parotid and a Gaussian mixture model was used to fit the histogram using expectation maximization (EM) algorithm. The quality of the fitting was evaluated with the R-squared value.

Results:(1) Control-group: all parotid glands fitted well with one Gaussian component, with a mean intensity of 79.8±4.9 (R-squared>0.96). (2) Acute-toxicity group: 37 of the 40 post-RT parotid glands fitted well with two Gaussian components, with a mean intensity of 42.9±7.4, 73.3±12.2 (R-squared>0.95). (3) Late-toxicity group: 32 of the 36 post-RT parotid fitted well with 3 Gaussian components, with mean intensities of 49.7±7.6, 77.2±8.7, and 118.6±11.8 (R-squared>0.98).

Conclusion:RT-associated parotid-gland injury is common in head-and-neck RT, but challenging to assess. This work has demonstrated that the Gaussian mixture model of the echo-histogram could quantify acute and late toxicity of the parotid glands. This study provides meaningful preliminary data from future observational and interventional clinical research.


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