Apparent diffusion coefficient histogram analysis can evaluate radiation-induced parotid damage and predict late xerostomia degree in nasopharyngeal carcinoma

// Nan Zhou 1, * , Tingting Guo 2, * , Huanhuan Zheng 1 , Xia Pan 1 , Chen Chu 1 , Xin Dou 1 , Ming Li 1 , Song Liu 1 , Lijing Zhu 3 , Baorui Liu 3 , Weibo Chen 4 , Jian He 1 , Jing Yan 3 , Zhengyang Zhou 1 and Xiaofeng Yang 5 1 Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008, China 2 Department of Radiology, Nanjing Drum Tower Hospital, Clinical College of Traditional Chinese and Western Medicine, Nanjing University of Chinese Medicine, Nanjing 210008, China 3 The Comprehensive Cancer Centre of Nanjing Drum Tower Hospital, Clinical College of Nanjing Medical University, Nanjing 210008, China 4 Philips Healthcare, Shanghai 200233, China 5 Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, Georgia 30322, USA * These authors have contributed equally to this work Correspondence to: Zhengyang Zhou, email: zyzhou@nju.edu.cn Jian He, email: hjxueren@126.com Jing Yan email: yj20030610@126.com Keywords: apparent diffusion coefficient, histogram analysis, radiotherapy, parotid glands, nasopharyngeal carcinoma Received: March 23, 2017      Accepted: June 27, 2017      Published: July 26, 2017 ABSTRACT We investigated apparent diffusion coefficient (ADC) histogram analysis to evaluate radiation-induced parotid damage and predict xerostomia degrees in nasopharyngeal carcinoma (NPC) patients receiving radiotherapy. The imaging of bilateral parotid glands in NPC patients was conducted 2 weeks before radiotherapy (time point 1), one month after radiotherapy (time point 2), and four months after radiotherapy (time point 3). From time point 1 to 2, parotid volume, skewness, and kurtosis decreased ( P < 0.001, = 0.001, and < 0.001, respectively), but all other ADC histogram parameters increased (all P < 0.001, except P = 0.006 for standard deviation [SD]). From time point 2 to 3, parotid volume continued to decrease ( P = 0.022), and SD, 75 th and 90 th percentiles continued to increase ( P = 0.024, 0.010, and 0.006, respectively). Early change rates of parotid ADC mean , ADC min , kurtosis, and 25 th , 50 th , 75 th , 90 th percentiles (from time point 1 to 2) correlated with late parotid atrophy rate (from time point 1 to 3) (all P < 0.05). Multiple linear regression analysis revealed correlations among parotid volume, time point, and ADC histogram parameters. Early mean change rates for bilateral parotid SD and ADC max could predict late xerostomia degrees at seven months after radiotherapy (three months after time point 3) with AUC of 0.781 and 0.818 ( P = 0.014, 0.005, respectively). ADC histogram parameters were reproducible (intraclass correlation coefficient, 0.830 - 0.999). ADC histogram analysis could be used to evaluate radiation-induced parotid damage noninvasively, and predict late xerostomia degrees of NPC patients treated with radiotherapy.