DWI-ADC For Early Prediction And Dynamic Detection Of Parotid Gland Secretion In Patients With Head And Neck Cancer During Radiotherapy:a Prospective Clinical Study

bjective:To study the dynamic changes of ADC value of bilateral parotid gland in patients with head and neck cancer during adaptive radiation therapy(ART), and to explore the correlation between the changes of ADC value and the radiation dose, volume withdrawal and the function of gland secretion, provide a new method to evaluate the function of salivary gland in the early stage, and to guide the clinical protection of the parotid gland. Methods: 60 head and neck cancer patients treated with intensity modulated radiotherapy were enrolled in this prospective study from Jun. 2015 to Oct. 2015. The salivary gland cancer patients were not included. DWI investigations were performed on 3.0T MRI(b=0,500,800s/mm2) at pre-radiation, the 15 th radiation, the 25 th radiation and post-radiation. ADC values were measured in the largest cross section of deep and superficial lobes for parotid glands respectively(deep lobe of ipsilateral: P1; superficial lobe of ipsilateral: P2; deep lobe of contralateral: P3; superficial lobe of contralateral: P4). Chewing stimulates test, radionuclide scan and RTOG criteria were used to evaluate the secret function weekly. Pearson analysis was used to assess the correlation between ADC, delivered radiation dose, volume regression, and secret function of parotid glands during the course of radiotherapy.Results: All the patients exhibited mean ADC increase in parotid glands, with mean increased ratios of 0.37±0.15(P1),0.35±0.13(P2),0.35±0.17(P3) and0.35±0.09(P4) between pre-and post-radiation. ADC changes in spinal cord were almost invisible(ratio?0.04±0.01).Chewing stimulates test, radionuclide scan and RTOG criteria showed decreasesd secretion function in all patients at post-radiation. The increased mean ADC had a statistical positive correlation with the increased delivered dose(r1=0.98; r2=0.96; r3=0.964; r4=0.947), and had a significantly negative correlation with the volume reduction(r1=-0.61; r2=-0.54; r3=-0.51; r4=-0.48) and secret function of parotid glands(r1=-0.74; r2=-0.71; r3=-0.69; r4=-0.68). The mean ADC of deep lobe of ipsilateral parotid gland had greatest change among the other lobes. Furthermore, the mean ADC changed early at 15 th fraction(ratio: 0.48±0.15), while the volume and secret function of parotid gland had no significant change at 15 th fraction(ratio: 0.08±0.05, 0.09±0.03). During the course of radiotherapy, the increased mean ADC had the strongest relation with the delivered dose at 15 th radiation(r=0.83). The higher the mean ADC at 15 th radiation, the lower the secret function at post-radiation(r=-0.76).Conclusion:ADC value of parotid glands increased greatly for head and neck cancer patients during the course of radiotherapy. It had a close negative correlation with the volume reduction and secret function, and a close positive correlation with the increased delivered dose of parotid glands. Deep lobe of ipsilateral parotid glands was the most sensitive anatomic area for radiation. Dynamic ADC change might be a new and early indicator to predict and evaluate the secret function of parotid glands.