Assessing parotid gland function through diffusion weighted MRI during and post-radiotherapy in head and neck cancer patients

The purpose of this study was to evaluate the usefulness of apparent diffusion coefficient (ADC) variation in irradiated parotid glands during and after 3D conformal radiotherapy (3DCRT). This study enrolled 15 head and neck cancer (HNC) patients who were treated with 3DCRT underwent diffusion weighted imaging (DWI) at rest and after gustatory stimulation in three time points as follows: before, during (one day after receiving the mean dose 26 Gy) and 6 months after the end of radiotherapy (RT). Salivary Ejection Fraction (SEF) data was also obtained from salivary gland scintigraphy (SGS) at the same three time points as MRI. Mean ADC at rest and after stimulation (ADCr, ADCs) and SEF were extracted from parotid region for three time points. Finally, SEF and changes of ADC over time at rest and after stimulation and in each time point were compared. Difference between mean ADCr before RT and during RT was not significant (p = 0.12). The ADCr values were significantly higher after RT than before RT (p = 0.003) and during RT (after dose 26 Gy) (p = 0.001). The difference between ADCr and ADCs in each time point showed that there is significant difference between ADCr and ADCs before RT (p = 0.005). Difference between these parameters after RT was also significant (p = 0.05). Non-significant difference (p = 0.21) between ADCr and ADCs during RT was observed. The result of SEF also was significantly lower after RT than during (p = 0.008) and before RT (p = 0.001). Mean ADC values could be used as a surrogate marker to characterize the parotid function in different stages of RT.