Early radiation-induced changes evaluated by intravoxel incoherent motion in the major salivary glands.

Purpose: To investigate the potential of intravoxel incoherent motion (IVIM) MRI for early evaluation of irradiated major salivary glands.

Materials And Methods: Thirty-four patients with head-neck cancer were included in a prospective study. All patients underwent three serial IVIM-MRI: before, half-way through, and at the end of radiotherapy (RT). Apparent diffusion coefficient (ADC), ADClow derived in the low b-value range, perfusion fraction f, and pure diffusion coefficient D were estimated. Pretreatment values and early changes of diffusion parameters were correlated with parotid mean dose (Dmean ) and volume reduction after RT.

Results: Changes in diffusion parameters over time were all significant (P < 0.001 for ADC, ADClow , and D, P = 0.003 for f). Variations of ADC, ADClow , and f were not correlated with Dmean (P = 0.089, P = 0.252 and P = 0.884, respectively), whereas a significant relationship was found between changes in D and Dmean (r = 0.197 with CI95% = 0.004-0.375, P = 0.046). Pretreatment f and Dmean were the best independent predictors for the percentage shrinkage (P = 0.0003 and 0.0597 respectively; R(2) = 0.391).

Conclusion: Early changes of irradiated major salivary glands can be noninvasively evaluated by IVIM-MRI. Perfusion-related coefficients in conjunction with dosimetric information increase our capability to predict the change in parotid volume and hence, if further validated, guide treatment strategy in RT.