Early prediction of parotid glands secretory function based on ADC variations during radiotherapy for nasopharyngeal carcinoma: a phase II prospective study.

Objectives: This study aimed to quantify dynamic changes in the Apparent Diffusion Coefficient (ADC) values of the parotid glands during radiotherapy and explore their correlation with early-stage gland dysfunction.

Methods: Nasopharyngeal carcinoma patients receiving definitive chemoradiotherapy were prospectively enrolled. Magnetic Resonance Diffusion-Weighted Imaging (MR-DWI) was performed at pre-radiotherapy (pre-RT), the 5th, 15th fractions, and end of radiotherapy. ADC values and volumes for ipsilateral (IP) and contralateral parotid glands (CP) were recorded. Salivary function was assessed using scintigraphy (SGS) and the Radiation Therapy Oncology Group (RTOG) xerostomia criteria.

Results: A total of 80 eligible patients were analyzed. From pre-radiotherapy(pre-RT) to the end of radiotherapy, Pearson correlation analysis showed that changes in ADC values were positively correlated with the delivered dose (p < 0.01) and reduction in parotid volume (p < 0.01).From pre-RT to the 5th fraction, mean ADC values((ΔADC5) increased significantly by 17.7% (IP) and 16.3% (CP) (p < 0.01), with minimal volume changes(ΔrV5) (p = 0.060, p = 0.068). Spearman analysis revealed a positive association between the change in ΔADC5 and the incidence of xerostomia 6 months after radiotherapy (p < 0.01). Multivariable analysis identified ΔADC5 rather than ΔrV5 as an independent predictor of secretory dysfunction (IP: Odds Ratio (OR) = 1.010, p = 0.015 by SGS; OR = 1.026, p = 0.000 by RTOG; CP: OR = 1.017, p = 0.004 by SGS; OR = 1.015, p = 0.002 by RTOG).

Conclusion: This study analyze the dynamic changes in parotid gland ADC values, volume, and secretion function throughout radiotherapy. Changes in ΔADC5 can predict radiation-induced parotid gland injury before significant volume changes occur, thereby enabling early intervention.