Early changes of parotid density and volume predict modifications at the end of therapy and intensity of acute xerostomia

Purpose. To quantitatively assess the predictive power of early variations of parotid gland volume and density on final changes at the end of therapy and, possibly, on acute xerostomia during IMRT for head-neck cancer. Materials and methods. Data of 92 parotids (46 patients) were available. Kinetics of the changes during treatment were described by the daily rate of density (r Delta rho) and volume (r Delta vol) variation based on weekly diagnostic kVCT images. Correlation between early and final changes was investigated as well as the correlation with prospective toxicity data (CT-CAEv3.0) collected weekly during treatment for 24/46 patients. Results. A higher r Delta rho was observed during the first compared to last week of treatment (-0,50 vs -0,05 HU, p-value = 0.0001). Based on early variations, a good estimation of the final changes may be obtained (Delta rho: AUC = 0.82, p = 0.0001; Delta vol: AUC = 0.77, p = 0.0001). Both early r Delta rho and r Delta vol predict a higher "mean" acute xerostomia score (>= median value, 1.57; p-value = 0.01). Median early density rate changes for patients with mean xerostomia score >=/< 1.57 were -0.98 vs -0.22 HU/day respectively (p = 0.05). Conclusions. Early density and volume variations accurately predict final changes of parotid glands. A higher longitudinally assessed score of acute xerostomia is well predicted by higher r Delta rho and r Delta vol in the first two weeks of treatment: best cut-off values were -0.50 HU/day and -380 mm(3)/day for r Delta rho and r Delta vol respectively. Further studies are necessary to definitively assess the potential of early density/volume changes in identifying more sensitive patients at higher risk of experiencing xerostomia.