Analysis of Salivary Flow and Dose–Volume Modeling of Complication Incidence in Patients With Head-and-Neck Cancer Receiving Intensity-Modulated Radiotherapy

Purpose

To investigate dose–volume effects of salivary flow and the functional recovery over time, using salivary function data and different models of normal tissue complication probability (NTCP).

Methods and Materials

A total of 59 patients with head-and-neck cancer treated with intensity-modulated radiotherapy (IMRT) were analyzed in the present study. The toxicity was evaluated using the Radiation Therapy Oncology Group (RTOG) scale and salivary flows, both unstimulated (USF) and stimulated (SSF). The assessments were done before radiotherapy (RT) and at 3, 6, 12, 18, and 24 months after RT. Grade 3 toxicity was the primary endpoint. Analyses of toxicity incidence at 3, 6, and 12 months after RT were performed by both the Lyman-Kutcher-Burman (LKB) and relative seriality (S) models.

Results

A significant correlation was found between the incidence of Grade 3 toxicity and the incidence of patients with a reduction in SSF to <25% of the pre-RT value. Better correlations resulted between the RTOG toxicity score and the dosimetric parameters, compared with USF/SSF. The TD₅₀, assessed by the LKB model, was 21.4, 27.8, and 41.6 Gy at 3, 6, and 12 months after RT, respectively. The TD₅₀, assessed by the S model, was 20.0, 26.3, and 40.0 Gy at 3, 6, and 12 months after RT, respectively.

Conclusion

Recovery of salivary gland function vs. time after RT took place mostly within 1 year after RT. The RTOG Grade 3 was a reliable score to perform the NTCP modeling. The choice of NTCP model had no influence on the accuracy of predictions.

Xerostomia, Salivary function, Dose–volume effects, Normal tissue complication probability, IMRT