Scintigraphy in prediction of the salivary gland function after gland-sparing intensity modulated radiation therapy for head and neck cancer

Background and purpose: To evaluate salivary gland scintigraphy in prediction of salivary flow following radiation therapy. Patients and methods: Twenty patients diagnosed with head and neck cancer were treated with intensity modulated radiation therapy with an intention to spare the salivary gland function. The total quantitative saliva secretion was measured prior to and 6 and 12 months after therapy, and the function of the major salivary glands was monitored using Tc-99m-pertechnetate scintigraphy. Two models were designed for prediction of the post-treatment salivary flow: an average model, based on the average proportions of saliva produced by each of the four major glands in healthy subjects, and an individual model, based on saliva produced by each gland as measured by scintigraphy prior to therapy. These models were compared with volume-based (Lyman) normal tissue complication probability models using two published sets of model parameters. Results: The D50 for the parotid and the submandibular gland function assessed at 6 and 12 months after radiotherapy was approximately 39 Gy. The scintigraphy-based individual model predicted well the measured post-treatment saliva flow rates. The correlation coefficient between the predicted stimulated and the measured saliva flow rate was 0.77 (p < 0.0001) at 6 months and 0.55 (p = 0.034) at 12 months after completion of radiotherapy. The relative changes in unstimulated and stimulated salivary flow rates showed similar dependency on the cumulative radiation dose. Conclusions: Salivary gland function assessed by scintigraphy prior to radiotherapy is useful in prediction of the residual salivary flow after radiotherapy