Evaluation of salivary gland function after treatment of head-and-neck tumors with intensity-modulated radiotherapy by quantitative pertechnetate scintigraphy

Abstract

Purpose To evaluate salivary gland function after inversely planned stereotactic intensity-modulated radiotherapy (IMRT) for tumors of the head-and-neck region using quantitative pertechnetate scintigraphy. Methods and materials Since January 2000, 18 patients undergoing IMRT for cancer of the head and neck underwent pre- and posttherapeutic scintigraphy to examine salivary gland function. The mean dose to the primary planning target volume was 61.5 Gy (range 50.4–73.2), and the median follow-up was 23 months. In all cases, the parotid glands were directly adjacent to the planning target volume. The treatment planning goal was for at least one parotid gland to receive a mean dose of <26 Gy. Two quantitative parameters (change in maximal uptake and change in the relative excretion rate before and after IMRT) characterizing the change in salivary gland function after radiotherapy were determined. These parameters were compared with respect to the dose thresholds of 26 and 30 Gy for the mean dose. In addition, dose–response curves were calculated. Results Using IMRT, it was possible in 16 patients to reduce the dose for at least one parotid gland to ≤26 Gy. In 7 patients, protection of both parotid glands was possible. No recurrent disease adjacent to the protected parotid glands was observed. Using the Radiation Therapy Oncology Group/European Organization for the Research and Treatment of Cancer scoring system, only 3 patients had Grade 2 xerostomia. No greater toxicity was seen for the salivary glands. The change in the relative excretion rate was significantly greater, if the parotid glands received a mean dose of ≥26 Gy or ≥30 Gy. For the change in maximal uptake, a statistically significant difference was seen only for the parotid glands and a dose threshold of 30 Gy. For the end point of a reduction in the parotid excretion rate of >50% and 75%, the dose–response curves yielded a dose at 50% complication probability of 34.8 ± 3.6 and 40.8 ± 5.3 Gy, respectively. Conclusion Using IMRT, it is possible to protect the parotid glands and reduce the incidence and severity of xerostomia in patients. Doses <26–30 Gy significantly preserve salivary gland function. The results support the hypothesis that application of IMRT does not lead to increased local failure rates.