The effect of parotid gland-sparing IMRT on salivary composition, flow rate and xerostomia measures

Abstract

Objectives

To describe parotid gland (PG) saliva organic and inorganic composition and flow rate changes, after curative intensity-modulated radiotherapy (IMRT) for head and neck cancer (HNC) and analyse the relationship between PG saliva analytes and xerostomia measures.

Methods and Materials

Twenty-six patients recruited to five prospective phase 2 or 3 trials which assessed toxicity and efficacy of IMRT by HNC subsite, provided longitudinal PG salivas. Salivary flow rate, subjective and objective xerostomia measures were prospectively collected and salivas tested for inorganic and organic analytes. Statistical comparisons of longitudinal analyte changes and analysis for a relationship between dichotomised xerostomia score and saliva analytes were performed.

Results

One-hundred and forty-two PG saliva samples from twenty-six patients were analysed. At 3-6 months after IMRT, stimulated and unstimulated salivas showed significantly decreased flow rate, total protein (TP) secretion rate, phosphate concentration and increased lactoferrin (LF) concentration. Stimulated salivas alone had elevated LF secretion rate and beta-2-microglobulin (B₂M) concentration with decreased Calcium (Ca²⁺) and Magnesium (Mg²⁺) concentrations and Ca²⁺ secretion rate. At >12 months, under stimulated and unstimulated conditions, increased LF concentration and decreased Mg²⁺ and phosphate concentration persisted and, in stimulated saliva, there was decreased potassium (K⁺) and Mg²⁺ concentration. Unstimulated TP secretion rate was lower in the presence of high grade xerostomia. Otherwise, no relationship between xerostomia grade and PG salivary flow rate, TP and Ca²⁺ secretion rate was found.

Conclusion

Fewer significant differences in PG saliva analytes >12 months after IMRT indicate good functional recovery. Residual xerostomia after IMRT will only be further reduced by addressing the sparing of subsites of the PG or other salivary gland tissues, in addition to the PG.

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