Magnetic Resonance Technologies To Evaluate Radiation-induced Xerostomia In Patients With Nasopharyngeal Carcinoma

Magnetic Resonance Technologies to Evaluate Radiation-induced Xerostomia in Patients with Nasopharyngeal Carcinoma[Purpose] To investigate the value of magnetic resonance sialography (MRS) and diffusion-weighted magnetic resonance imaging (DW MRI) as noninvasive tools to evaluate major salivary gland function before and after radiotherapy (RT) for nasopharyngeal carcinoma (NPC), and to investigate effects of induction chemotherapy on salivary function in these patients. [Materials and Methods]From August 2009 to March 2010, patients with nonmetastatic nasopharyngeal carcinoma were enrolled. stageⅠandⅡa (AJCC/UICC 2002) patients were treated with intensity modulated radiation therapy (IMRT) alone, and stageⅢandⅣpatients with additional induction and adjuvant chemotherapy. MRS and DW MRI with salivary stimulation were performed in patients before and after radiation therapy on a 3.0T MR scanner. An MRS categorical scoring system was used to compare the visibility of ducts pre-RT and post-RT. The EORTC Core QOL questionnaire and the EORTC Head and Neck QOL questionnaire were completed. Spearman rank correlation test was performed to analyze the nonstimulated and stimulated MRS findings and the clinical severity of xerostomia.[Results] 17 patients were enrolled (5 in RT alone group and 12 in sequential radiotherapy and chemotherapy group). All the patients completed planned treatment. The mean dose for the parotid glands was 39.04 Gy (SD,3.75Gy), and for the submandibular glands it was 57.83 Gy (SD,2.95Gy). Compared with patients in sequential treatment group, patients who received RT alone had statistically (P<0.05) significant improvements in the scale of nausea and vomiting in QLQ-C30 and in 9 xerostmia-related scales in QLQ-H&N35. Good-quality MR sialographic images were obtained. The visibility scores of both the parotid and submandibular ducts were increased after secretion stimulation. Irradiation produced insufficient visualization of the salivary ducts and attenuated the response to secretion stimulation. The postirradiation study revealed significant difference of secretion response of the parotid gland (rP) between RT alone group and sequential treatment group (P=0.023). Significant correlations were found between post-RT secretion rP and EORTC QLQ scales (global QOL scale in QLQ-C30[rs=0.485, p=0.049] and xerostomia scale in QLQ H&N35 [rs=-0.486, p=0.048]). Before RT, the mean ADC value of the parotid glands at rest was (1.16±0.18)×10-3mm2/s. During the first 5 min of stimulation, the ADC value showed an increase, and the mean peak ADC value was (1.27±0.18)×10-3mm2/s (P<0.001). The baseline ADC value at rest was significantly higher after RT than before RT but the stimulation response was lost after RT. For patients in the sequential treatment group, there was significant difference of rP between mean dose of parotid≤39Gy-group and> 39Gy-group (P=0.016). Significant difference was also observed between rP of V35≤median value-group and that of V35> median value-group (P=0.041).[Conclusions] MRS and DW MRI allow noninvasive evaluation of functional changes in the major salivary glands before and after RT and are promising approaches for investigating radiation-induced xerostomia. Early influence on xerostomia caused by sequential chemotherapy and radiotherapy is more serious than that caused by RT alone. It may contribute to the improvement of rP if the dose of irradiation to the parotid is reduced.