Impact on xerostomia for patients with nasopharyngeal carcinoma treated with superficial parotid lobe-sparing intensity-modulated radiation therapy (SPLS-IMRT): A prospective phase II randomized controlled study.

Abstract

6059 Background: In the intensity-modulated radiation therapy (IMRT) era, xerostomia remains one of the most common radiation-induced toxicities in nasopharyngeal carcinoma (NPC) patients. We first proposed the superficial parotid lobe–sparing IMRT (SPLS-IMRT) technique in NPC, which has been proved to significantly reduce the mean doses of bilateral entire parotid glands and superficial parotid lobes. To further validate its clinical benefits, we conducted a prospective phase II randomized controlled study to compare the incidence of xerostomia in NPC patients treated with SPLS-IMRT and conventional IMRT (C-IMRT). Methods: Patients with histologically confirmed NPC who met the eligibility criteria were randomly assigned in a 1:1 ratio to receive either SPLS-IMRT or C-IMRT. The V36 (the percentage volume receiving a dose of 36 Gy) of the entire parotid gland was constrained to be less than 40% in both groups. Additionally, V26 (the percentage volume receiving a dose of 26 Gy) of the superficial parotid lobe was constrained to be less than 30% in the SPLS-IMRT group. The primary endpoint was the incidence of xerostomia at 12 months post-IMRT. The secondary endpoints included the xerostomia questionnaire (XQ) score, unstimulated salivary flow rate (USFR), stimulated salivary flow rate (SSFR), and survival outcomes. Results: From January 2018 to September 2018, 90 patients were enrolled (45 per group). Eighty-two patients were included for xerostomia analysis (42 in the SPLS-IMRT group and 40 in the C-IMRT group). At 12 months post-IMRT, the incidence of xerostomia in the SPLS-IMRT group was significantly lower than that in the C-IMRT group (83.4% vs. 95.0%; P = 0.007), especially the grade 3 xerostomia (0% vs. 12.5%; P < 0.001). However, the median change in XQ score (XQchange) was similar between the two groups (11.9 points vs. 14.1 points; P = 0.194). Moreover, there was a significantly higher median fractional USFR (0.67 vs. 0.35; P = 0.024) and SSFR (0.66 vs. 0.32; P = 0.021) in the SPLS-IMRT group than the C-IMRT group. All 90 patients were included for survival analysis. With a median follow-up time of 37.8 months (IQR, 33.9–38.5 months), the 3-year locoregional relapse-free survival, distant metastasis-free survival, and overall survival in the SPLS-IMRT and C-IMRT groups were 92.5% vs. 90.9% (hazard ratio [HR], 1.84; P = 0.477), 83.8% vs. 81.7% (HR, 1.13; P = 0.816), and 88.9% vs. 88.2% (HR, 0.96; P = 0.949), respectively. Conclusions: SPLS-IMRT significantly reduced the incidence of xerostomia at 12 months post-IMRT in NPC by recovering parotid gland function earlier than C-IMRT, without compromising survivals. Phase III clinical trials are needed to confirm this result. Clinical trial information: NCT05020067.