This is a multi-center, non-inferiority, open-label, randomized controlled phase III clinical trial in primary diagnosed nasopharyngeal carcinoma (NPC) patients without distant metastasis. This study aims to compare the regional control, survival outcomes, radiation-related toxicities, and quality of life (QoL) of xerostomia-optimized intensity-modulated radiotherapy versus standard intensity-modulated radiotherapy in NPC patients

Xerostomia remains one of the most common radiation-induced toxicities, and approximately 80% to 90% of NPC patients still experience varying degrees of xerostomia post-IMRT. Among the major salivary glands, the parotid gland is the largest and produces 60% to 65% of the oral saliva output. Studies have revealed that xerostomia post-IMRT is mainly dependent on the irradiation dose of the parotid glands. Clinical target volumes (CTV) for the cervical nodal region starting from skull base have been the standard in nasopharyngeal carcinoma for several decades. Consequently, the parotid glands overlap with the target volumes and irradiation dose reaches 31.7 Gy to 43.9 Gy in most reports. Retrospective studies reveal that the lateral process of C1 is a suitable cranial edge for neck CTV delineation; therefore, the volume of the parotid glands exposed to high radiation doses can be greatly reduced. we conducted this trial comparing outcomes ,toxicities and QoL of xerostomia-optimized intensity-modulated radiotherapy versus standard intensity-modulated radiotherapy in nasopharyngeal carcinoma.

Inclusion Criteria:

• Newly histologic diagnosis of nasopharyngeal non-keratinizing carcinoma (WHO II/III);
• All genders, range from 18-70 years old;
• ECOG score 0-1;
• Clinical stage I-IVa (AJCC/UICC 8th);
• Not received radiotherapy, chemotherapy and other anti-tumor treatment (including immunotherapy);
• No contraindications to chemotherapy or radiotherapy;
• Adequate organ function: white blood cell count ≥ 4×109/L, neutrophile granulocyte count ≥ 1.5×109/L, hemoglobin ≥ 90g/L, platelet count ≥ 100×109/L; alanine aminotransferase or aspartate aminotransferase < 2.5×upper limit of normal; blood urea nitrogen or creatinine ≤ 1.5×upper limit of normal or endogenous creatinine clearance ≥ 60ml/min (Cockcroft-Gault formula);
• Sign the consent form.

Exclusion Criteria:

• Level II involvement with extracapsular extension (ECE), and/or had a maximum nodal axial diameter (MAD) of greater than 3cm in level II ;

  -≥4 nodal regions of ipsilateral neck involvement;

• Radiologically suspicious or confirmed involvement in level II area between skull base and the lateral process of C1;

• Parotid lymph node and/or parotid gland involvement;

• History of parotid disease or surgery;

• Previous malignancy or other concomitant malignant disease;

• Pregnancy or lactation.