Quantitative analysis of normal tissue effects in the clinic (QUANTEC) guideline validation using quality of life questionnaire datasets for parotid gland constraints to avoid causing xerostomia during head-and-neck radiotherapy

Purpose: To perform a validation test of the quantitative analysis of normal tissue effects in the clinic (QUANTEC) guidelines against quality of life (QoL) questionnaire datasets collected prospectively from patients with head and neck (HN) cancers, including HN squamous cell carcinoma (HNSCC) and nasopharyngeal carcinoma (NPC). Methods and materials: QoL questionnaire datasets from 95 patients with NPC and 142 with HNSCC were analyzed separately. The European Organization for Research and Treatment of Cancer H and N35 QoL questionnaire was used as the endpoint evaluation. The primary endpoint (grade 3+ xerostomia) was defined as moderate to severe xerostomia 3 and 12 months after the completion of RT, and excluded patients with grade 3+ xerostomia at the baseline. The Lyman–Kutcher–Burman normal tissue complication probability (NTCP) model was used to describe the incidence of xerostomia. Negative predictive values (NPVs) were used to determine the rate of correctly predicting the lack of complications. Results: NTCP fitted parameters were TD50 = 37.8 Gy (CI: 29.1–46.9 Gy), m = 0.59 (CI: 0.48–0.80) and TD50 = 43.9 Gy (CI: 33.2–52.8 Gy), m = 0.48 (CI: 0.37–0.76) at the 3-month and 12-month time points, respectively. For QUANTEC validation, HN and HNSCC data validation gave similar results at 3 months; at mean doses to the spared parotid of ⩽20 and ⩽25 Gy, the QoL dataset showed approximately 22% and 28% rates of xerostomia, respectively. At 12 months, the rates of xerostomia were approximately 13% and 19%, respectively. For NPC cases, the dataset showed approximately 0% and 33% (∼67% NPV) rates of xerostomia at 3 months. At 12 months, both rates of xerostomia were approximately 0% (∼100% NPV), which differed significantly from the results for the HNSCC cohort. Conclusion: The QoL datasets validated the QUANTEC guidelines and suggested that the modified QUANTEC 20/20-Gy spared-gland guideline is suitable for clinical use in HNSCC cohorts to effectively avoid xerostomia, and the QUANTEC 25-Gy guideline is justified for NPC cohorts