Reduced-dose radiotherapy for Epstein-Barr virus DNA selected staged III nasopharyngeal carcinoma: A single-arm, phase 2 trial

Background Radiotherapy-related toxicities of nasopharyngeal carcinoma (NPC) caused by a standard dose of 70 Gy remain a critical issue. Therefore, we assessed whether a radiotherapy dose of 60 Gy was non-inferior to the standard dose in patients with low-risk stage III NPC with a favourable response to induction chemotherapy (IC). Patients and methods We did a single-arm, single-centre, phase II clinical trial in China. Patients with low-risk (Epstein-Barr virus [EBV] DNA level <4000 copies/ml) stage III NPC were treated with two cycles IC. Patients with complete/partial response and undetectable EBV DNA level were assigned 60 Gy intensity-modulated radiotherapy concurrently with three cycles of cisplatin. The primary end-point was 2-year progression-free survival (PFS). This trial is registered with ClinicalTrials.gov, number NCT 03668730. Results One patient quit because of withdrawal of informed consent after IC. In total, 215 patients completed two cycles of IC, after which 116 (54.0%) and 99 (46.0%) patients were assigned 60 and 70 Gy radiotherapy, respectively. For 215 patients, the 2-year PFS was 90.7% (95% CI, 86.8%–94.6%) with a median follow-up of 43.9 months (interquartile range [IQR], 39.8–46.2). For patients treated with 60 Gy radiotherapy, the 2-year PFS rate was 94.8% (95%CI 90.7%–98.9%) with a median follow-up of 43.9 months (IQR 40.2–46.2). The most common late toxicity was grade 1–2 dry mouth (incidence rate: 54.3%). No grade 3+ long-term adverse event was observed, and most quality-of-life items, domains, and symptom scores returned to baseline by 6 months. Conclusion Reduced-dose radiation (60 Gy) is associated with favourable survival outcomes and limited treatment-related toxicities in patients with low-risk stage III NPC sensitive to IC.