Locoregional Recurrence of De-escalated Radiation Dose in Selected Nasopharyngeal Carcinoma: Experience from a Single Center Institution

Abstract

In the era of intensity modulated radiotherapy (IMRT), nasopharyngeal carcinoma (NPC), especially in stage T1-3, could achieve excellent locoregional control rate higher than 90% after definitive radiotherapy. The outstanding locoregional controlling may lead to dose de-escalation in highly selected patients. In order to assess the locoregional recurrence and long-term outcome of de-escalated dose in T1-3 NPCs treated with IMRT, a retrospective propensity score analysis was conducted. A total of 264 patients diagnosed with T1-3NanyM0 nasopharyngeal carcinoma between June 2011 and June 2015 were retrospective analyzed. With a median age of 50 years old, 66 patients were female and 198 were male. All the patients were treated with IMRT. The prescription IMRT dose, namely the standard dose, in our institution is 69.96Gy/2.12Gy/33F or 70Gy/2Gy/35F to primary tumor and cervical metastatic lymph nodes, 60.06Gy/1.82Gy/33F or 59.5Gy/1.7Gy/35F to high risk target and 50.96Gy/1.82Gy/28F or 51Gy/1.7Gy/30F to low risk target. About 74% of these patients were treated with induction chemotherapy, 67% were treated with concurrent chemotherapy. With a median follow-up time of 48 months. The 5-year locoregional failure free survival (LRFS), distant metastasis free survival (DMFS), disease free survival (DFS), and overall survival (OS) were 90.0%, 81.2%, 76.1% and 83.5%, respectively. Thirty patients received IMRT dose less than prescription dose, categorized as dose de-escalation group, with a median dose of 64Gy (60-68Gy). Of the 30 patients in dose de-escalation group, 24 were treated with induction chemotherapy and 21 were treated with concurrent chemotherapy. Other 234 patients received exactly prescription dose were categorized as standard dose group, with irradiation dose of 70Gy. Propensity scores were computed (30 patients for dose de-escalation group and 60 patients in standard dose group), and there is no significant difference in 5-year LRFS and 5 year OS between two groups (90.1% and 82.5% in standard dose group; 92.0% and 80.1% in dose de-escalation group, p=0.354 for LRFS and 0.879 for OS). No independent prognostic factor, including age, gender, T stage, N stage and RT dose, was associated with loco-regional failure in multivariate analysis. In our results, highly selected T1-3 nasopharyngeal carcinoma, especially those with response to induction chemotherapy, a moderate de-escalation dose delivered with IMRT are with comparable outcomes to those of standard dose.