The Influence Of The Longest Continuous Radiotherapy Interruption Time On The Survival Of Newly Treated Non-distant Metastatic Nasopharyngeal Carcinoma

Objective:To explore and analyze the impact of the longest continuous radiotherapy interruption time(CIT)on the survival of nasopharyngeal carcinoma,to provide reference for clinical treatment.Materials and methods:A total of 646 patients with stage I-IVA NPC were treated in the affiliated Cancer Hospital of Guangxi Medical University from January 2013 to December 2014,IMRT is used in all patients.The effect of the longest interruption of continuous radiotherapy on the prognosis of nasopharyngeal carcinoma was analyzed.Each patient was followed up for at least 5 years or until the final event(death)or loss of follow-up.The survival curve was drawn by Kaplan-Meier method and the survival rate after metastasis was calculated by Log-rank method.Cox proportional hazard regression model was used for multi-factor analysis.The main end point was 5-year overall survival(OS),followed by progression-free survival(PFS),local regional recurrence-free survival(LRFS)and distantfailure-free survival(DFFS).Results:The longest continuous interruption time of radiotherapy was 4,5,6 and 7 days respectively.There was no significant difference in OS,PFS,LRFS,DFFS,survival analysis,univariate analysis and multivariate analysis.Survival analysis showed that CIT≥4 days and CIT<4 days 5 years OS(80.2% and79.8%),P= 0.89),CIT ≥ 5 days and CIT < 5 days 5 years OS(79.4% and 80.4%P= 0.75),CIT ≥ 6 days and CIT < 6 days 5 years OS(79.2% and 80.2%P=0.83),CIT ≥ 7 days and CIT < 7 days 5 years OS(80.4% and 79.9%P=0.92).Multivariate analysis showed that CIT≥4 days and CIT <4 days 5 years OS(HR 1.02,95%CI 0.7-1.49;P=0.93),CIT ≥ 5 days and CIT < 5 days 5 years OS(HR 1.2,95%CI、0.8-1.78;P=0.38),CIT ≥ 6 days and CIT < 6 days OS(HR1.27 95% CI,0.78-2.07.0.34),CIT ≥ 7 days and CIT < 7 days 5 years OS(HR1.52 95% CI,0.67-3.45 P= 0.31).Stratified analysis showed that compared with CIT ≥ 7 days and CIT < 7 days,only CCRT group had an increased risk of recurrence(HR 3.16(1.10,9.05)P = 0.03);Compared with the interruption of continuous radiotherapy time ≥ 6 days and < 6 days,the risk of death increased in the younger age group after the third age group(HR 3.12(1.16,8.34)P =0.02).Conclusion: In the era of IMRT,when the longest continuous radiotherapy interruption time was 7 days or less,there was no significant effect on OS,PFS,LRFS and DFFS of 5 years in patients with I-IVA stage nasopharyngeal carcinoma,but when the longest continuous radiotherapy interruption time ≥ 7days,only CCRT alone,we need further study to evaluate whether the risk of recurrence is increased;When the longest continuous radiotherapy interruption time is ≥ 6 days,we need further research in the younger age group to assess whether the risk of death is increased.