High case volume of radiation oncologists is associated with better survival of nasopharyngeal carcinoma patients treated with radiotherapy: a multifactorial cohort analysis

Objectives: The relationship between physician case volume and patient outcome in patients with head and neck cancers such as nasopharyngeal carcinoma treated by radiotherapy is unknown. This study was designed to investigate the association between the case volume of radiation oncologists and the survival of patients with nasopharyngeal carcinoma. Design: Retrospective cohort study. Setting: Based on nationwide claims data (National Health Research Insurance Database) in the years 2002-2008. Participants: Newly diagnosed patients with nasopharyngeal carcinoma receiving curative radiotherapy in the year 2003. Main outcome measures: Overall survival until 2008. We used the running log-rank test to decide the optimal threshold for categorising the case volume of radiation oncologists. The characteristics of patients, their treatments and contact with health service providers were considered as co-explanatory variables. The log-rank test and Cox regression were performed. Sensitivity analyses were carried out regarding major study assumptions. Results: Five hundred and sixty-two patients with nasopharyngeal carcinoma newly diagnosed in 2003 were identified as the study cohort. The 5-year overall survival was better among patients treated by high-volume (6 patients in year 2002) radiation oncologists than by low-volume (<6 patients in year 2002) radiation oncologists (77% versus 64%, P = 0.0007). The adjusted hazard ratio of death was 0.65 (95% confidence interval, 0.48-0.91) upon multivariate analysis. Patients aged at least 65 years also had a lower survival rate than those younger than 65 years old (adjusted hazard ratio of death: 2.81, 95% confidence interval: 1.94-4.08). The physician case volume and patient outcome effect remained the same after sensitivity analyses. Conclusions: Patients with nasopharyngeal carcinoma treated by high-volume radiation oncologists have better survival compared with those treated by low-volume radiation oncologists. Further studies are needed to verify our findings with similar cancer cohorts treated by modern radiotherapy techniques or other types of radiotherapy.