Nasopharyngeal carcinoma volume measurements determined with computed tomography: Study of intraobserver and interobserver variability

Objective: To investigate the intraobserver and interobserver variability of computed tomography-based volume measurements of nasopharyngeal carcinoma. Design: Prospective study. Setting: Tertiary care centre. Methods: The primary turnout volume of 13 nasopharyngeal carcinomas was repeatedly measured by two trained observers independently in two different sessions, using the summation of area technique. Main Outcome Measures: Mean turnout volume and its standard deviation were calculated for each tumour. Statistical analysis was done with multivariate analysis, linear regression, and a two-way analysis of variance (ANOVA) random effects model. Results: The coefficient of variation was less than 20% in 11 volume measurements, but a large discrepancy between observers was noted in two tumours with involvement of the paranasal sinuses. A good linear correlation was found between mean turnout volume and its standard deviation: standard deviation = 0.26 volume - 2.48 (r = .80). When the two tumours with a large coefficient of variation were excluded, the two-way ANOVA random effects model revealed that both the interobserver (p = .83) and the intraobserver (p = .90) effect are not statistically significant; interobserver variability was the major component of total variability (71.0%). Conclusions: Total variability in the computed tomography-based measurement of nasopharyngeal carcinoma volume is small by having the measurements done by a trained observer, except in tumours with involvement of the paranasal sinuses.