Interobserver variations in the delineation of planning target volume and with orgagans at risk different contouring methods in intensity-modulated radiation therapy for nasopharyngeal carcinoma

Abstract

Objective To assess the interobserver variations in delineating the planning target volume (PTV) and organs at risk (OAR) using different contouring methods during intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC), aiming to provide references for the quality control of multi-center clinical trials. Methods The PTV and OAR of CT image of 1 NPC patient manually delineated by 10 physicians from 8 different radiation centers were defined as the manual contour , and the OAR auto-contoured using the ABAS software and modified by the physicians were defined as the auto+ manual contour . The maximum/minimum ratio (MMR) of the PTV and OAR volumes, and the coefficient of variation (CV) for different delineated contours were comparatively evaluated. Results Large variation was observed in the PTV and OAR volumes in the manual contour group. The MMR and CV of the PTV were 1.72-3.41 and 0.16-0.39, with the most significant variation in the PTVnd (MMR=3.41 and CV=0.39 for the PTVnd-L). The MMR and CV of the manually contoured OAR were 1.30-7.89 and 0.07-0.67. The MMR of the temporal lobe, spinal cord, temporomandibular joint, optic nerve and pituitary gland exceeded 2.0. Compared with the manual contour group, the average contouring time in the auto+ manual group was shortened by 68% and the interobserver variation of the OAR volume was reduced with an MMR of 1.04-2.44 and CV of 0.01-0.37. Conclusions Large variation may occur in the PTV and OAR contours during IMRT plans for NPC delineated by different clinicians from multiple medical centers. Auto-contouring+ manually modification can reduce the interobserver variation of OAR delineation, whereas the variation in the delineation of small organs remains above 1.5 times. The consistency of the PTV and OAR delineation and the possible impact upon clinical outcomes should be reviewed and evaluated in multi-center clinical trials. Key words: Interobserver variation in delineation; Planning target volume; Organ at risk; Nasopharyngeal neoplasm/intensity-modulated radiation therapy