Differences in delineation of organs at risk lead to dose uncertainties during intensity-modulated radiotherapy for nasopharynx carcinoma

Objective: To assess the differences in delineation of organs at risk (OAR) and dosimetry between junior and senior physicians during intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC) and to evaluate the role of specific training in reducing the differences. Methods: Sixteen patients newly diagnosed with NPC were selected in the study. The OAR was delineated separately by three junior physicians and three senior physicians, and the geometric and dosimetric differences were assessed relative to the reference OAR. Delineation was performed again for the two OARs with the biggest difference after specific training in the two groups of physicians, and the differences were evaluated again. The difference was determined by paired t test. Results: The maximum dose differences (D_max) of OAR in the junior and senior physicians were (2.33 ± 12.06)% (-48.06%-137.82%) and (0.09 ± 4.72)% (-49.54%-42.96%), respectively (P = 0.039), and the difference in the optic chiasm was the greatest ((5.85 ± 19.63)%: (1.36 ± 4.64)%, P = 0.042). The mean dose differences (D_max) of OAR in the junior and senior physicians were (3.10 ± 8.07)% (-46.76%-59.76%) and (-0.93 ± 2.03)% (-45.54%-35.69%), respectively (P = 0.021), and the difference in the parotid gland was the greatest ((13.23 ± 13.39)%: (3.20 ± 6.71)%, P = 0.002). In the secondary delineation after training, the D_max of the optic chiasm in the junior and senior physicians was (1.68 ± 3.34)% and (1.50 ± 1.87)%, respectively (P = 0.841), and the difference in junior physicians was reduced significantly compared with before training ((1.68 ± 3.34)%: (5.85 ± 19.63)%, P = 0.048); the D_max of the parotid gland in the junior and senior physicians was (2.46 ± 3.06)% and (1.35 ± 3.00)%, respectively (P = 0.274), significantly reduced compared with before training ((2.46± 3.06)%: (13.23 ± 13.39)%, P = 0.002; (1.35 ± 3.00)%: (3.20 ± 6.71)%, P = 0.033). Conclusions: The differences in delineation of OAR lead to dose uncertainties during IMRT for NPC, and specific training can improve the accuracy of delineation. (authors)