Reproducibility of contouring parotid gland using CT and MR images in radiotherapy for nasopharyngeal carcinoma / 国际肿瘤学杂志

ABSTRACT

Objective To investigate the reproducibility and consistency in contouring parotid gland volume based on computed tomography (CT) and magnetic resonance (MR) images in patients with nasopharyngeal carcinoma during radiotherapy.Methods Twenty-seven patients with nasopharyngeal cancer in Shandong Cancer Hospital from December 2012 to May 2013 were randomly enrolled and underwent intensified CT and MR imaging before radiotherapy.The parotid gland were contoured with unified standard on both CT and T1-MR images by 11 radiotherapists.Specifically,one radiotherapist sketched the parotid gland on CT and MR images for ten times as intra-group comparison,the other ten were asked to sketch the parotid gland on CT and MR images only once as inter-group comparison.The intra-and inter-group's variations of parotid gland volumes were analysed.Results The average volumes of intra-group on CT and MR images were (33.8 ±9.4) cm3(L),(33.2±7.6) cm3(R) and (24.4 ±7.6) cm3(L),(22.5 ±7.4) cm3(R).As well,for inter-group the average volumes were (34.6 ± 12.1) cm3 (L),(34.3 ± 9.0) cm3 (R) and (24.6 ± 7.6) cm3 (L),(23.2 ± 8.1) cm3(R),respectively.The volume variable ratios on CT images were (6.8 ± 1.5)％ (L),(6.3 ± 1.5) ％ (R) for intra-group and (18.0 ± 4.8) ％ (L),(17.4 ± 4.6) ％ (R) for inter-group.Similarly,the intra-and inter-group ratios for contouring on MR images reached (2.3 ±0.4)％ (L),(2.1 ±0.7)％ (R) and (4.7 ±0.7)％ (L),(5.0±0.6)％ (R),respectively.Conclusion Parotid gland contouring based on MR images has a better reproducibility and consistency than that based on CT images.It is beneficial to get a more objective and true indicator to estimate the radiation injury of parotid gland.