SU-E-J-111: The Contouring Error of the Parotids Based On the CT and MRI Images in Radiotherapy Planning for Nasopharyngeal Carcinoma




To analyze the variation of sketching the parotid for patients with nasopharyngeal carcinoma who underwent radiotherapy based on computed tomography (CT) and magnetic resonance(MR) images.


41 nasopharyngeal cancer patients were randomly selected. Each patient underwent MR and CT scanning. The Gross Tumor Volume and Organs at risk were contoured on both contrasted CT and T1-MR images. For each patient, one radiotherapist sketched the parotid on CT and MR images for 10 times, and 10 different radiotherapists were asked to sketching the parotid on CT and MR images only one time. The inter- and intra-observers volumes and outline variations were compared.


The volumes of parotid contoured by inter-observer on CT and MR images were 34.6±12.1cm3(left),34.3±9.0cm3(right) and 24.6±7.6cm3(L),23.2±8.1cm3(R); In the same way, for intra-observer on CT and MR images the volumes were 28.2±7.6cm3(L),29.4±9.4cm3(R) and 24.4±7.6cm3(L),22.5±7.4cm3(R), respectively. The variable ratios of volume on MR images were 4.7±0.7%(L),5.0±0.6%(R) for inter-observer and 2.3±0.4%(L),2.1±0.7%(R) for intra-observer. Similarly, The inter- and intra-observer ratios for contouring on CT images reached 18.0±4.8%(L),17.4±4.6%(R) and 6.3±1.5%(L),6.8±1.5%(R), respectively.


Contouring the parotids on MR images was more accurate and reproducible than that on CT images.