Correlation of CT simulator images with the dynamic MRI images in determining the position of gross tumor volume (GTV) in lung cancer radiotherapy (RT) planning

Objective: The aim of our study was comparison and correlation of CC tumor location in CTsimulator images with mean CC tumor location in Dynamic MRI (DMRI) as well as evaluation of the maximum amount of movements of the tumor in CC, ML and AP axes during the respiratory cycle using data obtained from DMRI.Method: In our study, image data of patients with lung cancer who had a 3DCRT plan using CT-simulator and who also had DMRI were used. Amount of maximum tumor movement (CC_MR, ML_MR, AP_MR) due to inspiration and expiration was measured in three axes in DMRI images. In CT-simulator images, CC distance of GTV upper limit to the reference line (CC_BT) was measured. In DMRI images the same distance was identified in inspiration (CCins_MR) and expiration (CCexp_MR) and the average value (CCort_MR) was found. The values of CCort_MR and CC_BT were compared using Wilcoxon signed-rank test and were evaluated with Spearman correlation test.Results: The comparison revealed no statistically significant difference between CTsimulator and DMRI (p= 0,172). In addition, a correlation between the two surveys was observed (p<0,0001).Conclusion: In our study, the maximum value of CCins_MR - CCort_MR was found 0,4 cm and this data supports the relevance of PTV margin of 1 cm in our department. The tumor location in CT-simulator correlates well with the one in DMRI. However, DMRI can be used in the radiotherapy planning of especially small size, peripheric and lower lobe tumors.Key Words: GTV, CT-simulator, Dynamic MRI, respiratory