Comparison of Fused MRI/CT-Based Contouring and CT-Based Contouring in Helical Tomotherapy for Rectal Cancer

Due to the limitations of CT imaging, it is necessary to use magnetic resonance imaging (MRI) as a complementary method in the treatment planning process. This study aimed to compare contouring and treatment planning based on MRI/CT images with contouring and treatment planning based on CT images in the treatment of rectal cancer using helical tomotherapy.

In this prospective study, 12 patients with rectal cancer underwent MRI diagnostic imaging and CT imaging was also performed at an interval of one day. The contouring process was performed for each patient based on both methods. After that, a dose of 45 Gy was delivered to the planning target volume (PTV). Finally, the size of the treatment volumes and the parameters Dmean, V45, HI, CI, and D98% were extracted and compared from the treatment planning system.

CT-based contouring method compared to MRI/CT-based method showed higher averages for treatment volumes. In addition, in CT-based plans compared to MRI/CT-based plans, the average CI, V45, and D98% were significantly lower and the average HI was significantly higher.

The results of this study show that contouring based on MRI/CT images can estimate the size of treatment volumes smaller than contouring based on CT. Also, treatment plans based on MRI/CT images can provide more appropriate dose coverage for PTV.