To Assess the Changes of Volume and Spatial Location of Target Area During Cone Beam Computed Tomography for Cervical Cancer

Abstract

To assess the changes in volume and spatial location of target area and surrounding organs during cone beam computed tomography (CBCT) for cervical cancer. Sixteen patients with cervical cancer were performed intensity-modulated radiation therapy using offline cone beam computed tomography (CBCT) weekly during chemo/radiation. CTV was contoured on the planning CT. Each CBCT was rigidly registered to the planning CT with respect to bony anatomy. A pelvic MRI scan was performed before the radiation therapy and during the radiation dose of 9Gy/5f, 18Gy/10f, 27Gy/15f, 36Gy/20f, and 48.6Gy/27f. Those MRI images were compared with the first CT image, respectively. Changes of the target volume and spatial location were analyzed and evaluated for each patient by volume difference method and DICE similarity method. The gross tumor volume (GTV-T) changed significantly from 79.62cm3 to 20.86cm3 (average 73.80%). The clinical target volume (CTV) changed slightly from 672.59 cm3 to 608.26cm3 (average 9.56%). The volume of Uterus (CTV-T) changed slightly from 83.72cm3 to 80.23cm3. GTV-T and CTV decreased gradually with the increase in the number of radiation, and the change of GTV-T was the most obvious. There was also significant difference in GTV-T and CTV-T among different groups (P<0.001), but CTV was not significantly different in volume (P>0.05) and the change of GTV-T had a linear correlation with the number of radiation therapy (P<0.001). The mean volume changed rate(delta V%) of GTV-T, CTV-T and CTV varied from 23.05%, 4.71% and 5.84% to 70.85%, 6.78% and 9.59%.There was significant difference in GTV-T among different groups (P<0.001),and the change of GTV-T had a linear correlation with the number of radiation therapy (P<0.001). There was a negative correlation between ¢V% and DSC in target area and organs at risk (r<0, P<0.05). The DICE similarity coefficient (DSC) of GTV-T decreased with the increase of fractions during the course of radiation therapy (P<0.001). There was significant difference between DSC5f and DSC15f, DSC20f or DSC27f (P<0.05), however, there was no significant difference between DSC5f and DSC10f (P>0.05). Significant variations in tumor regression and spatial location occurred during radiation therapy of cervical cancer. The volume change rate and DSC of GTV-T were all linear correlated with the increase of the number of radiation. Adaptive radiation therapy approaches are needed to improve the treatment accuracy for cervical cancer.