Detecting The Variations Of The Spatial Position And Overlap Ratio For Pancreatic Cancer Target During Concurrent Radiochemotherapy Based On Repeated Contrast Enhanced Ct Scans

Purpose/Objective(s): To investigate the target variations of the spatial position and overlap ratio for pancreatic cancer with contrast enhanced computed tomography (CECT) scanning during concurrent radiochemotherapy. Materials/Methods: 20 patients with unresectable pancreatic tumor performed CECT scan before radiation therapy and at the 15th fraction (2 Gy per fraction). The two CT data sets of each patient were registered using software tools in the radiation treatment planning system on the basis of bony landmarks. The GTV was delineated by the same radiotherapist on each CECT image, the volume and the coordinate of the GTV were acquired from the treatment planning system. Results: Larger displacements (Pu003c0.01) were observed in the superioreinferior direction with a mean value of 0.70cm, compared with 0.37cm and 0.37cm in the right-left and anterioreposterior direction, respectively. However, the variations of GTV centroid displacements in the same direction did not reach statistical significance during radiation therapy. The GTV decreased 26.62% (PZ0.001) at the 15th fraction (30 Gy). The degree of inclusion (DI) between the two scans was 0.55, the matching index (MI) was 0.47, the three dimensional vector of the GTV negatively correlated with the DI and MI (rZ-0.657, -0.702; PZ0.002, 0.001, respectively). Conclusion: Under the treatment of the concurrent radiochemotherapy, significant variations were observed in the position and the volume for the unresectable pancreatic tumor. The target displacement, deformation and regression lead to the decrease of the overlap ratio relative to the initial target. Author Disclosure: J. Wang: None. J. Li: None. J. Sun: None. Y. Zhang: None.