Feasibility of Improving the Accuracy of Dose Calculation Using Hybrid Computed Tomography Images: A Phantom Study

Purpose: Kilovoltage computed tomography (kV-CT) is essential for radiation treatment planning.However, kV-CT images are significantly distorted by artifacts when a metallic prosthesis is present in the patient's body.Thus, the accuracies of target delineation and treatment dose calculation are inevitably lowered.We evaluated the accuracy of the calculated doses using an image restoration method with hybrid CT, which was introduced in our previous study. Methods:A cylindrical phantom containing four metals, namely, silver, copper, tin, and tungsten, was scanned using kV-CT and megavoltage CT to produce hybrid CT images.We created six verification plans for three head and neck patients on kV-CT and hybrid CT images of the phantom and calculated their doses.The actual doses were measured with film patches during beam delivery using tomotherapy.We used the gamma evaluation method to compare dose distribution between kV-CT and hybrid CT with three gamma criteria, namely, 3%/3 mm, 2%/2 mm, and 1%/1 mm. Results:The gamma pass rates decreased as the gamma criteria were strengthened, and the pass rate of hybrid CT was higher than that of kV-CT in all cases.When the 1%/1 mm criterion was used, the difference in gamma pass rates between them was up to 13%p.Conclusions: According to our findings, we expect that the use of hybrid CT can be a suitable approach to avoid the effect of severe metal artifacts on the accuracy of dose calculation and contouring.