Purpose: To evaluate the feasibility of using a kilovoltage computed tomography (kVCT) subsystem on a novel radiotherapy machine with integrated CT and PET dual-imaging systems for treatment planning.
Methods: A CT quality phantom (CATPHAN model 504) was scanned with all kVCT scanning protocols on the new machine and on a clinical CT simulator with identical image geometry. Hounsfield unit (HU) linearity, consistency, and noise levels were evaluated, and density-to-HU tables were generated. An anthropomorphic phantom (CIRS Thorax Phantom) with heterogeneous lung and spine compartments was scanned on both the CT simulator and on the new machine using all scanning protocols. A volumetric modulated arc therapy plan was created on the phantom and copied onto each image set for dose calculation.
Results: The difference in average CT numbers for different density inserts on the CATPHAN phantom ranged from -3.5 to 5.7 HU between the CT simulator images and kVCT images on the new machine. The goodness-of-fit measure (R-squared) for HU linearity tests was 0.997 in all the CT images. The standard deviations (SDs) of the CT numbers for the density inserts ranged from 5.7 to 7.7 HU with the CT simulator images and ranged from 5.8 to 8.3 HU with high-dose protocols on the new machine. The SDs were lower with statistical significance when a higher-dose scan protocol was used. Compared to the plan dose based on the CT simulator images, the mean dose to the target and normal organs showed < 1% variation when the same plan was applied on kVCT images on the new machine.
Conclusion: The kVCT system on the new machine showed adequate CT image quality for treatment planning. This suggests that simulation and treatment may be performed in the same environment and that it may be possible to perform adaptive planning based on daily kVCT.
Funding Support, Disclosures, and Conflict of Interest: This research was supported by RefleXion Medical, Inc.
Not Applicable / None Entered.