Room: AAPM ePoster Library
Purpose: CBCT imaging is routinely used to verify and correct for patient setup errors and to make adjustments to treatment plans if the anatomy deems to be significantly different from the original planning CT (pCT). In this study, we showed the feasibility of using CBCT and log files for automated dose monitoring and verification.
Methods: evaluated the use of the on-board kV-CBCT on a Varian Truebeam machine with SunNuclear PerFraction software to implement a CBCT-based dose verification workflow. The software uses clinical IGRT registration offsets to automatically fuse the CBCT dataset to the pCT resulting in a CT-CBCT merged patient anatomy and uses log files to calculate dose. First, a phantom was used to verify image registration accuracy. Then, data was collected on ten partial brain treatments to verify CBCT-based dose verification feasibility. Dose calculations were made directly on the pCT and compared with dose calculated on the CBCT with a customized CBCT-to-ED table. Dose was compared using 3D gamma analysis and dose differences between max point doses to the brainstem, chiasm, left and right globes.
Results: overall 3D gamma (using a 3%/3mm criteria) showed good agreement (on average 1.1% difference) between the dose calculation on CBCTs and pCTs. Additionally, no significant differences (all p > 0.05) were found in the maximum dose to the brainstem (2.0 cGy), chiasm (2.4 cGy), and left and right globes (0.3 cGy and 0.9 cGy) between the two datasets.
Conclusion: results from this study show that it is clinically feasible to use CBCT images in a clinical dose verification workflow. Since the images and log files are routinely acquired, and CT-CBCT fusion and dose calculation is automated, there is practically no additional burden to utilizing this method routinely. Additional testing is ongoing to investigate other treatment sites and different CBCT-to-ED calibration curves.