Abstract
Purpose: To quantify the dose calculation accuracy achievable with 3D anatomical images obtained by Megavoltage Cone‐Beam Computed Tomography (MVCBCT) for the head and neck region (H&N). Method and Materials: MVCBCT images of inserts of different density immersed in water were obtained. This allowed the tuning of the parameters used for the image reconstruction. A MVCBCT number versus material density curve was also extracted for dose calculation purposes. MVCBCT images of a Rando phantom head were then acquired on a linac treatment couch with two different gain image calibrations and in two different positions relative to the room isocenter. Voxel‐based and band‐pass filter cupping artifact reduction methods were applied on all MVCBCT images. Images of the same phantom were also obtained with a kVCT. All images were transferred to a treatment planning system and dose calculations performed with various beam configurations. The dose differences obtained with the kVCT images and the MVCBCT images were analyzed using a gamma index function. Results: At best, 96.1% and 98.8% of the dose points calculated with the MVCBCT images were within the dose calculated with the kVCT image by [2%, 2 mm] and [3%, 3 mm], respectively. The worst cases observed had fractions of 87.7% and 96.3% of the dose points that agreed within [2%, 2 mm] and [3%, 3 mm], respectively. The cupping artifact reduction methods tested did not significantly improve the dose calculation for most cases. Conclusion: With proper calibration, dose calculations with MVCBCT images in the H&N region are feasible with an accuracy of [3 %, 3 mm] or less. The cupping artifact for H&N imaging does not lead to important dose calculation errors. Dose calculation with patient MVCBCTs and treatment plans are ongoing. Conflict of Interest: Research sponsored by Siemens OCS.
Published Version
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