Calibration and validation of kv-CBCT in room imaging for dose calculation and adaptive radiotherapy

Op verzoek van Jelle Scheurleer: Purpose: To investigate the accuracy of dose calculation on cone beam CT (CBCT) data sets after HU-RED calibration and validation in phantom studies and clinical patients. Material and methods: Calibration of HU-RED curves for kV-CBCT were generated for three clinical protocols (H&N, thorax and pelvis) by using a Gammex RMI phantom with human tissue equivalent inserts and additional perspex blocks to account for patient scatter. Two calibration curves per clinical protocol were defined, one for the Varian Truebeam 2.0 and another for the OBI systems (Varian, Palo Ato). Differences in HU values with respect to the CT-calibration curve were evaluated for all the inserts. Four radiotherapy plans (breast, prostate, H&N and lung) were produced on an anthropomorphic phantom (Alderson) to evaluate dose differences on the kV-CBCT with the new calibration curves with respect to the CT based dose calculation. Dose differences were evaluated according to the D2%, D98% and Dmean metrics extracted from the DVHs of the plans and - evaluation (2%, 1mm) on the three planes at the isocenter for all plans. Clinical evaluation was performed on 5 patients and dose differences were evaluated as in the phantom study