Evaluation of kV-CBCT based 3D dose calculation accuracy and its validation using delivery fluence derived dose metrics in Head and Neck Cancer

Purpose: The purpose of this study is to evaluate the dosimetric impact of Hounsfield unit (HU) variations in kilovoltage cone-beam computed tomography (kV-CBCT) based 3D dose calculation accuracy in the treatment planning system and its validation using measured treatment delivery dose (MTDD) derived dose metrics for Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiotherapy (IMRT) plans in Head and Neck (HN) Cancer. Methods: CBCT dose calculation accuracy was evaluated for 8 VMAT plans on inhomogeneous phantom and 40 VMAT and IMRT plans of HN Cancer patients and validated using ArcCHECK diode array MTDD derived 3D dose metric on CT and CBCT. Results: The mean percentage dose difference between CBCT and CT in TPS (Delta D(CBCT-CT)(TPS)) and 3DVH (Delta D (CBCT-CT)3DVH) were compared for the corresponding evaluation dose metrics (D-98%, D-95%, D-50%, D-2%, D-max, D-1cc, D-0.03cc, D-mean) of all PTVs and OARs in phantom and patients. Delta D(CBCT-CT)(TPS) and Delta D(CBCT-CT)(3DVH) for all evaluation dose points of all PTVs and OARs were less than 2.55% in phantom and 2.4% in HN patients. The Pearson correlation coefficient (r) between Delta D(CBCT-CT)(TPS) and Delta D(CBCT-CT)(3DVH) for all dose points in all PTVs and OARs showed a strong to moderate correlation in phantom and patients with p < 0.001. Conclusions: This study evaluated and validated the potential feasibility of kV-CBCT for treatment plan 3D dose reconstruction in clinical decision making for Adaptive radiotherapy on CT in Head and Neck cancer.