Dosimetric evaluation of four‐dimensional dose distributions of CyberKnife and volumetric‐modulated arc radiotherapy in stereotactic body lung radiotherapy

Advanced image‐guided stereotatic body lung radiotherapy techniques using volumetric‐modulated arc radiotherapy (VMAT) with four‐dimensional cone‐beam computed tomography (4D CBCT) and CyberKnife with real‐time target tracking have been clinically implemented by different authors. However, dosimetric comparisons between these techniques are lacking. In this study, 4D CT scans of 14 patients were used to create VMAT and CyberKnife treatment plans using 4D dose calculations. The GTV and the organs at risk (OARs) were defined on the end‐exhale images for CyberKnife planning and were then deformed to the midventilation images (MidV) for VMAT optimization. Direct 4D Monte Carlo dose optimizations were performed for CyberKnife ( 4 D CK ). Four‐dimensional dose calculations were also applied to VMAT plans to generate the 4D dose distributions ( 4 D VMAT ) on the exhale images for direct comparisons with the4 D CK plans.4 D CK and4 D VMAT showed comparable target conformity ( 1.31 ± 0.13 vs. 1.39 ± 0.24 , p = 0.05 ). GTV mean doses were significantly higher with4 D CK . Statistical differences of dose volume metrics were not observed in the majority of OARs studied, except for esophagus, with4 D VMAT yielding marginally higher D 1 %than4 D CK . The normal tissue volumes receiving 80%, 50%, and 30% of the prescription dose ( V 80 % , V 50 % , and V 30 % ) were higher with4 D VMAT , whereas4 D CK yielded slightly higher V 10 %in posterior lesions than4 D VMAT . VMAT resulted in much less monitor units and therefore greater delivery efficiency than CyberKnife. In general, it was possible to produce dosimetrically acceptable plans with both techniques. The selection of treatment modality should consider the dosimetric results as well as the patient's tolerance of the treatment process specific to the SBRT technique. PACS numbers: 87.53.Ly, 87.55.km