Radiation dosimetric influence by different target volume definition in Cyberknife lung cancer and abdomen stereotactic body radiotherapy

Purpose: The dosimetric characteristics between four-dimensional with end-expiration and end-inspiration CT dose distributions of Cyberknifeare to be evaluated.Methods: A set of four dimensional (4D) CT images and two sets of CT scans,includingend-inspiration and end-expiration breath-hold, were obtained from 15 CyberKnife treated patients. Three internal target volumes (ITVs) were created from the three sequence images. Allpatients were treated using ITV-based strategy with an additional ITV-to-PTV margin of 3 mm.Results: In all of the 15 patients, the PTVfuse consistently has the smallest volumes compared to other PTV's. The nCI and coveragesof the plans were based on PTVfuse, which provided statistically significant differences for PTV4DE and PTV4DI. Additionally, the dose of normal tissue showed no statistical differences in the three type of plans (plan PTV4DE VS PTV4DI, p = 0.76), (plan PTV4DE VSPTVfuse, p = 0.23) and (plan PTV4DI VSPTVfuse, p = 0.16).Conclusion: The fusion of breath-hold sequences is beneficial to provide excellent target coverage than the end-inspiration or end-expiration with 4D-CT approach for target definition. Furthermore, the fusion of the end-expiration and end-inspiration CT scans may be used as an alternative to 4D CT in the absence of multi-modality images.