Target volume and artifact evaluation of a new data driven 4D CT

Publication date: Available online 2 February 2017
Source:Practical Radiation Oncology
Author(s): Rachael Martin, Tinsu Pan
Purpose4D CT is often used to define the internal gross target volume (IGTV) for radiation therapy of lung cancer. Traditionally, this technique requires the use of an external motion surrogate, however, a new image data driven 4D CT has become available. This study aims to describe this data driven 4D CT and compare target contours created with it to those created using standard 4D CT.MethodsCine CT data of 35 patients undergoing SBRT were collected and sorted into phases using standard and data driven 4D CT. IGTV contours were drawn using a semi-automated method on maximum intensity projection (MIP) images of both 4D CT methods. Errors due to reproducibility of the method were characterized. A comparison of phase image artifacts was made using a normalized cross correlation method which assigned a score from +1 (data driven "better") to −1 (standard "better").ResultsThe volume difference between the data driven and standard IGTVs was not significant (data driven was 2.1±1.0% smaller, p=0.08). The Dice similarity coefficient (DSC) showed good similarity between the contours (0.949±0.006). The mean surface separation was 0.4±0.1mm and the Hausdorff distance was 3.1±0.4mm. An average artifact score of +0.37 indicated the data driven method had significantly fewer and/or less severe artifacts than the standard method (p=1.5e-5 for difference from 0).ConclusionOn average, the difference between IGTVs derived from data driven and standard was not clinically relevant or statistically significant, suggesting data driven 4D CT can be used in place of standard 4D CT without adjustments to IGTVs. The relatively large differences in some patients were usually attributed to limitations in automatic contouring or differences in artifacts. Artifact reduction and setup simplicity suggest a clinical advantage to data driven 4D CT.



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