Process and Initial Experience of Remote Credentialing of 3D IGRT Data for Institutions Participating in RTOG Clinical Trials

Abstract

To report the process and initial experience of a remote credentialing of 3D image-guided radiation therapy (IGRT) as part of quality assurance (QA) of submitted data by institutions participating in Radiation Therapy Oncology Group (RTOG) clinical trials. The following data sets were submitted through Image-Guided Therapy QA Center (ITC) from institutions for IGRT credentialing process as required by various RTOG trials: planning CT, plan, structures, positioning CT for one or a number of days, all in DICOM format. Daily shifts were also collected, along with descriptions of the imaging techniques. A centralized virtual environment is established at RTOG core laboratory containing analysis tools and database infrastructure for remote review by Physics Principal Investigators (Physics-PI). Appropriateness of IGRT technique (visibility of anatomical structures of interest) and volumetric image registration accuracy were evaluated. Registration accuracy was verified by repeat registration with a third party registration software and comparison with the institution's submitted data. With the accumulated review results, registration differences between those obtained by Physics-PI and from institutions were analyzed for different trial protocols (imaging sites), shift directions, and imaging modalities. This remote review process was successfully carried out for 87 3D cases (out of 137 total cases including 2D and 3D) during 2010. Differences of registration results between reviewers and institutions were 1.80 ± 1.06mm, 2.05 ± 1.05mm, 2.01 ± 0.93mm (mean ± SD; in left-right, superior-inferior, and anterior-posterior directions respectively) for lung cases; 0.69 ± 0.61mm, 2.89 ± 3.84mm, 0.40 ± 0.07mm for spine cases; and 1.52 ± 1.03mm, 2.51 ± 2.24mm, 1.45 ± 1.12mm for head and neck cases. The registration differences for kV CBCT cases were 1.73 ± 1.09mm, 1.59 ± 0.95mm, 1.74 ± 1.10mm, and for MVCT cases were 1.51 ± 0.98mm, 3.71 ± 1.67mm, 1.87 ± 0.86mm. Relatively large discrepancy in superior-inferior direction was found for MVCT cases due to the low spatial resolution (6mm slice spacing) in this direction for most MVCT cases. Major issues in repeating the registration included difficulty in reproducing initial patient setup position in some CBCT cases with pre-imaging couch shift and in some MVCT cases where the setup laser center was unknown. Additional information was requested from the institution if necessary and workarounds for these issues were developed. Preliminary review experience and clinical data indicated that remote review for 3D IGRT as part of QA for RTOG clinical trials is feasible and effective. Further improvements are expected to mature this remote evaluation process.