Implementation of remote 3-dimensional image guided radiation therapy quality assurance for radiation therapy oncology group clinical trials.

PURPOSE: To report the process and initial experience of remote credentialing of three-dimensional (3D) image guided radiation therapy (IGRT) as part of the quality assurance (QA) of submitted data for Radiation Therapy Oncology Group (RTOG) clinical trials; and to identify major issues resulting from this process and analyze the review results on patient positioning shifts. METHODS AND MATERIALS: Image guided radiation therapy datasets including in-room positioning CT scans and daily shifts applied were submitted through the Image Guided Therapy QA Center from institutions for the IGRT credentialing process, as required by various RTOG trials. A centralized virtual environment is established at the RTOG Core Laboratory, containing analysis tools and database infrastructure for remote review by the Physics Principal Investigators of each protocol. The appropriateness of IGRT technique and volumetric image registration accuracy were evaluated. Registration accuracy was verified by repeat registration with a third-party registration software system. With the accumulated review results, registration differences between those obtained by the Physics Principal Investigators and from the institutions were analyzed for different imaging sites, shift directions, and imaging modalities. RESULTS: The remote review process was successfully carried out for 87 3D cases (out of 137 total cases, including 2-dimensional and 3D) during 2010. Frequent errors in submitted IGRT data and challenges in the review of image registration for some special cases were identified. Workarounds for these issues were developed. The average differences of registration results between reviewers and institutions ranged between 2 mm and 3 mm. Large discrepancies in the superior-inferior direction were found for megavoltage CT cases, owing to low spatial resolution in this direction for most megavoltage CT cases. CONCLUSION: This first experience indicated that remote review for 3D IGRT as part of QA for RTOG clinical trials is feasible and effective. The magnitude of registration discrepancy between institution and reviewer was presented, and the major issues were investigated to further improve this remote evaluation process.

Lung cancer radiation therapy: Monte Carlo investigation of "under dose" by high energy photons.

Loss of electronic equilibrium in lung tissue causes a build-up region in the tumor. Increasing the photon energy increases the depth at which electronic equilibrium is reestablished within the lung tumor. This study uses the Monte Carlo code PENELOPE for simulations of radiation treatment of tumor surrounded by lung. Six MV photons were compared to 15 MV photons using four beam arrangements in both homogeneous and heterogeneous media. The experimental results demonstrate that for every beam arrangement in heterogeneous media 15 MV photons delivered 5% to 10% lower dose to the tumor periphery than 6 MV photons. The simulations also show that in axial coplanar treatment plans, the loss of electronic equilibrium was greatest in the coronal plane. In conclusion there is a tumor sparing effect at the tumor-lung interface that is a function of beam energy. As an alternative to increasing beam energy, the addition of multiple beam angles with lower energy photons improved target coverage. If higher energy beams are required for patients with large separation, then adding multiple beam angles does offer some improved target coverage. The non-coplanar technique with the lower energy photons covered the tumor with a greatest isodose at the tumor periphery without tangential sparing in the coronal plane.