Radiation Field Modeling and Computerized Treatment Planning

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We are using a commercial vendor of video processor boards (GPUs) which are both substantially less expensive than the previous generation of custom volume rendering boards as well as having a greater potential for growth in performance. The commercial vendor also provides software (CUDA) for utilizing the boards for Monte Carlo calculations, which further supports our research objectives. We have transitioned from 3-dimensional image fusion to exploring 4-dimensional radiotherapy imaging. Our research has established a fundamental relationship between the temporal motion of the 3-dimensional external torso volume and those of internal organs, especially the lungs. Our research has developed a volumetric methodology for image tracking using external torso volume change for which a patent has been applied for. The Electron-Gamma Shower (EGS-4)-based Monte Carlo Dose Calculation Engine (DCE) has been fully implemented in both a LINUX and Windows environment. In the Windows environment, the DCE has been integrated into a full featured treatment planning system. Work is now centered on the development of phase-space source models. Currently, this system is used to investigate small field stereotactic radiosurgery. Due to the reduced field size, edge effects become important and the size of detectors used to access the radiation output affect the measurement results. Monte Carlo simulation of these output measurements greatly assisted in the selection of the detector system that is most suitable for these measurements. The Monte Carlo algorithm provided good agreement with experimental measurements down to applicators as small as 4mm. In a related project, we have adapted both algebraic and Monte Carlo DCEs to predict organ doses received from diagnostic CT scans. The characterization of the x-ray beam from a GE CT Scanner used for clinical scanning at Children's National Medical Center is complete. We have also completed absolute dosimetry measurements linking the standard diagnostic measurement of Computer Tomography Dose Index (CTDI) to actual absorbed dose. This includes a direct comparison of traditional CT dosimetry methodology versus the new CTDS to highlight the advantages of individualized dosimetry and demonstrate organ-specific dose descriptions. Our next goal is to undertake the commissioning of a helical fan-beam CT scanner using a small point-dosimeter, as opposed to the traditional measurement of CTDI employed in Diagnostic Radiology. It is hoped that this system will provide the framework for a more complete dose assessment of patient populations for epidemiological dose-response studies. ROB has embarked on a joint project with RRP, DCTD, NCI on the construction of a powerful computer that will make use of Field Programmable Grid Array (FPGA) boards to supplement the GPU cards to boost the computational power of the base computer by several orders of magnitude. Currently, the system has 35 FPGA cards and 4 GPUs in 5 expansion chassis. When fully functional, this should substantially reduce the time to complete a complex Monte Carlo calculation from weeks to minutes. ROB has experienced technical difficulties with the Hewlett-Packard (HP) Proliant Gen-10 server originally selected to perform as the host for the FPGA array. The current system BIOS is not compatible with the use of multiple PCIe expansion chassis that are necessary to accommodate all of the FPGA boards. A BIOS rewrite or upgrade will take around 2 years. As an alternative, ROB has acquired an OSS (One Stop Systems) 2U EOS server, which is guaranteed to support multiple PCIe expansion chassis, since they are all from the same vendor. This new system has been installed and is being tested and is currently configured for 32 FPGA cards and 2 GPU cards. The original HP server has been configured with a single PCIe expansion chassis (Trenton Systems), which hosts 4 FPGA cards and 2 GPU cards. The server BIOS will support a single PCIe chassis. This system will be utilized for software development and testing prior to exporting the finalized product to the production server.