Radiation Field Modeling and Computerized Treatment Planning

Division Of Clinical Sciences - Nci

Investigators

Linked publications & trials

Abstract

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. In addition to the HPE Proliant DL-580 Gen 10 server, 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 (Colossus II) has been installed and is being tested and is currently configured for 30 FPGA cards and 2 GPU cards. The original HP server (Colossus I) 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. Two factor authentication (2FA) has been installed on Colossus I, to permit access by approved extramural individuals so that they can facilitate code development. We have replaced the OSS 2U EOS server with an entirely new unit (at no cost to the Government) due to an electrical overload causing irreversible damage. The advent of COVID-19 is still impacting the progress of this project and staff have only recently returned to full time work in-house. CBIIT has lost all of its LINUX support staff, which also inhibits on-site support availability to assist with resolving issues. Although a new person has been recruited, there is still a significant learning curve involved. Additionally, the CBIIT-mandated LINUX operating system (RHL 7) does not support the drivers needed for multiple FPGA boards. We have only just received permission to upgrade to RHL 8.