A Delivered Dose–Based Record and Verify System in the Era of IGRT

Abstract

Purpose/Objective(s): Computerized Record and Verify System (RVS) has been used to detect and prevent mistakes in the delivery of external beam radiation therapy for more than 20 years. Conventional dose tracking mechanism in RVS is monitor unit (MU) based, assuming patients are treated exactly as planned. Without incorporating parameters such as machine behavior, patient setup, and patient anatomy, the cumulative doses do not accurately represent the actual doses delivered to patients, which is the goal of a RVS. We developed an automatic system to compute and accumulate daily doses through re-computation using daily imaging, and verify dose volume information in the context of RVS. Materials/Methods: Our system consists of several components, including a DICOM data retriever, dosimetric computation engine, and review platform. The workflow begins after each treatment; the DICOM daemon automatically retrieves daily volumetric images from patient records. The delivered dose is computed using a convolution-superposition based dose calculator implemented in-house on graphic cards. The deformation field between the daily and planning CT is computed using Morphons algorithm to warp the planning structures and delivered doses. The dose volume histograms of the daily and cumulative doses are generated for dose tracking and reporting. These data are queryable and a triggering system using a configurable tolerance table can be set up to prompt a clinical review. Possible root causes are analyzed such as machine output drifting, patient set up error. A user-friendly 4D image viewer is integrated for efficient review of images and doses. Results: Various aspects of the system were validated. Our dose calculator passed 97% gamma test evaluated in 3D with 2% dose difference and 2mm distance-to-agreement compared with tomotherapy calculated dose. With proper calibration of the imaging systems on tomotherapy machines, recomputed daily doses agreed with measurements in phantom within 2% for all jaw sizes. Visual inspection shows acceptable and consistent deformable registration results, except for cases with large or unrealistic deformations. This system is used clinically and more than 35,000 fractions were computed. More than 50 incidences, which would otherwise not be caught with conventional MU-based dose tracking system, were detected. The automatic triggering system is able to detect significant patient setup errors and anatomical changes. Conclusions: We developed a system to automatically accumulate and verify the actual distribution of delivered dose over the course of radiation therapy. This system helps detect and prevent further deviations in treatments, quantifies the dosimetric impact of the deviations, provides necessary information for adaptive radiation therapy, and hence is invaluable in improving the quality of patient care. Author Disclosure: X. Mo: None. Y. Chen: None. M. Chen: None. D. Parnell: None. S. Key: None. W. Lu: None. G. Olivera: None. D. Galmarini: None.