Refinement of operational health physics methodology using geographical information systems

The field of health physics draws upon other specialties for information and technologies relevant to emergency planning and radiation dose assessment. GIS has enjoyed only limited use in health physics to date, but as its applications are demonstrated and the computer hardware and software necessary for its implementation become less expensive, the widespread use by many health physicists is inevitable. This document presents a recommended protocol for the determination of population distributions around nuclear facilities for use as input data for estimating offsite radiation doses due to routine and accidental releases of radioactive materials. Techniques were developed to establish baseline population levels using U.S. Bureau of the Census data and GIS technology, construct current population estimates and future projections using the baseline data coupled with predictive equations and reconstruct past population distributions using current demographic databases. Concurrent to the fulfillment of these objectives is an accounting of uncertainties associated with procedures and parameters. These uncertainties propagate to yield a total uncertainty for the population which in turn is an input parameter for other models. The significance of this research is that techniques for spatial data analysis are described from a practical perspective. The reader is given the necessary information to choose a GIS platform, obtain population and street mapping data, transform those data into useful formats and interpret results. Proper interpretation of GIS analyses is also important for those professionals who contract with outside agencies for such services. Populations are reported as point estimates with no regard for error in GIS manipulation or input data. The problem stems from the resistance of software vendors to incorporate uncertainty accounting algorithms within their programs and reluctance to release proprietary codes to outside researchers. It is important for health physicists to realize that they can effectively perform many of their own GIS analyses, that the use of census levels that are too aggregated may drastically affect decisions based upon GIS output and that errors and uncertainties are generally ignored in the GIS industry and must be semi-quantitatively estimated.