Applying the FAST Standard for TG-51 Spreadsheet Design

Abstract

Similar to the financial modeling industry, the medical physics community is heavily reliant upon spreadsheets to perform complex calculations. Based on a survey performed as part of the current study, 95% of the respondent clinics calibrated the output of their linear accelerator (via the TG-51 protocol) using spreadsheets. With accuracy being paramount in financial modeling, the industry implemented the FAST Standard (Flexible, Appropriate, Structured, and Transparent) to specifically address the concern with good spreadsheet design and error mitigation. No such standard has been applied in the field of medical physics, in fact, of the clinics surveyed, 50% did not perform second checks of the results returned from their spreadsheets. In the current study, medical physics-applicable aspects of the FAST Standard are introduced, and the behavior concerning these aspects evaluated following completion of surveys. By highlighting these aspects of the FAST Standard, as well as the current deficiencies regarding its use, clinics can reduce the introduction of error associated with the use of spreadsheets. Two surveys were distributed to the medical physics community. The first survey accessed the general process for performing a TG-51 calibration, including the use of spreadsheets and the process of second checking. The second survey addressed the use of spreadsheets with specific emphasis placed on principles of the FAST Standard. Based on FAST principles, it is recommended that all factors be calculated only once, that a normally-positive convention be used on working sheets, that a separation be made between interface and presentation sheets, that links between sheets be minimized, that cells are not hidden, that presentation sheets are used to present results, that formulas or kept short, that formulas do not embed constants, that parenthetic separation not be used in formulas, and that changes of the spreadsheet be documented via version control. Currently, only 12% of clinics surveyed comply with at least 75% of the FAST Standards presented here, and 32% of clinics are in compliance with at least 50% of the FAST Standards presented herein. Notable deficiencies include a lack of version control, the use of linked sheets, the non-use of a normally positive convention, the lack of presentation sheets, and the lack of an instruction sheet. By following the lead of the financial modeling industry, the implementation of the FAST Standard within the medical physics community can have the effect of error reduction in processes which rely on accurate and well-designed spreadsheet design.