An equivalent squares template

A template for calculating equivalent squares of irregularly shaped fields is described. Calculations using the template are essentially scatter summations. Comparisons with a computer program showed good agreement in equivalent squares and tumor doses (within 0.8%). Comparisons with area-perimeter ratio methods of computing equivalent squares showed consistently better accuracy using the template. For highly irregular fields, the template calculation required 3-10 min for central axis computation, comparable to that required by the other manual methods.