Dose Calculation for Moving Field Therapy

Wheatley (1955) has recently published a method for X-ray depth dose calculation, readily applicable to moving field therapy. In his method the primary dose at a point is obtained from the product of two terms depending on the focal distance and tissue thickness, obtained from his Table III. The contribution given by scattered radiation is given by the product of six factors, of which five are obtained from his Table II and the sixth, the off-axis factor, from a previous publication (Worthley and Wheatley, 1952). In practice, it is somewhat tedious to measure or calculate the relevant variables, then look up the corresponding factors from tables, and it has been found possible to substitute charts from which the factors may be read directly.