A convolution method for calculating 10-MV x-ray primary and scatter dose including electron contamination dose

This paper has improved some of the weak points appearing in a previous article [A. Iwasaki, Med. Phys. 17, 203-211 (1990)] dealing with the calculation of 10-MV x-ray primary and scatter dose. The main improved points are as follows: (i) A pair of new functional equations expressing the primary dose spread array has been yielded. Consequently, the accuracy of the primary dose calculation both in the aluminum layer and in the soft tissue layer beyond the aluminum has been improved. (ii) A new functional equation expressing the backscatter factor has been developed. It has been utilized in the differential backscatter factor equation. Consequently, the calculated scatter dose spread array has been improved. (iii) A method of calculating the dose due to electron contamination has been introduced. With respect to the primary dose, the primary plus scatter dose, and the primary plus scatter plus electron contamination dose, it has been shown how the depth of maximum dose (dmax) varies with field size.