P. Storchi et E. Woudstra, CALCULATION OF THE ABSORBED DOSE DISTRIBUTION DUE TO IRREGULARLY SHAPED PHOTON BEAMS USING PENCIL BEAM KERNELS DERIVED FROM BASIC BEAM DATA, Physics in medicine and biology, 41(4), 1996, pp. 637-656
In radiotherapy, accurately calculated dose distributions of irregular
ly shaped photon beams are needed. In this paper, an algorithm is pres
ented which enables the calculation of dose distributions due to irreg
ular fields using pencil beam kernels derived from simple basic beam d
ata usually measured on treatment units, i.e. central axis depth-dose
curves and profiles. The only extra data that are needed, and are not
currently measured, is the phantom scatter factor curve at the referen
ce depth. The algorithm has been developed as an extension to a previo
usly developed algorithm for rectangular fields which is based on the
Milan-Bentley storage model. In the case of an irregular field, the de
pth dose and the boundary function are computed by convolution of a fi
eld intensity function with pencil beam kernels. The depth dose is com
puted by using a 'scatter' kernel, which is derived from the stored de
pth-dose curves and from the phantom scatter factor curve. The boundar
y function is computed by using a 'boundary' kernel, which is derived
from the boundary profile of a number of large square fields. Because
of the simplicity of the data used and the underlying concepts, which
for instance do not separate the head scatter from the primary beam, t
his algorithm presents some shortcomings. On the other hand, this simp
licity is also of great advantage and the inaccuracy is acceptable for
most clinical situations.