Figure 1.

Three sources (A is active, and B and C are inactive sources) are used to derive the perturbation (P‐value) and ISA formulism (ISA‐value). These sources are places in coordinate plane of (R, Z) in away and along format. Other dimension is constant (0.25 cm) and is from $-0.125$ to 0.125 cm. The dose data are obtained in any voxels with dimension of $0.25\times 0.25\times 0.25\hspace{0.17em}{\mathrm{c}\mathrm{m}}^3$. The R and Z dose distances are from $-10$ to 10 cm for all calculation cases.