Figure 1.

The sagittal view of a cervical cancer patient with a ring applicator in situ. The dose prescription point is ${\mathrm{P}}_{\mathrm{d}}$. D (in cm) is the distance between the outer wall of bladder and the center of the tandem and d (in cm) is the distance from point ${\mathrm{P}}_{\mathrm{d}}$ to the center of the tandem.