Figure 2.

One example patient plan (Patient 4 at 80% prescription isodose level) showing the average dose in each rind structure as a function of the distance from the surface of the planning target volume (PTV). The fitted values of Equation (1) were a₁ = 18.43 (Gy), a₂ = 4.218 (Gy), b₁ = 0.2477 (mm⁻¹) and b₂ = 0.04334 (mm⁻¹).