Fig. 1

Measurement of a perirectal distance at CTV center on axial CT image (a), and θ in 3-dimensional space on axial and sagittal CT images (a, b). The perirectal distance is measured at each vertex in a 4 × 4 cm coronal grid centered on the prostate midgland, at midline to generate a perirectal space map comprising up to 25 perirectal distance measurements for each patient (c)