Figure 4: Axial CT slices for one representative patient. The left image shows the dose distribution without the rectal retractor and the right image with the retractor. The CTV is the red structure, the PTV is the light blue, and the rectal wall structure is in cyan. The isodose lines correspond to 40.6 Gy (green), 38.3 Gy (purple), 36.5 Gy (pink), and 36.5 Gy (yellow).