This practical contouring guide walks through modern target delineation for a cT3N1 mid-rectal cancer undergoing long-course chemoradiation. Gone are the days of generous “box fields” for all—today’s approach is anatomy-driven and risk-adapted. The elective clinical target continues to routinely include mesorectal, presacral, internal iliac, and obturator nodes, with selective expansion to external iliac or inguinal basins based on tumor extent. Cranially, coverage begins at the common iliac bifurcation; caudally, it extends 2 cm below disease or to the pelvic floor. Boost volumes have tightened: rather than historical 2–3 cm margins, a 1 cm clinical target expansion on gross tumor is typical, with 0.5–1 cm around involved nodes. Dose to gross tumor follows intent—50–50.4 Gy for surgical cases versus at least 54 Gy for nonoperative management—with occasional escalation up to 60–66 Gy for unresected nodal disease. Interestingly, they continue to recommend prone positioning on a belly board when tolerated by a patient and employ a vaginal dilator or scrotal shelf when using supine positioning with full bladder to spare small bowel in all scenarios. | Pearce, Pract Radiat Oncol 2026
