Table 3.

Summary of elective CTV recommendations of different contouring guidelines for IMRT in critical regions of anal cancer

	CTV delineation recommendations
	Cranial (internal & external iliac nodes/mesorectal)	Caudal (inguinal)	Ischiorectal fossa
RTOG 2009 [8]	Mesorectal - Rectosigmoid junction or 2 cm superior to superior extent of gross disease (rectum/perirectal nodes) Internal & external iliac nodes - The most cephalad aspect of CTV: bifurcation of common iliac vessels into external/internal iliacs (approximate boney landmark: sacral promontory)	- Always elective coverage of inguinal and external iliac region - inferior: 2 cm caudal to the saphenous/femoral junction. - “The inguinal/femoral region should be contoured as a compartment with any identified nodes (especially in the lateral inguinal region) included.”	- If no tumor extension into ischiorectal fossa: CTV just a few millimetres beyond the levator muscles - Advanced anal, extending through the mesorectum or the levators: “~ 1–2 cm margin up to bone wherever the cancer extends beyond the usual compartments.”
BNG 2016 [12]	Internal & external iliac nodes - Cranial internal, external iliac and pre-sacral space: “bifurcation of the common iliac artery into the external and internal iliac arteries (usually corresponds to the L5/S1 interspace level)” Mesorectal - If no mesorectal nodes: The lower 50 mm of the mesorectum. - If involved mesorectal nodes: The level of the recto-sigmoid junction	- Should be added as a compartment - Superficial and deep inguinal nodes of the femoral triangle and visible benign LN or lymphoceles outside these boundaries. - Borders: lateral: medial edge of sartorius or ilio-psoas, medial: spermatic cord in men. Posterior: pectineus, adductor longus and iliopsoas. Anterior: 5 mm from skin. Inferior: lesser trochanter.	No direct recommendations for the ischiorectal fossa. CTV gross tumor of locally advanced tumors: - CTV_A = GTV + 15 mm
AGITG 2011 [11]	Internal & external iliac nodes “Cranial: bifurcation of the common iliac artery into the external and internal iliac arteries (usually corresponds to the L5/S1 interspace level)” “The sacral promontory, defined at the L5/S1 interspace” Mesorectal “Cranial: the level of the recto-sigmoid junction; best identified where the rectum runs anteriorly to join the sigmoid colon (Atlas 4b).”	- Inclusion of superficial and deep inguinal LN of the femoral triangle and any visible LN or lymphoceles. Borders: inferior: “there is no consensus”, so compromise: lower edge of the ischial tuberosities. Posterior: muscles, anterior: minimum 20-mm margin on the inguinal vessels, including any visible LN or lymphoceles, lateral: medial edge of sartorius or iliopsoas, medial: a 10- to 20-mm margin around the femoral vessels. The medial third to half of the pectineus or adductor longus muscle serves as an approximate border.	- Cranial: levator ani, gluteus maximus, and obturator internus, caudal: suggestion: level of the anal verge. Lateral: ischial tuberosity, obturator internus, and gluteus maximus muscles. Anterior: fusion of anal sphincters. Inferiorly: 10 to 20-mm anterior to the sphincter muscles. Posterior: a transverse plane joining the anterior edge of the medial walls of the gluteus maximus muscle.