Rectal Ca Radiation Technique

Must know in Rectal Ca Radiation:

  • Mesorectum:
    • Cylindrical, cone shaped structure
    • Adipose tissue with lymphovascular and neural structures
    • Encapsulated by fascia
    • Cranio-caudal
      • Cranial tip —> Sacral Promontory
        • at origin of sup rectal a.
      • Caudal tip —> where levator ani m. inserts into the rectal wall
        • OR when Inf mesentrci a. bifurcates into:
          • Sigmoid a.
          • Upper rectal a.
    • Below dentate line —> matches levator ani m.
    • Above dentate line —> Piriform m. bounds the fascia on both sides
    • Anteriorly —> Denonvillier fascia
      • Pos wall of prostate/Sem Ves in men
      • Pos Vaginal wall/Uterus in women
  • Pre-sarcral space ( posterior pelvic subsite )
    • Post border —> Waldeyer's fascia (presacral fascia)
    • Ant border —> Mesorectal fascia
    • Contain:
      • Median and lateral sacral vessels
      • Pre-sacral LN
      • Ant branches of sacral n.
      • Inf hypogastric plexus
  • Lateral Pelvic subsite —> Area lat to mesorectum to lateral pelvic wall
  • Inferior pelvic subsite
    • Anal triangle of perineum
      • Anal sphincter
      • Peri-anal space
      • Inschiorectal space
  • Anterior pelvic subsite:
    • All pelvis organs that locate anteriorly to mesorectum

  • Lymph node regions:
    • Mesorectal LN
      • LN along Sup Rectal a.
    • Upward LN
      • LN along Inf Mesentric a.
    • Lateral LN
      • LN along:
        • Middle Rectal a.
        • Obturator
        • Int. Iliac a.
    • External iliac LN
    • Inguinal LN

Pelvic Subsite Rate of Recurrence post Surgery(no RT)
Pre-Sacral 40%
Lateral Pelvic 20%
Ant Pelvic Organs 5%
Inf Pelvic
<6cm from anal margin 10%
6-11cm 5%
>11cm None

LN Chance of LN+ Comment
MesoRectal 90% none >4cm
Inf mesentric a. 50% upward LN
Lateral 30% Low seated tumours > High and middle seated
Middle Rectal a. & Obturator & Int. Iliac a.
External and Inguinal 5% High if tumour close to anal verge

  • GTV is GTV ….
  • Now you should be simply ready to decide where to include in CTV
    1. Mesorectum
      • Mesorectum will be resected completely by surgery.(TME)
      • Pathologist would require an intact margin to call complete resection.
    2. Pre-Sacral region
      • Independent of tumour location
      • always should be in CTV
      • A triangular shaped area:
        • Apex —> Coccyx
        • Ant: mesorectum
          • Mesorectum is hard to see in CT
            • ==> 1cm ant to sacrum
        • Post: Sacral bones
        • Base: Sacral promontery
    3. When to include inferior pelvic subsite:
      1. Tumour within 6cm of anal margin
      2. Tumour invading the sphincter
        • APR will be necessary
      3. Lateral borders —> Int obturator m. and Ischium
    4. Inferior Mesentric LN ( Upward LN )
      • If tumour is above peritoneal reflection
    5. Internal Iliac and obturator
      • all patients but middle and lower rectum more
      • Some suggest that one can omit obturator if tumour is >10cm above anus
    6. External Iliac and Inguinal
      • Include external iliac if tumor invades bladder, vagina, prostate, or cervix

Rectal RT in other words!