60 y/o M with cT2N1M0 rectal adenocarcinoma located 6cm from anal verge


TECHNIQUE: He was treated with pre-op hypofractionated 3D-CRT with sequential chemo (capecitabine + oxaliplatin x 6 cycles) prior to total mesorectal excision (TME).
DOSE: He received 25 Gy in 5 fractions to peri-rectal, pre-sacral, and internal iliac nodes, with no boost to the primary/mesorectum.
  • IV contrast can help visualize vessels though not required (this patient had no IV contrast but extensive calcifications in vessels)
  • Radiopaque marker should be placed at the anal verge
  • Bladder comfortably full to help decrease small bowel dose
  • Consider small bowel and/or rectal contrast (optional)
  • Some institutions use prone position (belly board)
  • If using IMRT, supine position may be more reproducible
Alternative (per Myerson et al IJROBP 2014):
TECHNIQUE: Hypofractionated IMRT, with sequential adjuvant chemo prior to TME
DOSE: 20 Gy in 5 fractions to elective nodal target volume (per RTOG anorectal atlas), with 25 Gy in 5 fractions SIB to rectum and mesorectal compartment at levels of gross disease
Case contributed by National Cancer Institute / National Capital Consortium

RT coverage per RAPIDO Protocol
CTV = rectum and mesentery; peri-rectal, pre-sacral, internal iliac nodes*
  • Superiorly: bifurcation of internal iliac and external iliac arteries (~S1/S2). If any pre-sacral LN or internal iliac LN are involved, then CTV should be at least > 1 cm above most cranial pathologic LN.
  • Lateral border of mesentery: pelvic sidewall (muscle/bone)
  • Anteriorly: 1 cm into posterior bladder (for bladder variation above vagina/prostate) and include posterior portion of obturator nodes
  • Inferiorly: entire mesorectum to pelvic floor (even for upper rectal primary); ≥ 2cm inferior to gross disease; <3mm beyond levator ani (unless levator ani involved, then 1-2cm mgn up to bone) 
  • *Include external iliacs only if tumor extends to prostate/vagina (T4 tumor per AJCC)                    
    • External iliac vessels + 7-10 mm margin including small nodes
  • *If growth into distal vagina or growth into anal canal and distal to dentate line, include inguinals for anal canal involvement (controversial, inguinal nodes are metastatic in rectal cancer)
  • Avoid covering entire ischio-rectal fossa and anal canal unless tumor invades levators or anal canal, as additional toxicity is added
PTV = CTV + 0.7-1cm (except at skin)
CTV 20 = elective nodal target volume per RTOG anorectal atlas
CTV 25 = rectum and the mesorectal compartment over the length of involved rectum and peri-rectal LN, with a 1-cm margin cephalad and caudad
3D-CRT or IMRT are both considered standard of care for 5 Gy x 5 hypofractionated rectal radiation (RTOG 0822 showed IMRT did not reduce GI toxicity with conventionally fractionated RT).

Benefits of short-course RT:
  • Fewer visits for RT --> Increased cost effectiveness and decreased patient financial toxicity
  • Shorter time to diverting ileostomy time (if patient has been previously diverted)
  • Increased compliance with chemo
  • May allow for total neoadjuvant therapy (TNT) to spare post-op chemo toxicity
  • Response to neoadjuvant chemotherapy may help guide post-operative adjuvant treatment options
  • Rectum is ~15-16 cm long, starts ~S3
  • Rectum subdivided according to distance from anal verge during rigid sigmoidoscopy:
    • Upper 1/3: 12-16 cm
    • Middle 1/3: 6-12 cm
    • Lower 1/3: < 6 cm
  • Anterior peritoneal reflection is point at which rectum exits peritoneal cavity and becomes a retroperitoneal structure (12-15 cm from anal verge)
Dose constraints (per Myerson et al IJROBP 2014):
  • Target: 95% of PTV should be covered by at least 95% of Rx
    • Max dose 115% of Rx
  • OARs:
    • Bowel (maximum dose < 25 Gy, V20Gy < 50 cc)
    • Rectosigmoid largely included in CTV so not an avoidance structure
    • Include femoral head and neck

Daily Imaging:

  • Strongly consider DAILY cone beam CT given large fraction size
3D-CRT or IMRT are both acceptable; IMRT if using SIB technique or unable to meet OAR constraints with 3D-CRT:
  • See Case 11 for 3D-CRT 3-field technique