eContour

35 y/o M with cT4N2M0 rectal adenocarcinoma w/ extension into the prostate and bilateral common, and internal and external iliac lymphadenopathy

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TECHNIQUE: 

He was treated with total neoadjuvant therapy, beginning with chemoradiation using IMRT with concurrent Xeloda followed by FOLFOX. Following treatment, given complete clinical response, surgery was deferred in favor of surveillance (per Fernandez et al. Lancet Oncol 2021).  

DOSE:

He received 45 Gy in 25 fractions to the pelvis with simultaneous integrated boost to involved pelvic nodes to 55 Gy, followed by sequential boost to 5.4 Gy in 3 fractions to the mesorectum (50.4Gy cumulative).  

SIMULATION:

  • PET/CT simulation was performed for better visualization of sidewall lymph nodes seen on MRI and to rule out distant metastatic disease
  • Patient was supine and immobilized using a vac bag
  • For male patients, consider a clamshell scrotal shield to minimize dose to testes
  • Daily IGRT with cone-beam CT or KV imaging is indicated, with cone-beam CT optimal given simultaneous integrated boost to gross nodal disease

 

Case contributed by UPMC

IMRT Contours for Node-Positive Rectal Cancer (per the RTOG Contouring Atlas)
  
GTVp: Visualized primary tumor on colonoscopy, PET/CT, and MRI
 
GTVn: FDG avid lymph nodes
 
CTV_LN:
  • Given nodal positivity, covered nodes up to level of distal common iliac (at least 5 mm above most cranial involved node), with 7-10 mm margin around the vessels
  • Inclusion of common iliac, internal/external iliac, presacral (including sacral foramina), and obturator lymph nodes
CTV_mesorectum:
  • Extend inferiorly to pelvic floor or at least 2 cm below GTV (whichever is more inferior)
  • Extend superiorly to rectosigmoid junction, and may therefore also include the presacral and lower internal iliac nodal basins
  • Posterior and lateral margins of mesorectum extend to lateral pelvic muscles or bone, with anterior extension into prostate gland/seminal vesicles/posterior bladder wall
  • Given involvement of prostate gland, additional anterior margin given in this case
CTV_45: CTV_LN + CTV_mesorectum
 
CTV_5.4: Entire mesorectum 1.5-2cm superior and inferior to GTV 
 
PTV: Respective CTV + 0.5-1cm

Total Neoadjuvant Therapy
  • Total neoadjuvant therapy has now become an accepted standard of care for patients with locally advanced rectal cancer based on recent data.
  • Surgical resection is currently the standard of care, but non-operative management with watchful waiting has increasingly been reported in the literature.  
  • PRODIGE 23 (Conroy Lancet Onc 2021) demonstrated improved pCR and DFS when comparing neoadjuvant chemotherapy followed by chemoRT therapy followed by surgery to preoperative chemoRT followed by surgery followed by adjuvant chemotherapy.   
  • RAPIDO (Bahadoer Lancet Onc 2020) demonstrated that preoperative short course RT followed by chemotherapy has improved pCR and DFS compared to preoperative chemoRT followed by surgery followed by optional adjuvant chemotherapy.
  • OPRA (ASCO 2020) demonstrated higher rates of organ preservation with chemoRT followed by consolidative chemotherapy when compared to induction chemotherapy followed by chemoRT, with similar rates of DFS and DM in both arms.  
  • Delivery of mFOLFOX6 after chemoradiation and before total mesorectal excision has the potential to increase the proportion of patients eligible for less invasive treatment strategies, per Garcia-Aguliar et al. Lancet Oncol 2015

Lateral Nodal Disease

  • Concensus guidelines recommend external iliac nodal coverage for lateral lymph node involvement or for cT4 tumors with anterior organ involvement (i.e. bladder, uterus, prostate)
  • Retrospective data (Ogura et al. JCO 2019) suggests that patients with lateral nodal disease are at much higher risk of lateral local recurrence following TME if they do not also undergo lateral lymph node dissection as these nodes are not routinely removed during TME.
  • Although prospective data is lacking, simultaneous integrated boost to 55-57.5 Gy to grossly involved pelvic nodes, while respecting bowel tolerance, has been demonstrated to be safe and feasible in rectal cancer and other pelvic malignancies and is appropriate alternative way to attempt to improve disease control in this patient cohort. 
  • SIB approach may not be feasible if using 3D planning and sequential boosts may be considered instead. 

Dose Constraints

  • Bone marrow: V20 Gy < 75%
  • Small bowel:
    • V35 Gy < 35%
    • V45 Gy < 200 cc
    • V55 Gy < 5 cc
  • Bladder: V40 Gy < 70%
  • Femoral heads: V25 Gy < 5%