eContour

60 year-old female with high grade urothelial carcinoma invading the uterine wall, cervix and anterior vaginal wall, status post radical cystectomy, hysterectomy, bilateral salpingo-oophorectomy and anterior vagina resection. Pathology revealed multifocal positive margins with 12 of 35 examined lymph nodes involved, pT4a pN2 cM0 (Stage IVA).

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Technique:

  • IMRT is utilized on modern trials and reduces toxicity to bowel compared to 3D CRT (NRG-GU001)

Dose

  • This patient was treated to 50.40Gy in 28 fractions to the CTV cystectomy bed and CTV nodes.
  • Per NCCN 2023: Treat post-operative areas at risk for microscopic disease 45Gy to 50.4Gy in 180 cGy daily fractions; involved resection margins and areas of extranodal extension can be boosted to 54-60 Gy; Areas of gross residual disease should be boosted to 66–70 Gy if feasible. Concurrent chemotherapy can be considered.

Simulation:

  • Supine, head neutral, arms crossed, immobilize legs with knee/foot lock
  • Obtain CT from L2 to mid-thigh
  • Isocenter can be placed at the center of pelvis
  • Note, this patient’s bowel was severely distended due to opioid induced constipation post-operatively. Ideally, the patient would be simulated with an empty bowel. 

 

Per 2022 IBIS Update of Consensus Guidelines

 

CTVcb (cystectomy bed):

  • Superior: 2 cm above the superior aspect of the pubic symphysis
  • Inferior: Male patients: 2-3 mm superior to penile bulb. Female patients: 1 cm below inferior pole of obturator foramen
  • Anterior: Posterior aspect of pubic symphysis and planes extending superiorly and inferiorly from posterior aspect of pubic symphysis
  • Posterior: Anterior one-third aspect of anorectal circumference and plane extending superiorly from anterior border of rectum
  • Lateral: Medial border of obturator internus muscle and prostate bed or vaginal wall

*A more extensive CTV may be preferable to include surgical clips or in the case of extranodal tumor involvement.

*Do not crop CTV to bowel

 

CTVn (nodes)

Presacral nodes:

  • Superior: Lumbosacral joint (L5-S1)
  • Inferior: Inferior aspect of S3
  • Anterior: 1-1.5-cm anterior to sacrum, Posterior: Sacrum, Lateral: Right and left common iliac vessels

Iliac nodes:

  • Superior: Iliac vessels from bifurcation of the abdominal aorta
  • Inferior: External iliac: superior aspect of femoral heads. Internal iliac: point of exit through greater sciatic notch or no longer visible on CT
  • Anterior/Posterior/Lateral: 7-mm expansion around iliac vessels

Obturatornodes

  • Superior: Bifurcation of common iliac vessels
  • Inferior: Superior aspect of pubic symphysis
  • Anterior: Anterior edge obturator internus muscle
  • Posterior: Posterior edge obturator internus muscle
  • Lateral: 1.9-cm medial to obturator internus muscle (no cropping to the bowel)

CTV to PTV margins: uniform 0.5 to 0.7 cm expansion

 

Per 2016 Contouring Guidelines

The urinary diversion OAR is contoured to avoid bringing beams directly through this structure, without compromising target coverage. 

  • Non-continent diversion with a bowel conduit: include the stoma and the visible portion of the bowel conduit
  • Continent nonorthotopic catheterizable diversion (“Indiana pouch”): include the stoma, bowel conduit, and internal urine reservoir.
  • Continent orthotopic diversion (“Studer pouch”): include the bowel reservoir.

 

  • A major change in the 2022 update is to include the cystectomy bed in the CTV regardless of margin status, and to not crop the CTV to the bowel. This update is due to evidence showing that there is a high rate of cystectomy bed recurrence regardless of margin status, and that there are low rates of cystectomy bed failure when it is included.
  • 2022 contouring guidelines reflect NRG-Oncology practices lymph node delineation for prostate and cervical cancer: the anterior and posterior edge of the obturator internus muscle mark the ant-post borders of the obturator region; take the inferior border of the presacral region to the bottom of S3.
  • Multidisciplinary approach with the surgeon is important, as relapse can be due to seeding from surgical clips that are located at the edges of the radiation field. Consider extending the CTV to include surgical clips.