eContour

78F with a history of morbid obesity, COPD, CHF, and current smoker with FIGO Stage IB (cT1b cN0 M0) G2 endometroid-type endometrial adenocarcinoma deemed to be too high risk for surgery as well as a brachytherapy procedure.

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Rx: 4500cGy in 25 fractions followed by boost to 3000cGy in 6 fractions.

Sim/Planning:

  • Sim 1: 2 hours pre-sim drank 1 bottle or oral contrast. 1 hour before CT sim drank 8oz of water. CT simulated supine, with square cushion between feet both full and empty bladder.
  • Sim 2: MRI pelvis obtained prior to Sim 2 and fused.

Contours per Small IJROBP 2021.

Common iliac nodal CTV: 7mm uniform margin surrounding the right and left common iliac artery and vein excluding bone and muscle.

  • Include any suspicious LNs and any pertinent surgical clips.
  • The CTV margin should increase to 1cm at the midpoint of the common iliac chain anterior to the vessels while abutting the iliopsoas laterally.

Presacral Nodal CTV: The presacral nodal CTV should be a relatively fixed strip of tissue measuring 1 to 1.5cm wide in a plane perpendicular to the face of the sacral bodies.

  • The superior aspect of the presacral nodal CTV is contiguous with the CI nodal CTV.
  • If bowel is present, the CTV might extend a few mm into the bowel loops that might intermittently move into the presacral nodal CTV.

External iliac nodal CTV: Superiorly begins at the bifurcation of the CI vessels and should comprise a uniform 7mm margin placed around the vessels, not extending into bone or muscle and up to 10mm anteriorly.

  • The inferior aspect of the external iliac arteries is where the deep circumflex artery branches and where the external iliac vessels course laterally as they leave the pelvis to become the inguinofemoral vessels.

Internal Iliac nodal CTV: Superiorly begins at the bifurcation of the CI vessels with a uniform radial margin of 7mm excluding bone and muscle.

  • The contour discontinues when the vessels turn laterally, which occurs before they leave the pelvis.

Obturator nodal CTV: The strip of space about 15-18mm in diameter between the external and internal iliac nodal CTVs.

  • The superior aspect starting at the bifurcation of the internal and external iliac vessels.
  • Does not extend into bone, muscle or bladder. Inferior is when the obturator vessels leave the pelvis through the obturator foramen (lateral to the obturator internus muscle).

Regarding PTV expansions, the size of the expansion depends on multiple factors, including institutional standards.

  • Generally, the recommendation is to have a uniform expansion of 5-10mm around the nodal CTVs to create the nodal PTVs.

No consensus guidelines available for SBRT boost for non-operable, non-brachytherapy candidate early stage endometrial cancer. 

  • Kemmerer IJROBP 2013 is available as another reference.
  • In re-creating the brachytherapy dosage of the uterus, we defined the CTV as the entire uterus to a dose of 1500cGy in 6 fractions with an SIB to a contracted 5mm volume of the uterus.
    • Each CTV volume had a PTV expansion of 3mm.
    • Daily CBCTs were used.