eContour

65 year old male with stage IVC salivary duct adenocarcinoma with a biopsy-proven solitary T7 spine metastasis treated with single fraction SBRT.

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Technique:

  • The patient was treated with stereotactic body radiation therapy (SBRT) using a single isocenter with 3 arc rotations.
  • Localization was performed using cone beam CT spine match ExacTrac positional monitoring.

Dose:

  • The high-dose PTV, which included gross metastatic disease, received 2400 cGy in 1 fraction.
  • The low-dose PTV, which included the elective osseous expansion, received 1800 cGy in 1 fraction.

Chemotherapy: This patient’s salivary duct adenocarcinoma was androgen receptor positive, therefore he was initiated on androgen deprivation therapy prior to radiation.

Sim/Planning:

  • Immobilization: BodyFix bag with arms up and immobilized by a Vac-loc bag.
  • Positioning: head first, supine.
  • CT scan without contrast.
  • MRI in treatment position, performed with and without contrast.
  • Motion management: None
  • Additional imaging: FDG PET with rigid registration.

 

Case contributed by Mayo Clinic Rochester

Contours per International Spine Radiosurgery Consortium consensus guidelines.

Target Volume Definitions

  • GTV: gross spinal metastatic disease contoured on CT bone window with guidance from the treatment position MRI and fused PET scan.
    • This case displays a sclerotic lesion, which is hypointense on T1 and T2 MR imaging and hyperintense on STIR imaging.
    • Lytic lesions are commonly hypointense on T1 and hyperintense on T2 imaging (Mugera J Magn Reson Imaging 2013).
  • CTV_low: elective osseous expansion per International Spine Radiosurgery Consortium consensus guidelines.
  • PTV_high*: GTV with 0-3 mm uniform expansion
  • PTV_low*: CTV_low with 0-3 mm uniform expansion
    *not all institutions use PTV expansions. With this approach, PTV_high = GTV and PTV_low = CTV_low (RTOG 0631).

OARs: Contour all OAR’s within 2 cm of the PTV_low.

  • Esophagus, heart, and great vessels are best visualized on soft tissue windows.
  • Lungs and the proximal bronchial tree are best visualized on the lung window.
  • MR imaging, particularly T2 images, is critical for contouring the cord.

A variety of dose and fraction schedules have been utilized in retrospective studies, single center prospective trials, and larger, cooperative group clinical trials. The most commonly utilized range of doses and fractionations are listed below. Selection of dose and fractionation may vary by metastatic location, size, tumor extent, and institutional practice patterns.

    • 16 to 24 Gy in 1 fraction to gross disease, 12-18 Gy to elective osseous volumes.
    • 24 Gy in 2 fractions to gross disease, 12-18 Gy to elective osseous volumes.
    • 27 to 36 Gy in 3 fractions to gross disease, 18-24 Gy to elective osseous volumes.
    • 30 to 50 Gy in 5 fractions to gross disease, 20-30 Gy to elective osseous volumes.

  • Use SINS scoring and other pre-treatment characteristics to determine the need for neurosurgery/orthopedic/interventional radiology consultation before radiation.

  • CT myelogram may be useful in cases where there is metal hardware artifact, making visualization of the disease and OARs difficult, or in cases where a patient is unable to undergo MR imaging.
    • The spinal cord is the most important OAR.
    • Consider use of a planning risk volume (PRV) such a 2mm uniform expansion around the cord, especially if advanced imaging is unavailable or cord position is uncertain.

  • Post-operative spine SBRT requires pre-operative and post-operative imaging with slight changes to contouring technique, but with similar commonly used doses and fractionations (Redmond J Neurosurg Spine 2017)

Dose Constraints: