How do you contour the cauda equina for a lumbar spine SBRT case below the spinal cord?

I typically contour the cauda equina at the level of the upper lumbar spine just below the spinal cord based on T2-weighted MRI and utilize a 2 mm PRV. If the entire spinal canal is instead contoured just below the cord, this may lead to underdosing of the posterior aspect of the vertebral body.

At t...

I typically use a 1 mm PRV for cauda and 0 mm/no PRV for lumbosacral plexus.

There are a variety of constraints you can use.

Robert Timmerman, PMID 34919882

• 1-Fraction
  • Cauda: D0.03cc < 16 Gy; D5cc < 14 Gy
  • Sacral Plexus: D0.03cc < 16 Gy; D5cc <14.4 Gy
• 3-Fraction
  • Cauda: D0.03cc < 25.5 Gy; D5cc < 21....