Why are spinal cord constraints critical in radiotherapy planning?

• A. To prevent radiation-induced myelopathy and lasting neurological injury.
• B. To avoid hair loss.
• C. To shorten treatment time.
• D. To increase dose uniformity.

Answer: (A)

Protecting neurologic function is the priority when planning radiotherapy because the spinal cord has a limited tolerance to radiation and damage can be permanent. Radiation-induced myelopathy, though relatively rare, is a serious late complication that can emerge months to years after treatment and may progress despite therapy stopping. To prevent this, planners impose tight dose constraints on the spinal cord, aiming to keep the maximum dose and the dose to critical volumes below thresholds that are associated with unacceptable risk. The way dose is delivered—fraction size and total amount—affects this risk, so constraints are evaluated within a fractionated framework and through dose–volume analysis to ensure the cord is spared while the tumor still receives an effective dose. While other planning concerns like hair loss, overall treatment time, or achieving uniform dose distribution are important, they do not address the high-stakes risk of irreversible spinal cord injury as directly as maintaining strict cord constraints does.