From the Research
For 5-fraction stereotactic body radiation therapy (SBRT), the recommended dose constraint for the cauda equina is typically 30 Gy maximum point dose, with a volume constraint of less than 5 cc receiving 25 Gy. This constraint helps minimize the risk of radiation-induced injury to the nerve roots that could lead to neurological complications such as pain, sensory changes, or motor deficits. The cauda equina is considered a serial structure, meaning damage to even a small portion can result in significant clinical symptoms. These constraints are based on clinical experience and radiobiological considerations regarding the tolerance of neural tissues to high-dose radiation delivered in few fractions, as seen in studies such as 1. The relatively conservative dose limits reflect the critical nature of this structure and its limited repair capacity compared to other tissues. When planning SBRT treatments near the spine, careful contouring of the cauda equina and strict adherence to these dose constraints is essential to ensure safe treatment delivery. Some studies, such as 2, have demonstrated the safety of dose constraints for single fraction spine radiosurgery, but the specific dose constraints for 5-fraction SBRT are more closely aligned with the recommendations from more recent studies like 1. Key considerations in determining these dose constraints include:
- The risk of radiation-induced injury to the nerve roots
- The limited repair capacity of the cauda equina
- The importance of careful contouring and adherence to dose constraints in SBRT planning
- The need for ongoing evaluation and refinement of dose constraints based on emerging evidence, such as that presented in 3 and 4.