Is bilateral conventional radiotherapy with 50.4 Gy (Gray) in 28 fractions a suitable treatment option for simultaneously addressing both vestibular schwannomas?

Bilateral Conventional Radiotherapy for Vestibular Schwannomas

Bilateral conventional radiotherapy with 50.4 Gy in 28 fractions is not recommended for simultaneously treating both vestibular schwannomas, as stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (SRT) with more focused delivery and lower total doses is the preferred radiation approach for these tumors. 1, 2

Radiation Treatment Options for Vestibular Schwannomas

Preferred Radiation Approaches

• Stereotactic Radiosurgery (SRS): Single-fraction delivery of 11-14 Gy is the standard for small to medium-sized vestibular schwannomas 1
• Fractionated Stereotactic Radiotherapy (SRT): For larger tumors, hypofractionated SRT using up to 10 fractions is increasingly used 1

Key Considerations

• The proposed conventional radiotherapy dose of 50.4 Gy in 28 fractions is significantly higher than the recommended doses for vestibular schwannomas
• This higher dose and less conformal delivery may increase risk of damage to:
  • Facial nerve (CN VII)
  • Cochlear nerve (CN VIII)
  • Brainstem
  • Adjacent cranial nerves

Evidence-Based Recommendations

The European Association of Neuro-Oncology (EANO) guidelines specifically state that for larger tumors, fractionation is mandatory, but recommend fractionated radiotherapy or hypofractionated SRT using up to 10 fractions 1. There is no mention of conventional radiotherapy with doses as high as 50.4 Gy.

The Congress of Neurological Surgeons guidelines note that there is no difference in radiographic control and clinical outcomes using single or multiple fractions, but do not recommend conventional fractionation schemes 1.

Treatment Algorithm for Bilateral Vestibular Schwannomas

1. For small tumors (<3 cm without mass effect):

   • SRS with 11-14 Gy in a single fraction 1

2. For larger tumors or those with mass effect:

   • Hypofractionated SRT with up to 10 fractions 1
   • Consider surgical resection for tumors causing significant brainstem compression 2

3. For bilateral tumors (as in NF2):

   • Staged approach addressing one tumor at a time 2
   • SRS for medium-sized tumors
   • Consider bevacizumab for NF2-associated tumors (evidence class II, recommendation level B) 1, 2

Common Pitfalls to Avoid

• Excessive radiation dose: The proposed 50.4 Gy is much higher than the 11-14 Gy typically used in SRS, potentially increasing toxicity 1
• Inadequate conformality: Conventional radiotherapy lacks the precision of SRS/SRT, increasing risk to adjacent critical structures 1, 2
• Simultaneous treatment of bilateral tumors: A staged approach is generally preferred to minimize risk of bilateral cranial nerve damage 2

Conclusion

For bilateral vestibular schwannomas, the evidence strongly supports using either SRS (for smaller tumors) or hypofractionated SRT (for larger tumors) rather than conventional radiotherapy with 50.4 Gy in 28 fractions. This approach optimizes tumor control while minimizing risk to critical structures, particularly the facial and cochlear nerves.