Radiation Dose Rate, Biologically Effective Dose, and Tumor Characteristics on Local Control and Toxicity After Radiosurgery for Acoustic Neuromas

World Neurosurg. 2021 Aug:152:e512-e522. doi: 10.1016/j.wneu.2021.05.122. Epub 2021 Jun 16.


Objective: To evaluate the relationships between calibration dose rate, calculated biologically effective dose (BED), and clinical factors and tumor control after stereotactic radiosurgery (SRS) for acoustic neuroma.

Methods: We performed a retrospective study of all patients with acoustic neuromas treated with frame-based cobalt-60 SRS at a single institution between 2005 and 2019. The calibration dose rate and cobalt-60 half-life were used to calculate the nominal dose rate during treatment. An SRS-specific monoexponential model accounting for treatment time per lesion was used to estimate BED.

Results: The study included 607 patients with 612 acoustic neuromas. Median follow-up was 5.0 years. There was no association between dose rate or BED with local failure (LF), radiologic edema, or symptomatic edema. Cystic tumors (adjusted hazard ratio 0.26, P = 0.028) were associated with lower LF, while use of SRS as salvage treatment for growing tumors (adjusted hazard ratio 4.9, P < 0.0001) was associated with higher LF. LF occurred more frequently in larger-diameter tumors, while radiologic or symptomatic edema occurred more frequently in larger-volume tumors.

Conclusions: Radiosurgery dose rate and BED were not associated with tumor control or radiologic or symptomatic edema. Salvage SRS and larger tumors were associated with a higher LF rate, while cystic tumors were associated with a lower LF rate. Patients with larger tumors should be counseled appropriately about potential side effects and when to seek follow-up care.

Keywords: Acoustic neuroma; Brain edema; Cysts; Radiobiology; Radiosurgery; Vestibular schwannoma.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Calibration
  • Cobalt Radioisotopes
  • Cranial Nerve Neoplasms / diagnostic imaging
  • Cranial Nerve Neoplasms / radiotherapy*
  • Cysts / radiotherapy
  • Dose-Response Relationship, Radiation
  • Edema / etiology
  • Female
  • Half-Life
  • Humans
  • Magnetic Resonance Imaging
  • Male
  • Middle Aged
  • Neuroma, Acoustic / diagnostic imaging
  • Neuroma, Acoustic / radiotherapy*
  • Postoperative Complications / epidemiology
  • Radiation Dosage*
  • Radiosurgery / adverse effects*
  • Radiosurgery / methods*
  • Retrospective Studies
  • Treatment Outcome
  • Tumor Burden
  • Young Adult


  • Cobalt Radioisotopes