Acoustic neuroma medical therapy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]

Overview

The predominant therapy for acoustic neuroma is surgical resection. Adjunctive radiation and radiosurgery may be required. Since acoustic neuromas tend to be slow-growing and are benign tumors, careful observation over a period of time may be appropriate for some patients.[1]

Medical Therapy

Medical therapy for acoustic neuroma includes radiation therapy. Factors that affect the selection of the right treatment include:

  • Size of the tumor
  • Tumor growth
Tumor Size Treatment line Treatment
Tumor < 1 to 1.5 cm
No tumor growth First Observation
Second Focused radiation or surgery
With tumor growth First Focused radiation or surgery
Adjunct Salvage radiation or surgery
Second Observation
Tumor 1.5 to 3cm
No tumor growth First Focused radiation or surgery
Adjunct Salvage radiation or surgery
Second Observation
With tumor growth First Focused radiation or surgery
Adjunct Salvage radiation or surgery
Second Observation
Tumor > 3cm
First Surgery
Second Observation

Observation

Since acoustic neuromas tend to be slow-growing and are benign tumors, careful observation over a period of time may be appropriate for some patients.The patient is observed for facial nerve function, hearing, tinnitus and ataxia. An MRI is performed every 6 months or yearly depending on the rate of tumor growth. The average growth rate of tumor is 1.15 to 2.4 mm per year. If the tumor grows or causes serious symptoms, treatment is suggested. If the scans show the tumor is growing or if the tumor causes progressive symptoms or other difficulties, you may need to undergo treatment. Observation is recommended in the following patients:[1]

  • Patients with a tumor in their only hearing or better hearing ear
  • When the tumor is of a size that hearing preservation with treatment would be unlikely
  • Elderly patients
  • Small tumors in older individuals that do not grow
  • Patients with small tumors with good hearing
  • Patients with medical conditions that increase the risk of surgery
  • Patients who refuse treatment
  • Patients with a tumor on the side of an only hearing ear or only seeing eye

Radiation Therapy

Another treatment option for an acoustic neuroma is radiation. Radiation therapy approaches that have been used in patients with acoustic neuroma include:[1]

Stereotactic radiotherapy

The multi-dose treatment, FSR, delivers smaller doses of radiation over a period of time, requiring the patient to return to the treatment location on a daily basis, from 3 to 30 times, generally over several weeks. Each visit lasts a few minutes and most patients are free to go about their daily business before and after each treatment session. Early data indicates that FSR may result in better hearing preservation when compared to single-session SRS.

Proton beam therapy

  • The use of proton beam therapy permits the delivery of high doses of radiotherapy to the target volume while limiting the dose received by surrounding tissues. It provides maximum local tumor control with minimum cranial nerve injuries.
  • Follow-up after SRS and FSR typically involves an MRI scan and audiogram at six months, one year, then yearly for several years, then every second or third year indefinitely to make sure the tumor does not start to grow again. All types of radiation therapy for acoustic neuromas may result in "tumor control" in which the tumor cells die and necrosis occurs. Tumor control means that the tumor growth may slow or stop and, in some cases, the tumor may shrink in size. These techniques are performed in the outpatient setting, not requiring general anesthesia or a hospital stay. The purpose of these techniques is to arrest the growth of the tumor causing the tumor to die, which is called necrosis. This treatment has not been well studied and thus it is unclear if it is better than observation or surgery. Tumors under 2.5 - 3.0 cm, without significant involvement of the brainstem, are more favorable for radiation treatment. Side effects can occur when the brainstem is irradiated and in some cases of large tumors, radiation is contraindicated. Studies are beginning to appear for the other modalities. All of the techniques use computers to create three dimensional models of the tumor and surrounding neural structures. Radiation physicists then create dosimetry maps showing the level of radiation to be received by the tumor and the normal tissues. Surgeons, radiation therapists and physicists then modify the dosimetry to maximize tumor doses and minimize radiation toxicity to surrounding normal tissues. The head is stabilized with a metal frame pinned to the head (Gamma Knife) or a fitted mask shield (CyberKnife, linear accelerator, fractionated XRT). Treatments generally last 30–60 minutes. Just like for surgery, the experience of the team in treating acoustic neuromas with all modalities (surgery and radiation) can affect outcomes. There are a multitude of studies supporting short-term (<5 yrs.) and longer-term (over 10 yrs.) tumor control with radiation. Unfortunately, as is the case with microsurgical studies, most have inconsistent follow-up to draw definitive conclusions.
  • Several types of machines deliver focused radiation treatment suitable for treating acoustic neuromas. The underlying premise is to treat the tumor with a high dose of radiation while sparing the nerves and brain tissues. Much of the long term data comes from the Gamma Knife literature since this was one of the earliest techniques used to radiate acoustic neuromas on a large scale. The machines suitable for treating acoustic neuroma include:
  • Gamma Knife
    • The Gamma Knife uses 195-201 fixed cobalt-60 radiation sources that are "collimated" to intersect at the site of the tumor and is a single dose treatment. In this way, each individual beam of radiation has very little effect, but where they all intersect produces a maximum effect on the tumor. Very similar results can be obtained using a linear accelerator (LINAC) as the radiation source, such as with the Novalis or CyberKnife with multi-dose treatment.
  • Linear accelerator (LINAC)
  • CyberKnife
  • Novalis
  • Trilogy

Advantages of radiation therapy

  • Decreased length of stay

Disadvantages of radiation therapy

  • In almost no cases have acoustic neuroma tumors been completely eliminated by radiation treatments. Radiation does not remove the tumor like microsurgery can.
  • Radiotherapy patients require lifetime follow-up with MRI scans.
  • Rare reports of malignant degeneration (a benign tumor becoming malignant) after radiotherapy have been found.
  • In some cases the tumor does not die and continues to grow. In those instances, another treatment is necessary - either microsurgery or sometimes another dose of radiation.
  • Higher incidence of trigeminal nerve injury.
  • Unknown incidence of secondary malignancies.
  • Long-term balance dysfunction.

References

  1. 1.0 1.1 1.2 Vestibular Schwannoma. Wikipedia(2015) https://en.wikipedia.org/wiki/Vestibular_schwannoma Accessed on October 2 2015

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