Radiation therapy, in its various forms, has been applied to the treatment of acoustic neuromas. Historically this was done since the results of surgery in the past (prior to the 1970’s) were actually quite dismal in most cases. However, with improvements in microsurgical technique and surgical approach, as well as, the acquisition of great experience by surgical teams such as at the House Clinic, very few patients overall have undergone any form of radiation therapy for their acoustic neuroma. Since acoustic neuromas are benign growths we do not routinely advise radiation treatment. Radiation therapy is not risk free and does not result in disappearance of the tumor. Hearing loss, facial paralysis, and other serious complications have also occurred after radiation therapy. After this treatment, some patients have experienced continued tumor growth and have required surgical removal, which is much more difficult due to the effects of the radiation. High complication rates and especially treatment failures have been a particular characteristic of treatment with conventional and focused beam radiotherapy techniques. In recent years, patients have been treated with a different method of radiotherapy which is called stereotactic radiosurgery.
Stereotactic radiosurgery is a method of delivering a radiation dose in such a way as to minimize the affects of the radiation on the surrounding normal tissues while delivering a very high dose to the tumor. Low dose radiation beams are aimed from many different directions to converge on the tumor and, thereby, deliver a very high radiation dose. This type of treatment comes in several different forms. These methods are variously named the gamma-knife, LINAC, proton beam therapy, and fractionated radiosurgery. There are many questions that are not answered in terms of the long-term result of this therapy. These procedures are attractive to many patients because of the short-term promise of low complication rates and a shorter hospital stay. This form of treatment is an option only for patients with tumors measuring less than 3cm in diameter, as radiosurgery is ineffective in larger tumors.
A published series of patients treated by stereotactic radiosurgery have documented the various complications that can occur with this treatment. This includes facial paralysis, facial numbness, hearing loss, damage to the brain stem, hydrocephalus, and dizziness. Because of the high complication rates with early attempts at stereotactic radiosurgery, the various centers performing this treatment have continuously been decreasing the radiation dose delivered in these cases. This creates a very real concern for the long-term effectiveness of this therapy. It is well demonstrated that decreasing radiation doses leads to a lowering of the effectiveness of radiation treatments in both malignant and benign tumors. The question of long-term efficacy will not be answered for several more years when patients who have recently undergone this treatment are continually followed and studied for any recurrence of the tumor. These patients will need yearly MRI scans for many years to monitor the tumors for further growth. For the time being, this form of therapy has to remain classified as “experimental” because of the continuous alterations that are ongoing in radiation dose and the uncertain long-term effectiveness of the treatment.
Currently, most patients who are referred for stereotactic radiosurgery are elderly or are in poor general medical condition, making them a high surgical risk in terms of undergoing general anesthesia. The size of tumor is also extremely important in terms of someone’s candidacy for this treatment. Tumors which are 3cm or larger in diameter are not candidates for stereotactic radiosurgery as it has been shown to be completely ineffective in these large tumors.