Fractionated radiation therapy in the treatment of stage III and IV cerebello-pontine angle neurinomas: preliminary results in 20 cases

Tomotherapy for neurofibromatosis Type 2: case report and review of the literature

Neurofibromatosis 2 (NF2) results in multiple central nervous system tumours. In this case report, the patient has one vestibular schwannoma, one trigeminal schwannoma and two meningiomas developed before the age of 30. Aiming to treat three targets at one fraction with minimal interaction and overlapping doses to normal tissue, the sophisticated equipment of tomotherapy was utilised for frameless stereotaxy; tomotherapy delivered intensity-modulated, rotational radiation therapy using a fan-beam delivery. Daily CT scans with the inbuilt CT scanner were also performed as part of the image-guided radiotherapy. The course of fractionated stereotactic radiotherapy consisted of eight fractions given three times per week with an overall treatment time of 17 days. For the meningioma over left parietal vertex, 4.5 Gy per fraction was given at 36 Gy/8 Fr/17 days. For the meningioma over anterior cerebral falx, 4 Gy per fraction was given at 32 Gy/8 Fr/17 days. For the two schwannomas as one target, 5 Gy per fraction was given at 40 Gy/8 Fr/17 days. The acute effect of the treatment was alopecia and mild headache. Subsequent follow-up confirmed clinical improvement. This is the first reported case of clinical experience with tomotherapy in the management of NF2.

Twenty years' experience in the treatment of acoustic neuromas with fractionated radiotherapy: a review of 45 cases

PURPOSE

To evaluate very long-term results of fractionated radiotherapy (FRT) of acoustic neuromas (AN).

METHODS AND MATERIALS

From January 1986 to January 2004, FRT was performed in 45 consecutive patients (46 AN). Indications were as follows: poor general condition contraindicating surgery, hearing preservation in bilateral neuromas, partial resection, nonsurgical recurrence. A 3-field to 5-field technique with static beams was used. A mean total dose of 51 Gy was given (1.80 Gy/fraction). The median tumor diameter was 31 mm (range, 11-55 mm). The median follow-up from FRT was 80 months (range, 4-227 months).

RESULTS

The particularity of our series consists of a very long-term follow-up of FRT given to selected patients. Nineteen patients died, two with progressive disease, and 17 from non-AN causes. A serviceable level of hearing was preserved in 7/9 hearing patients. No patient had facial or trigeminal neuropathy. Tumor shrinkage was observed in 27 (59%) and stable disease in 16 (35%). Tumor progression occurred in three patients, 12 to 15 months after FRT. Two additional tumors recurred after shrinkage 20 and 216 months after treatment and were operated on. Actuarial local tumor control rates at 5 and 15 years were 86%. For the patient who had a tumor recurrence at 216 months, histologic examination documented transformation to a low-grade malignant peripheral nerve sheath tumor.

CONCLUSION

Very long-term efficacy of FRT is well documented in this series. However, our results suggest that malignant transformation can occur many years after FRT so we advocate caution when using this treatment for young patients.

Long-term outcome of stereotactic radiosurgery (SRS) in patients with acoustic neuromas

PURPOSE

To evaluate the effectiveness and long-term outcome of stereotactic radiosurgery (SRS) for acoustic neuromas (AN).

PATIENTS AND METHODS

Between 1990 and 2001, we treated 26 patients with 27 AN with SRS. Two patients suffered from neurofibromatosis type 2. Before SRS, a subtotal or total resection had been performed in 3 and in 5 patients, respectively. For SRS, a median single dose of 13 Gy/80% isodose was applied.

RESULTS

The overall actuarial 5-year and 10-year tumor control probability in all patients was 91%. Two patients developed tumor progression after SRS at 36 and 48 months. Nineteen patients (73%) were at risk of treatment-related facial nerve toxicity; of these, 1 patient developed a complete facial nerve palsy after SRS (5%). A total of 93% of the lesions treated were at risk of radiation-induced trigeminal neuralgia. Two patients (8%) developed mild dysesthesia of the trigeminal nerve after SRS. The hearing preservation rate in patients with useful hearing before SRS was 55% at 9 years.

CONCLUSION

Stereotactic radiosurgery results in good local control rates of AN and the risk of cranial nerve toxicities is acceptable. As toxicity is lower with fractionated stereotactic radiotherapy, SRS should be reserved for smaller lesions.

Stereotactic Radiotherapy for Vestibular Schwannomas: Favorable Outcome with Minimal Toxicity

OBJECTIVE:

To determine the outcome and toxicity in patients with vestibular schwannomas treated with conventionally fractionated stereotactic radiotherapy (SRT) and to identify prognostic factors that are predictive of outcome.

METHODS:

Between 1992 and 2001, 70 patients with vestibular schwannomas were treated with linear accelerator-based SRT in our institutions. Eleven patients had neurofibromatosis Type II (NF2). The median age was 53 years (range, 17–82 yrs). The median tumor volume was 2.4 cm3 (range, 0.05–21.1 cm3). The indications for SRT were distributed as follows: 47% newly diagnosed, 31% progressive tumors after watchful waiting, 3% adjuvant postoperative radiation, and 19% recurrent tumors after surgical resection. The median dose was 54 Gy in 1.8 Gy per fraction, prescribed to 95% of the isodose line. Relocatable stereotactic frames were used for daily treatments. The median follow-up was 45.3 months.

RESULTS:

Tumor recurrence was defined as progressive enlargement of tumor on follow-up magnetic resonance imaging studies. One patient had a tumor recurrence at 38 months after SRT. The actuarial tumor control rates were 100 and 98% at 3 and 5 years, respectively. Three patients with a median tumor volume of 16.2 cm3 required surgical resection for persistent or increasing symptoms at a median of 37 months. The actuarial freedom from resection rates were 98 and 92% at 3 and 5 years, respectively. In multivariate analysis, tumor volume at time of treatment was predictive for neurosurgical intervention (surgical resection or shunt placement) after SRT (P = 0.001). The 3- and 5-year actuarial rates of freedom from any neurosurgical intervention were 100 and 97% for patients with tumor volume less than 8 cm3 and 74 and 47% respectively for patients with tumor of at least 8 cm3 (P < 0.0001). The 3-year actuarial rates of facial and trigeminal nerve preservation were 99 and 96%, respectively. Surgery before SRT was predictive of posttreatment trigeminal neuropathy. The 3-year actuarial rates of freedom from trigeminal neuropathy were 86 and 98% for patients with and without previous resection, respectively (P = 0.04). There was no difference in tumor control and cranial nerve function preservation rates seen in NF2 patients compared with non-NF2 patients. No second primary cancer or malignant transformation was observed.

CONCLUSION:

SRT in the conventionally fractionated approach results in a very favorable outcome with minimal toxicity, with results comparable to those of the best of the radiosurgery series. Patients with large tumors are more likely to undergo neurosurgical interventions after SRT. Patients who have undergone previous surgery are at increased risk of developing trigeminal neuropathy.

Update on conservative management of acoustic neuroma

OBJECTIVE

To update the authors' experience with conservative management of acoustic neuromas.

STUDY DESIGN

Retrospective chart review.

SETTING

Private practice and tertiary care referral setting.

INTERVENTION

Of 600 patients with acoustic neuroma, 102 were treated with the "wait and scan" treatment option. At least two magnetic resonance imaging scans were required of all patients.

MAIN OUTCOME MEASURES

Change in tumor size over time was evaluated, as were clinical symptoms: hearing status, tinnitus, balance disturbance, aural fullness, vertigo, headache, and facial pain, numbness, or weakness.

RESULTS

Of 102 patients, the average follow-up time interval was 28.5 months. Forty-five (44%) of 102 patients demonstrated a change in tumor size: an average total growth of 2.17 mm per year. In the remaining 54 patients (53%), no growth was demonstrated during a mean follow-up of 28.5 months. Three patients demonstrated actual tumor shrinkage. Of the 102 patients receiving conservative treatment, 85 (84%) reported hearing loss, 67 (66%) tinnitus, 37 (36%) balance disturbance, 29 (28%) aural fullness, 28 (27%) vertigo, 7 (7%) headache, 4 (4%) facial numbness, 2 (2%) facial weakness, and 0 (0%) facial pain.

CONCLUSION

Conservative management-"wait and scan"-for selected patients with acoustic neuroma is a reasonable choice of management instead of radiation or microsurgery. In some situations the individual morbidities associated with surgery or radiation make those treatments not in the patient's best interests. A third option is necessary in patients who cannot or do not wish to undergo those other treatments.

Stereotactic radiosurgery versus stereotactic radiotherapy for patients with vestibular schwannoma: a Leksell Gamma Knife Society 2000 debate

✓ By definition, the term “radiosurgery” refers to the delivery of a therapeutic radiation dose in a single fraction, not simply the use of stereotaxy. Multiple-fraction delivery is better termed “stereotactic radiotherapy.” There are compelling radiobiological principles supporting the biological superiority of single-fraction radiation for achieving an optimal therapeutic response for the slowly proliferating, late-responding, tissue of a schwannoma. It is axiomatic that complication avoidance requires precise three-dimensional conformality between treatment and tumor volumes. This degree of conformality can only be achieved through complex multiisocenter planning. Alternative radiosurgery devices are generally limited to delivering one to four isocenters in a single treatment session. Although they can reproduce dose plans similar in conformality to early gamma knife dose plans by using a similar number of isocenters, they cannot reproduce the conformality of modern gamma knife plans based on magnetic resonance image—targeted localization and five to 30 isocenters.

A disturbing trend is developing in which institutions without nongamma knife radiosurgery (GKS) centers are championing and/or shifting to hypofractionated stereotactic radiotherapy for vestibular schwannomas. This trend appears to be driven by a desire to reduce complication rates to compete with modern GKS results by using complex multiisocenter planning. Aggressive advertising and marketing from some of these centers even paradoxically suggests biological superiority of hypofractionation approaches over single-dose radiosurgery for vestibular schwannomas. At the same time these centers continue to use the term radiosurgery to describe their hypofractionated radiotherapy approach in an apparent effort to benefit from a GKS “halo effect.” It must be reemphasized that as neurosurgeons our primary duty is to achieve permanent tumor control for our patients and not to eliminate complications at the expense of potential late recurrence. The answer to minimizing complications while maintaining maximum tumor control is improved conformality of radiosurgery dose planning and not resorting to homeopathic radiosurgery doses or hypofractionation radiotherapy schemes.

Fractionated stereotactic radiotherapy for vestibular schwannoma (VS): comparison between cystic-type and solid-type VS

PURPOSE

To compare the effectiveness and complications of fractionated stereotactic radiotherapy (SRT) for cystic-type vestibular schwannoma (VS) with those of solid-type VS.

METHODS AND MATERIALS

In 65 patients treated with fractionated SRT between 1991 and 1999, 20 were diagnosed with cystic VS, in which at least one-third of the tumor volume was a cystic component on magnetic resonance imaging (MRI), and 45 were diagnosed with solid VS. Thirty-six Gy to 50 Gy in 20-25 fractions was administered to the isocenter and approximately 80% of the periphery of the tumor. All cystic and solid components were included in the gross tumor volume. The mean follow-up period was 37 months, ranging from 6 to 97 months.

RESULTS

The actuarial 3-year rate of no episode of enlargement greater than 2.0 mm was 55% for cystic-type and 75% for solid-type VS; the difference was statistically significant (p = 0.023). The actuarial 3-year tumor-reduction (reduction in tumor size greater than 2.0 mm) rates were 93% and 31%, respectively (p = 0.0006). The overall actuarial tumor control rate (no tumor growth greater than 2. 0 mm after 2 years or no requirement of salvage surgery) was 92% at 5 years in 44 patients with a follow-up period of 2 or more years. There was no difference in the class hearing preservation rate between cystic VS and solid VS. No permanent trigeminal or facial nerve palsy was observed in either group.

CONCLUSION

Transient tumor enlargement occurs in cystic VS more frequently than in solid-type VS, but the subsequent tumor-reduction rate in cystic VS is better.

Gamma surgery for vestibular schwannoma

OBJECT

The goal of this study was to assess the results of gamma surgery (GS) for vestibular schwannoma (VS) in 200 cases treated over the last 10 years and to review the role of this neurosurgical procedure in the management of VS.

METHODS

Follow-up reviews ranging from 1 to 10 years were available in 153 of these patients. Follow-up images in these cases were analyzed using computer software that we developed to obtain volume measurements for the tumors, and the clinical condition of the patients was assessed using questionnaires. Gamma surgery was the primary treatment modality in 96 cases and followed microsurgery in 57 cases. Tumors ranged in volume from 0.02 to 18.3 cm(3). In the group in which GS was the primary treatment, a decrease in volume was observed in 78 cases (81%), no change in 12 (12%), and an increase in volume in six cases (6%). The decrease was more than 75% in seven cases. In the group treated following microsurgery, a decrease in volume was observed in 37 cases (65%), no change in 14 (25%), and an increase in volume in six (11%). The decrease was more than 75% in eight cases. Five patients experienced trigeminal dysfunction; in three cases this was transient and in the other two it was persistent, although there has been improvement. Three patients had facial paresis (in one case this was transient, lasting 6 weeks; in one case there was 80% recovery at 18 months posttreatment; and in one case surgery was performed after the onset of facial paresis for presumed increase in tumor size). Over a 6-year period, hearing deteriorated in 60% of the patients. Three patients showed an improvement in hearing. No hearing deterioration was observed during the first 2 years of follow-up review.

CONCLUSIONS

Gamma surgery should be used to treat postoperative residual tumors as well as tumors in patients with medical conditions that preclude surgery. Microsurgery should be performed whenever a surgeon is confident of extirpating the tumor with a risk-benefit ratio superior to that presented in this study.

[Fractionated irradiation of cerebellopontine angle neurinoma: 12 years' experience of the Bordeaux University Hospital Center]

PURPOSE

To evaluate retrospectively the long-term results of fractionated radiation therapy (RT) in cerebello-pontine angle neurinomas (CPA).

METHODS AND MATERIAL

From January 1986 to October 1995, 29 patients with stage III and IV neurinomas were treated with external fractionated RT. One patient was irradiated on both sides and indications for RT were as follows: (1) general contraindications for surgery (16 patients); (2) hearing preservation in bilateral neurinomas after controlateral tumor exeresis (six patients); (3) partial tumor removal (five patients); and, (4) non-surgical recurrence (three patients). A three to four fields technique with coplanar static beams and conformal cerobend blocks was used; doses were calculated on a 95 to 98% isodoses and were given five days a week for a median total dose of 51 Gy (1.8 Gy/fraction). Most patients were irradiated with 6 to 10 MV photons).

RESULTS

Median follow-up was 66 months (seven to 120 months). Seven patients died, two with progressive disease, five from non-tumoral causes. Tumor shrinkage was observed in 13 patients (43.3%), stable disease in 14 (46.6%), and tumor progression in three. Two patients underwent total tumor removal after RT (one stable and one growing tumor). Hearing was preserved in four out of six patients. No patient experienced facial or trigeminal neuropathy.

CONCLUSION

Fractionated RT is a well tolerated and efficacious treatment of large non-surgical CPA neurinomas.

Comparison between observation policy and fractionated stereotactic radiotherapy (SRT) as an initial management for vestibular schwannoma

PURPOSE

To compare the use of an observation policy with that of stereotactic radiotherapy (SRT) for treatment of vestibular schwannoma.

METHODS AND MATERIALS

The study group consisted of 27 patients who underwent observation as an initial treatment (observation group) and 50 who received SRT (SRT group). The mean follow-up period was 35 months and 31 months, respectively. Stereotactic radiotherapy consisted of small-field fractionated radiotherapy (36-44 Gy in 20-22 fractions over 6 weeks) with or without a subsequent 4-Gy single irradiation boost.

RESULTS

Actuarial tumor control rate of the SRT group was significantly better than that of the observation group (p < 0.0001). The mean growth was 3.87 mm/year in the observation group and -0.75 mm/year in the SRT group (p < 0.0001). Eleven patients (41 %) in the observation group and 1 (2 %) in the SRT group received salvage therapy (p < 0.001). There was no difference in the actuarial Gardner and Robertson's class preservation curves for 5 years after the initial presentation.

CONCLUSION

Stereotactic radiotherapy using a fractionated schedule provides a better tumor control rate and a similar rate of deterioration for hearing levels compared to an observation policy. Initial SRT may be a reasonable alternative to a wait-and-see policy.

Audiological assessment before and after fractionated stereotactic irradiation for vestibular schwannoma

PURPOSE

To find the audiological outcome after LINAC-based fractionated stereotactic irradiation (STI).

MATERIALS AND METHODS

Twenty-four patients with vestibular schwannoma treated by fractionated STI between 1991 and 1997 had measurable hearing before STI and were followed audiologically for more than 6 months. The pure tone average (PTA) was measured by averaging the air-conduction threshold for five main frequencies (250-4000 Hz) before and periodically after STI in the 24 patients. Several possible prognostic factors for hearing preservation (defined as a PTA change at the last follow-up of less than 10 dB) were investigated. The median follow-up time was 22 months, ranging from 5 to 69 months. The irradiation schedule was 36 Gy in 20 fractions in 5 weeks to 44 Gy in 22 fractions in 6 weeks followed by 4 Gy/1 fraction boost.

RESULTS

The pure tone average before STI was distributed from 7 to 73 dB. Fifty percent of patients showed a change in PTA of less than 10 dB, 79.2% of patients showed a change in PTA of less than 20 dB and 20.8% of patients showed a change in PTA of more than 21 dB at the last follow-up. Only one patient (4%) became deaf. Cases with a sudden loss of hearing were more likely to experience hearing preservation than those with gradual loss of hearing (P<0.05). The mean age was younger in patients whose hearing was preserved (P<0.05). Poor pretreatment PTA appeared to linearly correspond to the changes in PTA (regression coefficient 0.78). The size of the tumor was not related to the change in PTA. No relationship was observed between the maximum or peripheral dose and the PTA change. The real benefit of stereotactic boost after small-field fractionated irradiation was not certain.

CONCLUSION

Fractionated STI produced a hearing preservation rate compatible with meticulously collimated multi-spots single fraction irradiation. Further follow-up is required to confirm the long-term benefits of fractionation.

Neck surgery in patients with primary oropharyngeal cancer treated by radiotherapy

BACKGROUND

The role of neck surgery in node-positive patients whose primary tumors are treated by definitive radiotherapy is controversial. This analysis was undertaken to assess the risk of withholding planned neck dissection in patients who obtain a complete nodal response to irradiation.

METHODS

We reviewed the records of 100 patients who presented between 1984 and 1993 with oropharyngeal cancers metastatic to the neck and whose primary tumors were treated by radiotherapy using the concomitant boost regimen. Seventy-five patients had their nodal disease treated definitively by radiotherapy; those who had complete clinical resolution of all nodal disease (62) had no planned surgery, while 13 underwent neck dissection for presumed residual disease. The remaining 25 patients had either node excision (8) or neck dissection (17) prior to radiotherapy.

RESULTS

There were 8 cases of isolated neck failure of which 3 occurred in the 62 patients who had no planned neck surgery, 0 in the 13 patients who had surgery for presumed residual (pathologically negative in 7). and 5 in the 25 patients who had initial neck surgery. In those who obtained a complete response to definitive radiotherapy, the risk of neck relapse was unrelated to pretreatment nodal size.

CONCLUSIONS

The policy of observation of the neck after complete nodal response to full-dose irradiation is both safe and cost effective. Imaging to confirm the resolution of nodal disease is recommended.

Fractionated stereotactic radiotherapy for the treatment of acoustic neuromas: preliminary results

PURPOSE

To evaluate the efficacy and toxicity of fractionated, stereotactic radiotherapy (SRT) for acoustic neuromas.

METHODS AND MATERIALS

Twelve patients with acoustic neuroma were treated with SRT between June 1992 and October 1994. Follow-up ranged from 16-44 months. Patient age ranged from 27-70 (median: 45). Eight patients were treated with primary SRT and four patients were treated after primary surgical intervention for recurrent [3] or persistent [1] disease. Tumor volumes were 1.2-18.4 cm3 (median: 10.1 cm3). Collimator sizes ranged from 30-50 mm (median: 37.5). Tumors received 1.8 Gy/day normalized to the 95% isodose line. Patients received a minimum prescribed dose of 54 Gy in 27-30 fractions over a 6-week period.

RESULTS

After a median follow-up of 26.5 months, local control was obtained in 12 out of 12 lesions. Tumor regression was noted in three patients, and tumor stabilization was found in the remaining nine patients. No patient developed a new cranial nerve deficit. One patients developed worsening of preexisting Vth cranial neuropathy and another experienced a decrease in hearing. However, all nine patients with useful hearing prior to SRT maintained useful hearing at last follow-up.

CONCLUSIONS

Stereotactic radiotherapy provided excellent local control without new cranial nerve deficits. These results must be viewed as tentative in nature because of the small number of patients and the short median follow-up period.

Fractionated radiation therapy in the treatment of stage III and IV cerebello-pontine angle neurinomas: long-term results in 24 cases

PURPOSE

To reevaluate long-term results of fractionated radiation therapy (RT) in a previously published series of cerebello-pontine angle neurinomas (CPA).

METHODS AND MATERIALS

From January 1986 to May 1992, 24 patients with Stage III and IV CPA neurinomas were treated with external fractionated RT; 7 patients had phacomatosis. One patient was irradiated on both sides and indications for radiotherapy were as follows: (a) poor general condition or old age contraindicating surgery, 14 cases; (b) hearing preservation in bilateral neurinomas after contralateral tumor removal, 5 cases; (c) partial resection or high risk of recurrence after subsequent surgery for relapse, 4 cases; (d) nonsurgical relapse, 2 cases. Most patients were irradiated with 9 MV photons. A three- to four-field technique with coned-down portals was used. Doses were calculated on a 95% isodose and were given 5 days a week for a mean total dose of 51 Gy (1.80 Gy/fraction).

RESULTS

Median follow-up from RT was 60 months (7 to 84); five patients died, two with progressive disease. Two patients underwent total tumor removal after RT (one stable and one growing tumor). On the whole, tumor shrinkage was observed in 9 patients (36%), stable disease in 13 (52%), and tumor progression in 3. Hearing was maintained in 3 out of 5 hearing patients with phacomatosis.

CONCLUSION

Fractionated RT appears to be an effective and well-tolerated treatment for Stage III and IV CPA neurinomas. Hearing can be preserved for a long time.

Stereotactic radiosurgery using the gamma knife for acoustic neuromas

PURPOSE

To assess the efficacy and toxicity of stereotactic radiosurgery using the gamma knife for acoustic neuromas.

METHODS AND MATERIALS

Between January 1990 and January 1993, 36 patients with acoustic neuromas were treated with stereotactic radiosurgery using the gamma knife. The median maximum tumor diameter was 21 mm (range: 6-32 mm). Tumor volumes encompassed within the prescribed isodose line varied from 266 to 8,667 mm3 (median: 3,135 mm3). Tumors < or = 20 mm in maximum diameter received a dose of 20 Gy to the margin, tumors between 21 and 30 mm received 18 Gy, and tumors > 30 mm received 16 Gy. The dose was prescribed to the 50% isodose line in 31 patients and to the 45%, 55%, 60%, 70%, and 80% isodose line in one patient each. The median number of isocenters per tumor was 5 (range: 1-12).

RESULTS

At a median follow-up of 16 months (range: 2.5-36 months), all patients were alive. Thirty-five patients had follow-up imaging studies. Nine tumors (26%) were smaller, and 26 tumors (74%) were unchanged. No tumor had progressed. The 1- and 2-year actuarial incidences of facial neuropathy were 52.2% and 66.5%, respectively. The 1- and 2-year actuarial incidences of trigeminal neuropathy were 33.7% and 58.9%, respectively. The 1- and 2-year actuarial incidence of facial or trigeminal neuropathy (or both) was 60.8% and 81.7%, respectively. Multivariate analysis revealed that the following were associated with the time of onset or worsening of facial weakness or trigeminal neuropathy: (a) patients < age 65 years, (b) dose to the tumor margin, (c) maximum tumor diameter > or = 21 mm, (d) use of the 18 mm collimator, and (e) use of > five isocenters. The 1- and 2-year actuarial rates of preservation of useful hearing (Gardner-Robertson class I or II) were 100% and 41.7% +/- 17.3, respectively.

CONCLUSION

Stereotactic radiosurgery using the gamma knife provides short-term control of acoustic neuromas when a dose of 16 to 20 Gy to the tumor margin is used. Preservation of useful hearing can be accomplished in a significant proportion of patients.

Linear accelerator-based stereotactic radiosurgery for acoustic schwannomas

PURPOSE

Stereotactic radiosurgery (SRS) is currently being investigated for treatment of acoustic schwannomas in patients who are not good surgical candidates. The vast majority of the available data is based on gamma knife-treated patients. We present the largest series of patients treated with linear accelerator-based SRS.

METHODS AND MATERIALS

Thirty-two patients with acoustic schwannomas were treated with SRS between July 1988 and February 1993; follow-up ranged from 4-59 months. Age ranged from 34-88 years (mean, 62 years). The primary presenting symptom was hearing loss in 30 patients and dementia in two patients. Indications for SRS were age > 65 years (17 patients); recurrence after surgery (13 patients); and medical infirmity (two patients). Dose to the periphery of the lesion ranged from 10-22.5 Gy (mean, 15.5 Gy) specified at the 68-90% isodose line (mean, 80%). Collimator size ranged from 12-35 mm (mean, 23 mm), indicating that the sizes of the tumors were significantly larger than those reported in most gamma knife series.

RESULTS

Follow-up magnetic resonance imaging (MRI) and/or computed tomography (CT) scans revealed the following at 1 year: tumor regression, 12 patients (63%); and no change, seven patients (37%). At 2 years, 11 tumors (73%) were smaller and four tumors (27%) were unchanged. At 3 years, seven patients (78%) had experienced tumor regression and two (22%) had no change. No patient experienced tumor progression after SRS. Seven patients (22%) suffered one or more treatment complications: new onset of 5th and/or 7th cranial nerve deficit (six patients), ataxia (two patients), and/or hydrocephalus necessitating VP shunt (two patients).

CONCLUSION

Linear accelerator-based SRS provides excellent short-term local control and a relatively low incidence of complications for acoustic schwannomas. Our data compare favorably with results obtained with gamma knife-based SRS. Additional follow-up will be necessary to evaluate the long-term results of treatment.