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

Outcome after Radiotherapy for Vestibular Schwannomas (VS)—Differences in Tumor Control, Symptoms and Quality of Life after Radiotherapy with Photon versus Proton Therapy

Background: To evaluate differences in local tumor control (LC), symptoms and quality of life (QOL) of 261 patients with VS after stereotactic radiosurgery/hypofractionated stereotactic radiotherapy (SRS/HFSRT) vs. fractionated radiotherapy (FRT) vs. fractionated proton therapy (FPT) were studied. Methods: For SRS/HFSRT (n = 149), the median fraction dose applied was 12 Gy. For FRT (n = 87) and FPT (n = 25), the median cumulative doses applied were 57.6 Gy and 54 Gy (RBE), respectively. FRT and FPT used single median doses of 1.8 Gy/Gy (RBE). Median follow-up was 38 months. We investigated dosimetry for organs at risk and analyzed toxicity and QOL by sending out a questionnaire. Results: LC was 99.5% at 12 months after RT with no statistical difference between treatment groups (p = 0.19). LC was significantly lower in NF2 patients (p = 0.004) and in patients with higher tumor extension grade (p = 0.039). The hearing preservation rate was 97% at 12 months after RT with no statistical difference between treatment groups (p = 0.31). Facial and trigeminal nerve affection after RT occurred as mild symptoms with highest toxicity rate in FPT patients. Conclusion: SRS/HFSRT, FRT and FPT for VS show similar overall clinical and functional outcomes. Cranial nerve impairment rates vary, potentially due to selection bias with larger VS in the FRT and FPT group.

Hearing preservation following fractionated stereotactic radiotherapy for vestibular schwannomas: prognostic implications of cochlear dose

Object

The goal in this study was to evaluate hearing preservation rates and to determine prognostic factors for this outcome following fractionated stereotactic radiotherapy (FSRT) of vestibular schwannoma.

Methods

Thirty-four consecutive patients with serviceable hearing who received FSRT between May 1998 and December 2003 were identified. Clinical and audiometry data were collected prospectively. The prescription dose was 45 Gy in 25 fractions prescribed to the 90% isodose line. The median follow-up duration was 36.5 months (range 12–85 months). The actuarial 2- and 4-year local control rates were 100 and 95.7%, respectively. Permanent trigeminal and facial nerve complications were 0 and 6%, respectively. The actuarial 2- and 3-year serviceable hearing preservation rates were both 63%. The median loss in speech reception threshold was 15 dB (range −10 to 65 dB). The radiotherapy dose to the cochlea was the only significant prognostic factor for hearing deterioration. Radiotherapy dose to the cochlear nucleus, patient age, sex, pre-FSRT hearing grade, tumor volume, and intracanalicular tumor volume failed to show any significance as prognostic factors.

Results

Five cases were replanned with four different radiotherapy techniques (namely arcs, dynamic arcs, static conformal fields, and intensity-modulated radiotherapy), with the cochlea defined as an organ at risk. In all cases, replanning resulted in statistically significant reduction in radiation to the cochlea (p = 0.001); however, no single replanning technique was found to be superior.

Conclusions

The radiation dose to the cochlea is strongly predictive for subsequent hearing deterioration. It is essential for the cochlea to be outlined as an organ at risk, and for radiation techniques to be optimized, to improve long-term hearing preservation.

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.

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.

Results of outpatient gamma knife radiosurgery for primary therapy of acoustic neuromas

Stereotactic radiosurgery (SRS) has been recognized as a non-invasive alternative to surgery for the treatment of acoustic neuromas. Purpose of the current study was to define the impact of outpatient gamma knife radiosurgery (GKS) for patients with unilateral sporadic acoustic neuromas treated within ten years. Follow-up images were analyzed using tumor volume measurements. 219 patients with sporadic acoustic neuromas were treated by GKS as primary therapy. Patients with NF-2 tumors were excluded. Patients were eligible for GKS up to a size limit of 12.5 cm3. The median follow up time was 6 years after radiosurgery. The local tumor control rate was high (97%). Cranial nerve morbidities were comparably low. 10% of the patients developed hearing loss after radiosurgery and one patient experienced a transient facial neuropathy (0.5%). Transient trigeminal neuropathy developed in 12 patients (5%) and was found to be dependent on the tumor size before treatment. Outpatient gamma knife radiosurgery is a safe and effective treatment method for selected patients with sporadic vestibular schwannomas.

Management of acoustic schwannoma

PURPOSE

To discuss the optimal management for patients with acoustic schwannoma.

MATERIALS AND METHODS

Review of the pertinent literature.

RESULTS

Microsurgery, stereotactic radiosurgery, and fractionated radiotherapy result in cure rates that approximate 90% at 5 years. Depending on tumor extent and surgical approach, the morbidity of microsurgery may exceed that of stereotactic radiosurgery and fractionated radiotherapy. Patients with useful hearing before treatment may have a higher likelihood of hearing preservation after radiotherapy compared with radiosurgery.

CONCLUSION

Both microsurgery and radiosurgery are good options for patients with tumors less than 3 cm. Depending on tumor extent and the surgical approach, the morbidity of microsurgery may exceed that of radiosurgery. Patients with useful hearing may have a higher likelihood of hearing preservation after radiotherapy. Microsurgery is preferred for patients in whom the disease progresses after initial irradiation and in patients with tumors larger than 3 cm.

Management of vestibular schwannoma by fractionated stereotactic radiotherapy and associated cerebrospinal fluid malabsorption

OBJECT

The goal of this study was to investigate outcomes in patients with vestibular schwannoma (VS) who were treated with fractionated stereotactic radiotherapy (SRT).

METHODS

One hundred one patients with VS were treated with fractionated SRT at a radiation level of 40 to 50 Gy administered in 20 to 25 fractions over a 5- to 6-week period. The median tumor size in these patients was 19 mm (range 3-40 mm), and 27 tumors were larger than 25 mm. Patients were consistently followed up using magnetic resonance imaging every 6 months for 5 years in principle. The median follow-up period was 45 months. The actuarial 5-year rate of tumor control (no growth > 2 mm and no requirement for salvage surgery) was 91.4% (95% confidence interval 85.2-97.6%). Three patients with progressive tumors underwent salvage tumor resection. The actuarial 5-year rate of useful hearing preservation (Gardner-Robertson Class I or II) was 71%. The observed complications of fractionated SRT included transient facial nerve palsy (4% of patients), trigeminal neuropathy (14% of patients), and balance disturbance (17% of patients). No new permanent facial weakness occurred after fractionated SRT. Eleven patients (11%) who had progressive communicating hydrocephalus (cerebrospinal fluid malabsorption) and no evidence of tumor growth after fractionated SRT required a shunt. The symptoms of this type of hydrocephalus were similar to those of normal-pressure hydrocephalus and occurred 4 to 20 months (median 12 months) after fractionated SRT. The mean size (+/- standard deviation) of tumors causing symptomatic hydrocephalus (25.5 +/- 7.8 mm) was significantly larger than that of other tumors (18.2 +/- 8.7 mm) (p = 0.011). Only four of the 72 patients with tumors smaller than 25 mm in maximum diameter received a shunt.

CONCLUSIONS

Fractionated SRT resulted in an excellent tumor control rate, even for relatively large tumors, and produced a high rate of hearing preservation that was comparable to the best results of single-fraction radiosurgery. The progression of communicating hydrocephalus should be monitored closely, particularly in patients harboring a large VS.

Proton beam radiosurgery for vestibular schwannoma: tumor control and cranial nerve toxicity

OBJECTIVE

We sought to determine the tumor control rate and cranial nerve function outcomes in patients with vestibular schwannomas who were treated with proton beam stereotactic radiosurgery.

METHODS

Between November 1992 and August 2000, 88 patients with vestibular schwannomas were treated at the Harvard Cyclotron Laboratory with proton beam stereotactic radiosurgery in which two to four convergent fixed beams of 160-MeV protons were applied. The median transverse diameter was 16 mm (range, 2.5-35 mm), and the median tumor volume was 1.4 cm(3) (range, 0.1-15.9 cm(3)). Surgical resection had been performed previously in 15 patients (17%). Facial nerve function (House-Brackmann Grade 1) and trigeminal nerve function were normal in 79 patients (89.8%). Eight patients (9%) had good or excellent hearing (Gardner-Robertson [GR] Grade 1), and 13 patients (15%) had serviceable hearing (GR Grade 2). A median dose of 12 cobalt Gray equivalents (range, 10-18 cobalt Gray equivalents) was prescribed to the 70 to 108% isodose lines (median, 70%). The median follow-up period was 38.7 months (range, 12-102.6 mo).

RESULTS

The actuarial 2- and 5-year tumor control rates were 95.3% (95% confidence interval [CI], 90.9-99.9%) and 93.6% (95% CI, 88.3-99.3%). Salvage radiosurgery was performed in one patient 32.5 months after treatment, and a craniotomy was required 19.1 months after treatment in another patient with hemorrhage in the vicinity of a stable tumor. Three patients (3.4%) underwent shunting for hydrocephalus, and a subsequent partial resection was performed in one of these patients. The actuarial 5-year cumulative radiological reduction rate was 94.7% (95% CI, 81.2-98.3%). Of the 21 patients (24%) with functional hearing (GR Grade 1 or 2), 7 (33.3%) retained serviceable hearing ability (GR Grade 2). Actuarial 5-year normal facial and trigeminal nerve function preservation rates were 91.1% (95% CI, 85-97.6%) and 89.4% (95% CI, 82-96.7%). Univariate analysis revealed that prescribed dose (P = 0.005), maximum dose (P = 0.006), and the inhomogeneity coefficient (P = 0.03) were associated with a significant risk of long-term facial neuropathy. No other cranial nerve deficits or cancer relapses were observed.

CONCLUSION

Proton beam stereotactic radiosurgery has been shown to be an effective means of tumor control. A high radiological response rate was observed. Excellent facial and trigeminal nerve function preservation rates were achieved. A reduced prescribed dose is associated with a significant decrease in facial neuropathy.

Linear accelerator–based radiosurgery for vestibular schwannoma

Despite major advances in skull base surgery and microsurgical techniques, surgery for vestibular schwannoma (VS) carries a risk of complications. Some are inherent to general anesthesia and surgery of any type and include myocardial infarction, pneumonia, pulmonary embolism, and infection. Some are specific to neurosurgery in this area of the brain, and include hydrocephalus, cerebrospinal fluid leak, facial nerve paralysis, facial numbness, hearing loss, ataxia, dysphagia, and major stroke. Even in the hands of very experienced acoustic surgeons, these risks cannot be eliminated.

Radiosurgery provides an outpatient, noninvasive alternative for the treatment of small acoustic schwannomas. Initially radiosurgery was undertaken in “high-risk” patients, including the elderly, those with severe medical comorbidities, and those in whom tumors recurred after surgery. Additionally, a high rate of cranial nerve morbidity was reported. With improvements in dosimetry planning and dose selection, however, authors practicing at radiosurgical centers now report very low complication rates, as well as high tumor control rates.

In this report the authors specifically review the results of linear accelerator–based radiosurgery for VS and compare these outcomes with the best surgical alternatives.

Fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT) for small acoustic neuromas

Eight patients with acoustic neuromas were treated using a novel method developed at our institution for delivering fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT). We present treatment parameters, dosimetry analysis, and preliminary clinical outcome. The method incorporates high-precision invasive fixation, obliquely-oriented tomotherapy arcs, and reduced dimension pencil beams. The delivered dose distributions for the 8 patients treated from April 1999 to May 2001 were assessed for dose conformality, homogeneity, and doses to organs at risk. Total doses prescribed were 54 Gy in daily doses of 1.8 Gy. Results show that the median planning target volume (gross tumor volume plus a safety margin of 2 mm) was 2.48 cm3 (1.64 to 16.86 cm3) and that the median conformality and homogeneity indices were 1.69 (1.56 to 2.16) and 1.12 (1.09 to 1.19), respectively. The respective average mean and maximum doses to the brain stem were 12.67 Gy and 53.86 Gy. The treatment parameters for the novel FS-IMRT method developed here document excellent dose conformality and normal tissue sparing. Preliminary short-term follow-up (mean 17, median 18.5 months) revealed a 100% local control and hearing preservation rate. No new persistent impairment of facial and trigeminal nerve was observed. Our current follow-up experience indicates a reasonable potential for achieving outcomes comparable to established stereotactic radiotherapy techniques.

Fractionated stereotactic radiotherapy for the treatment of vestibular schwannomas: combined experience of the Toronto-Sunnybrook Regional Cancer Centre and the Princess Margaret Hospital

PURPOSE

To evaluate the efficacy and toxicity of fractionated stereotactic radiotherapy (FSRT) for vestibular schwannomas in patients treated at two university-affiliated hospitals.

METHODS AND MATERIALS

Thirty-nine patients were treated between April 1996 and September 2000. The median age was 56 years (range: 29-80), and median maximal tumor diameter was 20 mm (range: 9-40). A total of 11 patients had fifth and/or seventh cranial nerve dysfunction before irradiation; 2 patients had only facial weakness, 5 patients had only facial numbness, and 4 patients had both facial weakness and numbness. Thirty-three patients were treated with primary FSRT, and 6 patients were treated for recurrent or persistent disease after previous surgery. All patients were treated with 6-MV photons using a stereotactic system with a relocatable frame. The 39 patients received 50 Gy in 25 fractions over 5 weeks. Median follow-up was 21.8 months (range: 4.4-49.6).

RESULTS

Local control was achieved in 37 patients (95%). Two patients experienced deterioration of their symptoms at 3 and 20 months as a result of clinical progression in one case and tumor progression in the other and underwent surgery post FSRT. A total of 19/28 (67.9%) patients preserved serviceable hearing after FSRT. Deterioration of the facial and trigeminal nerves was observed in only 2 patients who were treated with surgery post FSRT.

CONCLUSION

FSRT provided excellent tumor control with minimal morbidity and good hearing preservation in this cohort of patients. Longer follow-up is required to confirm long-term control rates.

Radiotherapy and radiosurgery for skull base tumors

Tumors arising in the vicinity of the skull base are relatively uncommon; however, lesions that may be successfully treated by radiotherapy and radiosurgery include temporal bone chemodectomas, schwannomas, juvenile angiofibromas, pituitary adenomas, and meningiomas. This article reviews treatment techniques and results and discusses the pertinent literature.

Analysis of risk factors associated with radiosurgery for vestibular schwannoma

OBJECT

The aim of this study was to identify factors associated with delayed cranial neuropathy following radiosurgery for vestibular schwannoma (VS or acoustic neuroma) and to determine how such factors may be manipulated to minimize the incidence of radiosurgical complications while maintaining high rates of tumor control.

METHODS

From July 1988 to June 1998, 149 cases of VS were treated using linear accelerator radiosurgery at the University of Florida. In each of these cases, the patient's tumor and brainstem were contoured in 1-mm slices on the original radiosurgical targeting images. Resulting tumor and brainstem volumes were coupled with the original radiosurgery plans to generate dose-volume histograms. Various tumor dimensions were also measured to estimate the length of cranial nerve that would be irradiated. Patient follow-up data, including evidence of cranial neuropathy and radiographic tumor control, were obtained from a prospectively maintained, computerized database. The authors performed statistical analyses to compare the incidence of posttreatment cranial neuropathies or tumor growth between patient strata defined by risk factors of interest. One hundred thirty-nine of the 149 patients were included in the analysis of complications. The median duration of clinical follow up for this group was 36 months (range 18-94 months). The tumor control analysis included 133 patients. The median duration of radiological follow up in this group was 34 months (range 6-94 months). The overall 2-year actuarial incidences of facial and trigeminal neuropathies were 11.8% and 9.5%, respectively. In 41 patients treated before 1994, the incidences of facial and trigeminal neuropathies were both 29%, but in the 108 patients treated since January 1994, these rates declined to 5% and 2%, respectively. An evaluation of multiple risk factor models showed that maximum radiation dose to the brainstem, treatment era (pre-1994 compared with 1994 or later), and prior surgical resection were all simultaneously informative predictors of cranial neuropathy risk. The radiation dose prescribed to the tumor margin could be substituted for the maximum dose to the brainstem with a small loss in predictive strength. The pons-petrous tumor diameter was an additional statistically significant simultaneous predictor of trigeminal neuropathy risk, whereas the distance from the brainstem to the end of the tumor in the petrous bone was an additional marginally significant simultaneous predictor of facial neuropathy risk. The overall radiological tumor control rate was 93% (59% tumors regressed, 34% remained stable, and 7.5% enlarged), and the 5-year actuarial tumor control rate was 87% (95% confidence interval [CI] 76-98%). Analysis revealed that a radiation dose cutpoint of 10 Gy compared with more than 10 Gy prescribed to the tumor margin yielded the greatest relative difference in tumor growth risk (relative risk 2.4, 95% CI 0.6-9.3), although this difference was not statistically significant (p = 0.207).

CONCLUSIONS

Five points must be noted. 1) Radiosurgery is a safe, effective treatment for small VSs. 2) Reduction in the radiation dose has played the most important role in reducing the complications associated with VS radiosurgery. 3) The dose to the brainstem is a more informative predictor of postradiosurgical cranial neuropathy than the length of the nerve that is irradiated. 4) Prior resection increases the risk of late cranial neuropathies after radiosurgery. 5) A prescription dose of 12.5 Gy to the tumor margin resulted in the best combination of maximum tumor control and minimum complications in this series.

Stereotactic radiosurgery and fractionated stereotactic radiotherapy for the treatment of acoustic schwannomas: comparative observations of 125 patients treated at one institution

BACKGROUND

Stereotactic radiosurgery (SRS) and, more recently, fractionated stereotactic radiotherapy (SRT) have been recognized as noninvasive alternatives to surgery for the treatment of acoustic schwannomas. We review our experience of acoustic tumor treatments at one institution using a gamma knife for SRS and the first commercial world installation of a dedicated linac for SRT.

METHODS

Patients were treated with SRS on the gamma knife or SRT on the linac from October 1994 through August 2000. Gamma knife technique involved a fixed-frame multiple shot/high conformality single treatment, whereas linac technique involved daily conventional fraction treatments involving a relocatable frame, fewer isocenters, and high conformality established by noncoplanar arc beam shaping and differential beam weighting.

RESULTS

Sixty-nine patients were treated on the gamma knife, and 56 patients were treated on the linac, with 1 NF-2 patient common to both units. Three patients were lost to follow-up, and in the remaining 122 patients, mean follow-up was 119 +/- 67 weeks for SRS patients and 115 +/- 96 weeks for SRT patients. Tumor control rates were high (> or =97%) for sporadic tumors in both groups but lower for NF-2 tumors in the SRT group. Cranial nerve morbidities were comparably low in both groups, with the exception of functional hearing preservation, which was 2.5-fold higher in patients who received conventional fraction SRT.

CONCLUSION

SRS and SRT represent comparable noninvasive treatments for acoustic schwannomas in both sporadic and NF-2 patient groups. At 1-year follow-up, a significantly higher rate of serviceable hearing preservation was achieved in SRT sporadic tumor patients and may therefore be preferable to alternatives including surgery, SRS, or possibly observation in patients with serviceable hearing.

Conventionally fractionated stereotactic radiotherapy (FSRT) for acoustic neuromas

PURPOSE

Analysis of local tumor control and functional outcome following conventionally fractionated stereotactic radiotherapy (FSRT) for acoustic neuromas.

PATIENTS AND METHODS

From 11/1989 to 9/1999 51 patients with acoustic neuromas have been treated by FSRT. Mean total dose was 57.6 +/- 2.5 Gy. Forty-two patients have been followed for at least 12 months and were subject of an outcome analysis. Mean follow-up was 42 months. We analyzed local control, hearing preservation, and facial and trigeminal nerve functional preservation. We evaluated influences of tumor size, age, and association with neurofibromatosis Type 2 (NF2) on outcome and treatment related toxicity.

RESULTS

Actuarial 2- and 5-year tumor control rates were 100% and 97.7%, respectively. Actuarial useful hearing preservation rate was 85% at 2 and 5 years. New hearing loss was diagnosed in 4 NF2 patients. Pretreatment normal facial nerve function was preserved in all cases. Two cases of new or impaired trigeminal nerve dysesthesia required medication. No other cranial nerve deficit was observed. In Patients without NF2 tumor size or age had no influence on tumor control and cranial nerve toxicity. Diagnosis of NF2 was associated with higher risk of hearing impairment (p = 0.0002), the hearing preservation rate in this subgroup was 60%.

CONCLUSION

FSRT has been shown to be an effective means of local tumor control. Excellent hearing preservation rates and 5th and 7th nerve functional preservation rates were achieved. The results support the conclusion that FSRT can be recommended to patients with acoustic neuromas where special attention has to be taken to preserve useful hearing and normal cranial nerve function. For NF2 patients, FSRT may be the treatment of choice with superior functional outcome compared to treatment alternatives.

Improved trigeminal and facial nerve tolerance following fractionated stereotactic radiotherapy for large acoustic neuromas

The purpose of this study was to demonstrate improved cranial nerve tolerance following fractionated stereotactic radiotherapy for large acoustic neuromas, defined as tumours with pons-petrous distance (A) > 1 cm and midporous transverse diameter (A + Y) > 2 cm. Of 28 patients with acoustic neuromas treated with fractionated stereotactic radiotherapy, 19 had large tumours at high risk for radiosurgery-induced cranial neuropathy. Six patients received 36 Gy in six, weekly, fractions and 13 patients received 30 Gy in six, weekly, fractions. 15 patients had evaluable trigeminal nerve function and 16 had evaluable facial nerve function. At a median follow-up of 4.5 years, tumour shrinkage was seen in 10 patients and tumour size was stable in nine. None of the patients developed any evidence of transient, or permanent, trigeminal or facial neuropathy at any time during their follow-up period. Fractionated stereotactic radiotherapy may offer a superior therapeutic ratio to single fraction stereotactic radiosurgery in the management of large acoustic neuromas, as evidenced by the absence of post-treatment trigeminal and facial neuropathy.

[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.

Small-field fractionated radiotherapy with or without stereotactic boost for vestibular schwannoma

PURPOSE

To assess the efficacy and toxicity of small-field fractionated radiotherapy with or without stereotactic boost (SB) for vestibular schwannomas.

METHODS AND MATERIALS

Thirty-nine patients with vestibular schwannoma were treated with irradiation between March 1991 and February 1996. Extra-meatal tumor diameters were under 30 mm. Thirty-three patients received small-field fractionated radiotherapy followed by SB. Basic dose schedule was 44 Gy in 22 fractions over 5 1/2 weeks plus 4 Gy in one session. Six patients received small-field fractionated radiotherapy only (40-44 Gy in 20-22 fractions over 5-5 1/2 weeks or 36 Gy in 20 fractions over 5 weeks).dash;p >

RESULTS

Follow-up ranged from 6 to 69 months (median, 24 months). Tumors decreased in size in 13 cases (33%), were unchanged in 25 (64%), and increased in one (3%). The actuarial 2-year tumor control rate was 97%. Fifteen patients had useful hearing (Gardner-Robertson class 1-2) and 25 patients had testable hearing (class 1-4) before irradiation. The 2-year actuarial rates of useful hearing preservation (free of deterioration from class 1-2 to class 3-5) were 78%. The 2-year actuarial rates of any testable hearing preservation (free of deterioration from class 1-4 to class 5) were 96%. No permanent facial and trigeminal neuropathy developed after irradiation. The 2-year actuarial incidences of facial and trigeminal neuropathies were 8% and 16%, respectively.

CONCLUSIONS

Small-field fractionated radiotherapy with or without SB provides excellent short-term local control and a relatively low incidence of complications for vestibular schwannoma, although further follow-up is necessary to evaluate the long-term results.

Linear accelerator radiosurgery for nonacoustic schwannomas

PURPOSE

To analyze the results of nonacoustic schwannomas treated with linear accelerator stereotactic radiosurgery.

METHODS AND MATERIALS

Between August 1989 and October 1997, 18 patients with nonacoustic schwannomas underwent stereotactic radiosurgery at the University of Florida. Nine patients had schwannomas located in the jugular foramen region, seven in the trigeminal nerve, and two in the facial nerve. Nine patients had initial subtotal resections and nine did not undergo surgical intervention. One of the 9 patients with subtotal resection was treated with radiosurgery for a recurrent tumor. Tumor volumes ranged from 0.7 to 15.4 cm3 with a mean volume of 5.5 cm3. Minimal tumor doses ranged from 10.0 to 15.0 Gy with a mean dose of 13.1 Gy. Treatment dose was specified to the 80% isodose shell in 11 patients (58%) and to the 70% isodose shell in the remaining patients. Ten patients (56%) were treated with a single isocenter, 6 patients (33%) with 2-4 isocenters, and 2 patients (11%) with greater than 5 isocenters. Follow-up ranged from 5 to75 months and the mean follow-up was 32 months. Ten patients (56%) had follow-up beyond 2 years and none were lost to follow-up. Local control was defined as clinically stable neurological status and/or stable or decreased tumor size on yearly follow-up MR imaging.

RESULTS

Eighteen evaluable patients (100%) had local control after treatment. All were alive and progression-free at last follow-up. Six of 10 patients with follow-up MRI 2 years or more after treatment had tumor regression and 4 patients had stable disease. Three additional patients with an MRI at 1 year showed no tumor change. Four complications in 3 patients included one worsening of a preexisting VII nerve palsy, 2 patients with new onset of hearing loss, and one with ataxia. No surgical intervention or prolonged steroid use was necessary for any patient with complications. Five patients had improvement in preexisting neurologic deficits.

CONCLUSIONS

Excellent preliminary tumor control rates and a favorable toxicity profile support the effectiveness of linear accelerator stereotactic radiosurgery for patients with nonacoustic schwannomas.

The radiobiology of radiosurgery and stereotactic radiotherapy

Radiation therapy has evolved into a complex amalgamation of treatment techniques that differ significantly according to the way the radiation is delivered to the patient and coincidentally according to the biologic effects that are observed with each technique. Although there are concepts within radiobiology that unify the field, it is not apparent that the biologic effects with one methodology of treatment resemble those of another. Radiosurgery, although initially developed in the 1950s, has become more commonly used in recent years. This treatment involves high-dose, single-fraction treatments with sharp dose gradients to small volumes of tissue. This contrasts with conventional external-beam radiotherapy which involves small-dose, multiple-fraction, broad-dose-gradient treatment to relatively large volumes of tissue. Stereotactic radiotherapy generally delivers small-dose, multiple-fraction treatments to small or intermediate volumes of tissue with a sharp dose gradient compared with conventional external-beam treatment. A discussion of these technique differences with reference to the radiobiologic implications may help elucidate the potential utility of the techniques in clinical radiotherapy.

Vestibular schwannoma management in the next century: a radiosurgical perspective

PURPOSE

To discuss how the evolution of vestibular schwannoma radiosurgery, changes in health care delivery, and patient accessibility to medical information will affect the management of vestibular schwannomas in the future.

CONCEPT

In comparison with microsurgical resection of vestibular schwannomas, radiosurgery has a lower morbidity rate, a similar risk of requiring further surgery, and higher patient satisfaction. As this information becomes more widely available to patients and third-party payors, radiosurgery may replace surgical resection as the preferred management strategy for patients with small to medium sized vestibular schwannomas in the United States.

RATIONALE

It is estimated that 2500 patients are diagnosed with vestibular schwannomas each year in the United States. Assuming that 80% undergo surgery, 2000 operations are performed annually for newly diagnosed vestibular schwannomas. Data available since 1987 regarding the number of cases for which gamma knife radiosurgery was performed were used to predict the number of patients who will undergo vestibular schwannoma radiosurgery in the future. If the current trend continues, an equal number of patients will undergo surgical resection and radiosurgery to treat their vestibular schwannomas (approximately 1000/yr) sometime between 2005 and 2010. Moreover, it is predicted that by 2020, two-thirds of the patients who are newly diagnosed with vestibular schwannomas will undergo radiosurgery, with surgical resection being reserved for patients with large tumors associated with symptomatic brain stem compression.

DISCUSSION

Early data regarding vestibular schwannoma radiosurgery predicted an exponential growth curve. Although it is premature to assume that the current trend will continue, it is likely that an ever increasing percentage of patients will undergo radiosurgery as accessibility to this alternative increases, and more data are published regarding long-term tumor growth control rates. If the mathematical model proves to be accurate, then stereotactic radiosurgery will replace surgical resection as the preferred management strategy for the majority of patients with vestibular schwannomas.

Preliminary results of linear accelerator radiosurgery for acoustic schwannomas

In this paper the authors evaluate the results of linear accelerator (LINAC)-based stereotactic radiosurgery for acoustic schwannomas. Fifty-six patients underwent LINAC-based stereotactic radiosurgery for acoustic schwannomas at the University of Florida between July 1988 and November 1994. Each patient was followed for a minimum of 1 year or until death; no patient was lost to follow up. One or more follow-up magnetic resonance images or computerized tomography scans were obtained in 52 of the 56 patients. Doses ranged between 10 and 22.5 Gy with 69.6% of patients receiving 12.5 to 15 Gy. Thirty-eight patients (68%) were treated with one isocenter and the dose was specified to the 80% isodose line in 71% of patients. Fifty-five patients (98%) achieved local control after treatment. The 5-year actuarial local control rate was 95%. At the time of analysis, 48 patients were alive and free of disease, seven had died of intercurrent disease, and one was alive with disease. Complications developed in 13 patients (23%). The likelihood of complications was related to the dose and treatment volume: 10 to 12.5 Gy to all volumes, three (13%) of 23 patients; 15 to 17.5 Gy to 5.5 cm3 or less, two (9%) of 23 patients; 15 to 17.5 Gy to more than 5.5 cm3, five (71%) of seven patients; and 20 to 22.5 Gy to all volumes, three (100%) of three patients. Linear accelerator-based stereotactic radiosurgery results in a high rate of local control at 5 years. The risk of complications is related to the dose and treatment volume.