Clinical investigation
Brain
Twenty years’ experience in the treatment of acoustic neuromas with fractionated radiotherapy: A review of 45 cases

https://doi.org/10.1016/j.ijrobp.2006.04.017Get rights and content

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.

Introduction

The traditional treatment of acoustic neuromas (AN) is surgery, which provides excellent tumor control rates when tumor excision is complete (1, 2). In our institution, surgical excision remains the standard treatment for AN. The aim of surgery is complete resection with VIIth cranial nerve preservation and, in some cases, hearing preservation (3, 4). Nevertheless, total removal is not always feasible without significant morbidity, and in some cases the patient’s condition contraindicates surgery.

Stereotactic radiosurgery (SRS) has been proposed as a noninvasive and efficacious alternative to surgery (5, 6, 7, 8). With the introduction of linear accelerators adapted for SRS, the results are comparable to those obtained with γ-knife units (9, 10, 11, 12, 13). However, indications for SRS are clearly restricted to small tumors because it is known that the incidence of facial and trigeminal neuropathies increases with the length of irradiated Vth or VIIth cranial nerves (14). In addition, the damage rates are dependent on the dose delivered, which in turn is linked to the size of the tumor (7, 15, 16, 17, 18).

Fractionated radiotherapy (FRT) is another alternative to surgery, especially in large tumors. Clinical and biologic studies suggest that the therapeutic ratio of radiotherapy (RT) increases with increased fractionations because the risk of injury to normal structures (cranial nerves and brainstem) will be reduced with daily low doses (19, 20).

The efficacy and low toxicity of conventional FRT have been documented during the last two decades. Wallner et al. reported on postoperative irradiation for incompletely excised acoustic neuromas (21). In three previous studies, we demonstrated that static-beam FRT for Stage III and IV neuromas provided excellent local control with a low rate of toxicity (22, 23, 24).

Furthermore, Linac-based stereotactic fractionated radiotherapy (FSRT) gives comparable control rates to those reported with SRS, without the morbidity of the single-dose of RT, even if no randomized study has been performed to compare the two techniques. In some series, fraction doses are low (1.8–2 Gy) and median total doses range from 50 to 58 Gy (20, 25, 26, 27, 28, 29, 30, 31, 32). In others, a hypofractionated schedule is employed with fraction doses of 3 to 5 Gy and total doses of 20 to 30 Gy (33, 34, 35, 36, 37). Definitive facial and trigeminal toxicity are low, and few cases of malignant transformation have been reported (38, 39, 40).

The present series reports our very long-term experience in FRT of AN.

Section snippets

Patients

From January 1986 to January 2004, 45 consecutive patients (20 males, 25 females) with AN were treated in our department. Ages ranged from 16 to 84 years (median, 76 years). No patients were excluded, but three were lost to follow-up. Information was available about their outcome 14, 84, and 142 months after FRT. Nine patients had phacomatosis, including one with tuberous sclerosis and eight with neurofibromatosis 2 (NF2) disease. One patient was successively irradiated in both sides.

Before

Results

The main objective of the present study was to determine tumor response, local tumor control, and tolerance after FRT. Patient and tumor outcomes are given in Table 2. The median follow-up after FRT was 80 months (range, 4–227 months). All patient follow-up data were updated as of December 2005.

Discussion

The purpose of this study was to determine very long-term results of FRT measured by the rate of local control and tolerance. With a median follow-up of 80 months (range, 4–240 months), this radiation technique given to selected patients with general contraindications for surgery and/or large tumors for most of them seems efficient over time. Most of our patients presented with aggressive tumors: seven had ventricular shunts before FRT and more than 50% presented with associated neurologic

Conclusions

This long-term follow-up study follows on from a preliminary report (22) and provides insights into the outcome of AN patients carefully selected to receive FRT in an institution where simulation and treatment reproducibility were of good quality. FRT has led to very good long-term results but needs long-term follow-up because of the possibility of very late recurrences and malignant transformation. Caution is particularly required when treating young patients.

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