Journal of Neuro-Oncology 66: 241–249, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands.
Clinical Study
Linear accelerator-based radiosurgery in the management of skull base meningiomas Chi-Cheng Chuang1 , Chen-Nen Chang1 , Ngan-Ming Tsang2 , Kuo-Chen Wei1 , Chen-kan Tseng2 , Joseph Tung-Chien Chang2 and Ping-Ching Pai2 1 First Division of Neurosurgery, Department of Surgery, 2 Department of Radiation Oncology, Chang Gung Memorial Hospital, Chang Gung University, Linkou, Taiwan, ROC
Key words: LINAC-based radiosurgery, meningioma, radiosurgery, skull base tumor Summary From May 1994 to December 1999, 43 patients with meningiomas in the base of the skull underwent linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) at Chung Gung Memorial Hospital. SRS was performed as a primary treatment in 14 patients, and after resection in 29 patients. The mean tumor volume was 5.68 cc, and the mean target surface dose was 16 Gy, delivered with an average of three isocenters. The median follow-up was 74.5 months. The 7-year local control rate and 7-year overall survival rate were 89.7% and 80.2%, respectively. The 7-year local control was 100% and 84.4% in SRS alone group and surgical excision with SRS group (p = 0.21), respectively. A stationary tumor following SRS was seen in 23 (53.5%) patients, partial shrinkage was seen in 16 (37.2%) patients, and complete disappearance in one patient was seen (2.3%). Furthermore, disease progression was noted in three (7%) patients, one of whom died of disease. The median time to tumor response was 15.4 months (range 5.8–52.8 months). Cases remained stable or had improved neurological statuses without any deterioration in 37.9% and 78.7% of the groups treated with surgery and SRS and SRS alone, retrospectively. In summary, LINACbased SRS is an effective and safe modality of treating unresectable or partially resected meningiomas in the base of the skull. For tumors with diameters of 3 cm or less, particularly in patients without or with minimal clinical neurological symptom, SRS alone can provide a good local control without causing cranial neuropathy. Introduction Meningiomas are among the most common intracranial neoplasms [1,2]. Meningiomas originate in the arachnoid mantle of the brain, and are generally benign, slow growing and well-circumscribed tumors. These tumors are thus generally amenable to complete resection [3,4]. The principal exceptions are tumors of the base of the skull, particularly of the cavernous sinus, where the tumors tend to disseminate to adjacent vital structures and blood vessels [5,6]. Although gross resection is the major treatment for meningiomas in the convexity, anterior third of the sagittal sinus and the posterior fossa dura, this method is not feasible for tumors located in the posterior parasagittal, cavernous sinus, sphenoid wing, orbital, tentorial and clival regions. Despite advances in neuroimaging, anesthesia and microsurgical techniques,
attempted total excision of skull base tumors is associated with permanent neurological deficits, particularly cranial nerve palsies [6,7]. In such cases, subtotal resection combined with adjuvant radiotherapy can achieve results comparable to those of total resection [5,8]. The basic biological effect of stereotactic radiosurgery (SRS) is cellular death and delayed vascular occlusion within the high-dose area. SRS can deliver a sharply focused high dose of radiation to a discrete solitary target while sparing normal surrounding brain [9,10]. This is particularly important for patients with benign intracranial tumors such as meningiomas. SRS aims to preclude tumor progression, preserve existing neurological function and cure symptoms [11,12]. In 1994, linear accelerator (LINAC)-based SRS was instituted at Chang Gung Memorial Hospital. This study presents our experience in using SRS to treat 43 patients with skull base meningiomas.
242 Materials and methods Between May 1994 and December 1999, 93 patients with meningiomas were treated with LINAC-based SRS at Chang Gung Memorial Hospital. The above group contained 43 patients (46.2%) with tumors involving the base of the skull. These 43 patients were taken as the sample group in this study. The median age at treatment was 55.7 years (ranged from 25.7 to 76.3 years), and the sample contained 15 males and 28 females. Tumor locations of all 43 patients are summarized in Table 1. Clinical symptoms included headaches in 10 patients (23%), limb weakness in 5 patients (11.6%) and seizures in 1 patient (2.3%). Thirty-one patients (72.1%) had 57 cranial nerve deficits before treatment, and multiple neuropathies in 10 cases. Among 57 deficits, visual acuity deterioration was seen in 4 patients, blindness in 3 patients, abducent nerve palsy in 4 patients, oculomotor nerve palsy in 2 patients, trochlear nerve palsy in 1 patient, trigeminal neuropathy in 9 patients, facial weakness or palsy in 6 patients, hearing impairment in 8 patients, dizziness in 11 patients, tinnitus in 6 patients and deafness in 3 patients (Table 2). Fourteen (32.5%) patients were treated primarily with SRS, 27 patients (62.8%) received SRS after a prior subtotal resection and 2 patients (4.7%) received SRS as a salvage treatment for tumor re-growth following a prior apparent total excision. Of the 29 patients treated with surgery, 21 patients underwent one course of surgical resection, while 8 patients had two or more prior resections. In patients who had undergone prior open surgical intervention, the mean time to SRS was 20 months (range 0.8–108 months). Table 1. Location of 43 skull base meningiomas treated with LINAC-based SRS Location
No. of tumors
Cavernous sinus Petroclival CPA∗ Sphenoidocavernous Petroclival-cavernous Sphenoidal Sphenoidopetroclival-cavernous Suprasellar Tentorial Tuberculum sellae Optic nerve sheath
11 10 7 4 3 3 1 1 1 1 1
∗
CPA, cerebellopontine angle.
Among 29 lesions with histological available, 1 tumor exhibited atypical histological characteristics, 3 tumors were angiomatous, 7 tumors were transitional, 6 tumors were fibrous and 12 tumors were meningothelial. The 14 patients treated with SRS alone, displayed the standard criteria of MRI characteristics of benign meningiomas. Two patients had received external radiotherapy, one for 50 Gy 6 months before SRS and one for 60 Gy 8.2 years before SRS. All patients were treated with LINAC-based SRS. Multiple non-coplanar arcs radiation was administered with 6-MV photon via the Brain Scan RS Treatment Planning System (Brain Lab, NA Inc.). Patients’ position and tumor localization were fixed with a Cosman–Roberts–Wells (CRW) stereotaxic frame system. A CT scan with a slice thickness of 3 mm was used to localize both the target and the normal critical structures. The treatment target embraced the gross visible tumor by MRI imagines and was supplemented by pre-treatment MRI. The target volume ranged from 0.51 to 35.0 cc with a median of 5.68 cc. Treatment was administered to between one and eight isocenters with a median of three. The 80% isodose curve was used to encompass the target volume, with a median treatment dose of 16 Gy (range 7–25 Gy). The maximum dose administered to the optic apparatus was 8 Gy or less, while that to the brain Table 2. Clinical characteristics and symptoms/signs of 43 patients with skull base meningioma Characteristics Mean age in year
55.7 years (25–76 years)
Sex (no. [%]) Male 15 (34%) Female 28 (65%) Clinical neurological symptoms and signs (no. [%]) Hearing impairment or loss 11 (19.3%) Dizziness 11 (19.3%) Trigeminal neuropathy 9 (15.8%) Visual deterioration or blindness 7 (12.3%) Ocular motor nerves palsies Abducent nerve palsy 4 (7.1%) Oculomotor nerve palsy 2 (3.5%) Trochlear nerve palsy 1 (1.7%) Facial weakness or palsy 6 (10.5%) Tinnitus 6 (10.5%) Total 57 (100%) Previous operation Yes 29 (67%) No 14 (33%)
243 Table 3. Radiosurgery characteristics of 43 patients with skull base meningioma
Clinical results and treatment-related toxicities
Treatment characteristics
Surgery and SRS
SRS alone
Number of patients Median target dose (Gy) Median number of isocenter Median target volume (cc)
29 16 (7–25) 4 (1–8) 5.2 (0.51–32.7)
14 18 (8–20) 3 (1–5) 9.8 (0.8–35)
Operation and SRS group Clinical neurological deficits pre-operatively improved partially or totally following resection and before SRS in 5 patients. One patient had undergone gross total excision of tumor and 4 patients had a subtotal excision of tumor. Six of the 29 patients remained unchanged neuropathies without recovery or improvement. Overall, cases remained stable or had improved neurological statuses without any deterioration in 11 of the 29 patients (37.9%). Eighteen of the 29 patients (62.1%) presented new or worsened cranial neuropathies post-operatively. All developed immediately or within 1 month after operation with a median time of 3 days. Seven of these 18 patients had temporary cranial neuropathies following surgical resection, and 4 of these 7 patients had multiple cranial nerve deficits. Four patients exhibited temporary extraocular muscle dysfunctions (3 patients had abducent nerve palsy and 1 patient had oculomotor nerve palsy), 3 patients suffered trigeminal nerve deficits, 2 patients had hearing impairments but still serviceable, one had tinnitus and 3 patients had ptosis. The temporary neurological deficits were all recovered in their following courses with a median time of 3.6 months (range of 2.1–8.4 months). A further 11 patients displayed new permanent cranial neuropathies after resection that persisted at the time of last follow-up. Among these 11 patients, a new onset of permanent ptosis was seen in 4 patients, facial palsies in 2 patients, abducent nerve palsy in 3 patients, visual acuity deterioration in 2 patients, trigeminal nerve deficit in 1 patient, dysphagia in 1 patient and complete hearing loss with imbalance in 1 patient. One of these 11 patients had experienced dysphagia, and complete hearing loss immediately and dizziness within 2 days since resection, and no obvious improvement of hearing function and imbalance after oral steroid medication. He exhibited slowly progressive imbalance starting 2 days after SRS. Because of the short interval between operation and SRS (24 days), it was ascribed to operation-induced nerves damage. Eight of these 11 patients had multiple cranial nerve deficits. After SRS, one case recovered partially from facial numbness at 10-month follow-up. Two (6.9%) exhibited new persistent neuropathies. One developed a unilateral facial palsy 9.8 months after SRS with an interval of 3.8 months between operation and SRS.
stem was 12 Gy or less. The maximum irradiation dose, isodose and margin dose delivered were determined jointly by the neurosurgeon, radiation oncologist and medical physicist. Five patients received SRS twice (median dose: 8 Gy) with a 2-week interval. All patients were admitted before the day of SRS, and discharged next morning after SRS. Table 3 lists the SRS treatment characteristics of the 43 patients, including whether or not they had a history of previous surgery. All patients were included in a prospective followup program. Local response was evaluated according to clinical examinations and MRI. Tumor control after SRS was defined as no change or any decrease in tumor volume on follow-up MRI studies comparison with that at the time of SRS. Any increase in tumor volume radiologically was defined as disease progression. The radiological statuses of the tumors were assessed by a neurosurgeon, radiologist and radiation oncologist, to not only record changes in tumor size but also compare relative locations of tumors with adjacent normal brain structures. The first clinical examination was evaluated 4–6 months after SRS, and then repeated every 6 months for the first 2 years and yearly thereafter. Survival and local control rates were analyzed using the Kaplan–Meier method. Cox proportional hazards regression was used to analyze univariate associations between potential risk factors of interest and each of the outcome variables and to estimate relative risks and corresponding 95% CIs for each risk factor. The score test was used to evaluate the statistical significance of each risk factor. The statistical analysis was performed in December 2002.
Results The median follow-up period for SRS was 74.5 months (range 10.3–105.4 months).
244 Another one developed hearing impairment 6 months after SRS with an interval of 2.7 months between operation and SRS. SRS alone group After a median follow-up of 74.5 months, 8 of the 14 patients (57.1%) remained totally unchanged neurological functions, including 3 patients with normal cranial nerves pre-SRS. In the other 6 patients, they displayed variously complete recovered, partial improvement, worsening, or new onset of nerve deficits in their follow-up course. Among patients who experienced improvement or worsening of pre-treatment neuropathies, one had a partial decrease in facial pain with completely recovered from dizziness 12 months after SRS, one completely recovered from abducent nerve palsy but a new onset of dysphagia, one gradually recovered from facial numbness after 1-year follow-up, one experienced less facial palsy at the last follow-up and 1 patient suffered deterioration of visual acuity 8 months after SRS but not to an extent that interfered with daily activities. The last one was a 26-year-old woman treated in May 1994 with normal neurological function before SRS. She presented progressive left side weakness at 6-month follow-up. In this case, with a left cerebellopontine angle mass, the tumor margin had received 18 Gy delivered in the 80% isodose. However, the brain stem was exposed to a 1620-cGy dose. Among 3 patients with new onset of nerve deficits, one had temporary abducent nerve palsy at a follow-up time of 10 months that subsided 4 months after steroid therapy, and one presented with oculomotor nerve palsy
at a follow-up time of 18 months after SRS and had no recovery in spite of protracted steroid therapy. Overall, 11 of the 14 patients (78.7%) remained stable or had improved neurological status without any deterioration. Risk factors associated with complications following SRS were calculated by univariate analysis included age, sex, number of isocenters, target volume, a history of prior resection, target dose and maximal SRS dose. None of these factors was a determining factor for complications. Table 4 summarizes the neurological changes following treatment of the entire group. Tumor control Objective assessments of tumor control were based on assessments from MRI scans in all patients. The 7-year local control rate for all patients was 89.7%. Partial tumor shrinkage was observed after SRS in 16 patients (37.2%), complete disappearance in 1 patient (2.3%) and stable disease in 23 patients (53.5%). Tumor responses occurred after intervals of 5.8–58.8 months following SRS (median: 16.5 months). Tumor progression was noted in 3 patients (7%). One patient died of recurrent disease 55 months after SRS, and one remained alive despite disease progression at 6-year follow-up. Another patient with atypical histology underwent two total excisions 5.2 and 1.7 years before SRS. Unfortunately she suffered from local progression 2.4 years after the initial SRS, and was then treated with a third subtotal excision and a second SRS treatment.
Table 4. Changes of cranial nerves statusesa of 43 patients with skull base meningioma after treatment Operation and SRS group (n = 29) NSb following surgery Improved Decreased VAc Ptosis Oculomotor neuropathy Abducent neuropathy Trigeminal neuropathy Facial palsy Hearing impairment Tinnitus Dysphagia a
2 2 2 1
Transient 3 1 3 3 2 1
NS following SRS Permanent
Improved
Transient
NS following SRS Permanent
Improved
Transient
2 4
Permanent 1 1
3 1 2 1 1
Some patients revealed more than one cranial neuropathies. NS, neurological status. c VA, visual acuity. b
SRS alone group (n = 14)
1 1 1
1 2 1
1
1
245
Figure 1. Graph showing the local tumor control rates in patients treated with SRS alone (dotted line), as wall as resection with SRS (solid line) for skull base meningiomas. There is no statistically significant difference in local control for the two groups of the study (p = 0.21).
Among the 14 patients who received SRS as their primary treatments, 8 patients (57.1%) had tumors whose sizes remained constant, 5 patients (35.7%) experienced partial shrinkage and one achieved complete regression. The 7-year local control was 100% following SRS alone and 84.4% following surgical excision plus SRS (p = 0.21) (Figure 1). All clinical and treatment variables were determined by univariate analysis, including age, sex, history of prior resection, time interval between diagnosis and SRS, SRS target volume and SRS target dose. No prognostic factor was statistically significant with respect to local control. Survival Six deaths occurred among 43 patients during the follow-up period. A 66-year-old male died of multiple myeloma; a 65-year-old male died of pneumonia 39 months after SRS; a 63-year-old female died of acute myocardial infarction; a 71-year-old female died 49 months after SRS without documented cause; and a 45-year-old female died from a traffic accident 2 months after SRS. Only one patient died of tumor recurrence. Therefore, the 7-year overall and diseasefree survival rates were 80.2% (Figure 2) and 78.9%, respectively.
Discussion Subtotal excision combined with adjuvant radiotherapy for patients with meningiomas is widely accepted to result in outcomes equivalent to total excision
Figure 2. Graph showing the overall survival rate in patients treated with SRS for skull base meningiomas, as analyzed using the Kaplan–Meier method.
[5,8,13]. Patients who only received subtotal excision had inferior local control rates and disease-specific survival. Although maximal surgical intervention is an effective treatment for most benign meningiomas, invasive excisions of tumors of the skull base are often associated with neurological deficits [14,15], and damage to adjacent cranial nerves can result in temporary or permanent neurological deficits in 15–50% of cases [16,17]. Owing to effective results from applying SRS to skull base schwannomas and encouraging outcomes of fractionated external radiotherapy for partially excised meningiomas [10], SRS was considered an appropriate alternative treatment strategy for small- to moderate-sized skull base meningiomas [18]. In our study, the local control is comparable to that of previous by published results [19,20], especially in the SRS alone group, although longer follow-up is needed to determine the final treatment outcome. Table 5 summarizes the recently published results of skull base meningiomas treated with Gamma-knife and LINAC-based SRS [11,20–26]. The evaluation of cranial nerve deficits after treatment was quite complicated for tumors located at the skull base. After treatment, some cases had improvement of or complete recovery from pre-treatment neuropathies, however, many also experienced new treatment-induced CNS toxicities at the same time. In the groups treated with surgery with SRS and SRS alone, cases remained stable or improved without any deterioration in 11 (37.9%) and 11 patients (78.7%), retrospectively. We did not analyze statistically the difference of changes in cranial nerve statuses between them because of the small sample size for both groups. Nevertheless, we found that the group treated with SRS
246 Table 5. Radiosurgery for skull base meningiomas No. of patients
Prior treatmenta (OP/EXRT)
Mean target volume (cc)
Mean target dose (Gy)
Follow-up time (months)
Local control rate (%)
Gamma-knife SRS Nicolato et al. (1996)
50
28/0
8.6 (0.06–20)
18 (10–28)
14
98
Subach et al. (1998)
62
39/7
13.7 (0.8–56.8)
15 (11–20)
37
100
Pendl et al. (1997) Pollock et al. (2000) Roche et al. (2001) LINAC-based SRS Chang et al. (1997)
97 148 92
53/0 117/18 30/1
13.7 (0.8–82) 7.7 (0.6–30.4) 4.7 (0.9–18.6)
18.5 (6–46) 16 (12–20) 15 (6–25)
18.5 37 24
96 91 (7-year) 95
55
38/5
7.3 (0.5–2.8)
18.3 (12–25)
48.4
98
4.1 (0.2–51)
15 (9–20)
31 (1–80)
89 (5-year)
12.7 (10–20) 16 (7–25)
23 (2–88) 74.5 (10–105)
Hakim et al. (1998)
82/127d
—
Shaforn et al. (1999) Present study (2003)
30/70e 43
— 29/2
10 (0.6–28) 5.7 (0.5–35)
100 89.7(7-year)
Complication (%)
4 (TRb ) 2 (PERc ) 3 (TR) 5 (PER) — 13.5 4 18 (TR) 7 (PER) 3 (TR) 1.6 (PER) 3 (PER) 9.3 (PER)
a
Numbers of patients received prior operation or external radiotherapy. TR, transient neurological complication. c PER, persistent neurological complication. d 82 of 127 patients had skull base meningiomas. e 30 of 70 patients had skull base meningiomas. b
alone seemed to have a higher probability of maintaining a stable or improved neurological status after treatment, especially in those with minimal or no initial neurological symptoms. One developed hearing deterioration 8.7 months after resection with an interval between operation and SRS of 6 months. As hearing impairment associated with microsurgery tends occur in the months after the operation with a maximum delay of 2 or 3 years [27–29], it is hard to infer that the operation or the SRS was the definite cause of hearing impairment in this case. This study found 5-year local control rates for patients with previous surgical resection plus SRS versus those with primary SRS alone of 89.6% and 100% (p = 0.21), respectively. There is no statistical difference between these two groups. It may be that the study groups with and without previous resections differed slightly in local control. Therefore a larger sample size would be required to analyze the statistical significance. If the difference existed, one possible cause of lower local control in the group with resection and SRS may be that post-operative changes around the tumor may obscure definition of SRS target. If SRS target included suspicious enhancement in images other than real tumor, overestimation of the tumor will compromise delivery of radiation dose because of the risk of treating a larger volume. On the other hand, if real
tumor was underestimated because a part of it was undifferentiated with post-operative changes and, thus, this part of real tumor will be out of SRS treatment field. On the contrary, this minor discrepancy in local control between the groups with and without previous resections in this study may be attributed to an atypical histology in one of the 3 patients who suffered from local progression. Atypical meningiomas are frequently associated with high recurrence rates [2,30]. Increased cellularity and high mitotic rates had been defined in this variant. Since SRS can deliver a highly concentrated and homogenous radiation dose distribution to a tumor mass while limiting the dose to the surrounding normal tissue, it may miss some tumor cells lying outside the radiographic gross tumor mass of atypical meningiomas [10,25,31]. Consequently, external conformal radiotherapy for partially resectable or unresectable atypical meningiomas is suggested to overcome this problem [10,31]. Chang and Adler [11] reported on the treatment of 55 patients with cranial base meningiomas by the Stanford University group. Twenty-four patients had not undergone any previous resection. The target was treated with a mean dose of 18.3 Gy, and the 2-year actuarial local control rate was 98%. Thirty-eight (69%) patients reported no change in radiographic status with a median follow-up of 48.4 months.
247 Meanwhile, permanent neurological complication was noted in 4 patients (7%), 2 of whom developed new neuropathies at between 9 and 12 months. Kondziolka et al. [12] published their long-term experience of all meningiomas undergoing SRS at the University of Pittsburgh. Forty-two out of the 99 patients did not undergo surgical resection (median target dose 16 Gy). Five patients (4.8%) developed SRS-related neuropathies within 31 months following SRS, compatible with our results. Besides, Kondziolka et al. reported that 26 patients (49.5%) experienced tumor shrinkage at 4–10 years. We hope that the 23 patients with unchanged tumor volume in this present investigation will display a delayed reduction in tumor size with a longer follow-up time. Kondziolka et al. [12] also reported that local tumor progression after SRS was related to a history of prior operation (p = 0.02). Owing to advances in neuroimaging, more and more skull base meningiomas are being diagnosed incidentally. Subach et al. [20] suggested using serial neurodiagnostic imaging for asymptomatic patients with petroclival meningiomas and that treatment, regardless of resection or SRS, should be reserved for the time of symptoms occurrence or tumor progression. However, masses growing at the base of skull may lead to permanent neuropathies and complicate further treatment regardless of the surgery or SRS performed. According to previous literature, SRS can provide a potential curative control with acceptable neurological complications in patients with skull base meningiomas with tumor sizes below 3 cm. Furthermore, Kondziolka et al. [12] had reported that patients with long-term survival were satisfied and viewed SRS as a successful treatment subjectively. Therefore, SRS alone may be valuable for asymptomatic patients who want to receive early treatment over observation. In symptomatic patients with tumors smaller than 3 cm and who cannot tolerate the operation procedure owing to medical problems or old age, or who were refused operation, primary SRS is a good and safe alternative strategy with excellent local control and an acceptable mortality rate [12,18]. In symptomatic patients with tumors smaller than 3 cm who are candidates for surgery, primary resection without compromising neurological status is suggested. SRS may be considered following subtotal excision or as salvage for recurrence following grossly total excision. In patients with tumors larger than 3 cm, an aggressive total excision was not suggested for skull base meningiomas, despite the existence of clinical symptoms. The major role of surgical resection for large
skull base tumors should be to relieve mass effect and decompress. Aggressive surgery for skull base tumors, a hard to access site with complicated anatomy, may result in 20–62% incidence of new or worsened neurological deficits and a 7–16% incidence of permanent post-operative major neurological deficits, not to mention a 2–4% mortality rate [6,7,16]. Therefore, strategy of subtotal resection followed by SRS for initial tumor sizes larger than 3 cm is recommended for skull base meningiomas, which often intrude into cavernous sinus and encase critical vascular structures. Although no precise relationship has been noted between the maximal tolerated dose to many cranial nerves and subsequent complications [32], cranial nerves of the cavernous sinus other than optic structures appear very tolerant to a single large dose of radiation, up to a maximum dose of as much as 40 Gy. Regarding the radiation tolerance of optic apparatus, some reports recommended that the maximum radiosurgical dose should be limited to below 8–10 Gy [33]. Meanwhile, Morita et al. [34] reported the results of 95 patients with skull base meningiomas treated at the Mayo Clinic. Despite the lack of relevant data on the radiosurgical dose to the visual pathway, the author assumed that the optic apparatus seemed to tolerate doses above 10 Gy and a maximum dose of up to 16 Gy if a short segment of the visual pathway was irradiated. The author assumed that a radiosurgical dose of at least 15–16 Gy was required for tumor control, and that a restriction on radiation doses of below 8 Gy to optic apparatus may deliver a suboptimal radiation dose and consequently increase the risk of tumor progression. Presently, using a dynamic multileaf collimator and intensity-modulated SRS (IMSRS) it is possible deliver an improved radiation dose distribution for small and irregularly formed skull base lesions [35], especially for lesions near to the brain stem or optic apparatus. It is logical that improved radiation dose conformity will minimize the risk of toxicity because since normal critical tissues will receive less radiation [36]. In conclusion, SRS is an effective and safe treatment modality for skull base meningiomas. For tumor of 3 cm or less in size, primary SRS can provide good tumor control with acceptable neurological complications, especially in patients without obvious symptoms. Meanwhile, for tumors larger than 3 cm, multiple treatment modalities are recommended, including partial resection plus SRS. Since patients with benign diseases often survive for a long time, choosing the best and suitable treatment strategies without compromising patient quality of life is also an important consideration.
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conformity of gamma knife radiosurgery and risk factors for complications. Int J Radiat Oncol Biol Phys 51: 1313–1319, 2001 Address for offprints: Ping-Ching Pai, Department of Radiation Oncology, Chang Gung Memorial Hospital, 5 Fu-Shin Street, Kwei-Shan Hsiang, Taoyuan, Taiwan, ROC; Tel.: 886-3-3281200 ext. 2600, 2604; E-mail:
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