Pediatric Intracranial Arteriovenous Malformation: Long-Term Outcomes with Linear Accelerator (LINAC)-Based Radiosurgery.

PURPOSE: To analyze and report the long-term outcomes of intracranial arteriovenous malformations (AVM) treated with linear accelerator (LINAC)-based radiosurgery (LBRS) in the pediatric population. METHODS AND MATERIALS: A series of 34 pediatric patients (≤18 years old) who were treated between 2002 and 2016 were analyzed. All patients were treated with LBRS in a single fraction, with a median dose of 16.8 Gy to the 80% isodose line. Median age at treatment was 14.4 years (range 5.5-18.9). Median AVM volume was 2.91 mL (range 0.228-27.313). Median modified radiosurgery-based AVM score was 0.83 (range 0.18-2.96). The most common presenting symptom was intracranial hemorrhage (ICH) (n = 22, 64.7%). Nine patients underwent intervention before LBRS, which included prior embolization or resection. Seven lesions were in eloquent locations, defined as basal ganglia, thalamus, or brainstem. Cerebral angiography was done to confirm obliteration. RESULTS: Median follow-up time was 98 months (range 36-200 months). Twenty-two of the 34 lesions were obliterated (64.7%) with median time to obliteration of 37 months (range 14-79). No deaths occurred during the follow up period; however, two patients experienced ICH after treatment. Three other patients were treated for symptomatic radiation necrosis. CONCLUSIONS: Treatment of intracranial AVM with LBRS in the pediatric population is demonstrated to be safe and effective with long-term follow up.

A comparative outcomes analysis of patients treated for arteriovenous malformation with LINAC-based stereotactic radiosurgery by a standard frame-based technique or a frameless technique utilizing 3-dimensional rotational angiography.

Previous work at our institution treating arteriovenous malformation (AVM) with radiosurgery (RS) demonstrated superior nidus visualization and geometric accuracy with use of 3-dimensional rotational angiography (3DRA) compared to biplanar digital subtraction angiography. We have since adopted a unique radiosurgical protocol that utilizes 3DRA in the planning of linear accelerator (LINAC)-based RS delivered in a frameless manner. This study seeks to compare clinical outcomes between patients treated by this novel approach and those treated by our historic frame-based protocol. Clinical data were queried for all patients treated for AVM by single-fraction RS from 2003 to 2017. RICs were identified and classified as radiologic, symptomatic, or permanent. Excellent outcome was defined as nidus obliteration without intracranial hemorrhage (ICH) or symptomatic RIC. Clinical predictors of study outcomes were identified through univariate and multivariate logistic regression using backwards elimination to optimize a predictive model. 131 AVMs in 124 patients were included with a median follow-up of 88 months. 59 AVMs received frame-based RS and 72 AVMs received frameless RS. Rate of obliteration was 64% for frame-based RS and 61% for frameless RS (p = 0.70). Radiologic, symptomatic, and permanent RICs rates were 68%, 17%, and 8%, respectively, for frame-based cases, versus 40% (p < 0.01), 8% (p = 0.13), and 3% (p = 0.15), respectively, for frameless cases. Excellent outcome was achieved in 49% of frame-based cases and 53% of frameless cases (p = 0.68). These results illustrate the safety and effectiveness of frameless LINAC-based AVM RS utilizing 3DRA.

Long-Term Outcomes of Newly Diagnosed Resected Atypical Meningiomas and the Role of Adjuvant Radiotherapy.

OBJECTIVE: The role of adjuvant radiotherapy (ART) in patients with World Health Organization Grade II atypical meningiomas (AMs) remains controversial. METHODS: We retrospectively reviewed 149 patients with newly diagnosed resected AMs from 2000 to 2012. Gross total resection (GTR) was defined as Simpson Grades I-III and subtotal resection (STR) as Grades IV and V. Kaplan-Meier analyses of local control (LC), progression-free survival (PFS), and overall survival were performed with the log-rank test, and risk factors for progression/recurrence (P/R) were analyzed with multivariate Cox regression. RESULTS: Median follow-up was 74.2 months. GTR was achieved in 98 patients and STR in 51 patients. Fifty-three (35%) patients received ART. Overall, 46 patients (31%) experienced P/R with a median time to P/R of 32.4 months. ART was associated with a trend toward improved PFS (P = 0.0669) in the GTR subset but significantly improved LC (P = 0.0183) and PFS (P = 0.0034) in the STR subset. Age, tumor size, and STR were significant risk factors for worse PFS, whereas receiving ART was associated with improved PFS on multivariate analyses. Thirty-nine of the 46 progressive/recurrent patients underwent salvage therapy with only 22 patients experiencing long-term control. Five patients experienced transformation to World Health Organization Grade III malignant meningioma. CONCLUSIONS: Patients who undergo STR for newly diagnosed AM should receive ART based on improvements in LC and PFS. GTR patients should be considered for ART, but active surveillance is a reasonable management approach with the recognition that progressive/recurrent disease can act aggressively. Prospective, randomized trials are currently underway to evaluate the role of ART.

De novo superior cerebellar artery aneurysm following radiosurgery for trigeminal neuralgia.

Stereotactic radiosurgery is a commonly used method for treatment of trigeminal neuralgia. Radiation has been known to be a factor in the later development of aneurysms. Aneurysms have been reported to occur after radiation delivered in a variety of methods including both externally delivered radiation radiosurgery and brachytherapy. We report here an incidence of a de novo aneurysm presenting following radiosurgery treatment for trigeminal neuralgia. The patient was treated using frame-based LINAC radiosurgery receiving 90Gy to the mid cisternal extent of the nerve via a 4mm conical collimator. The patient presented with progressive hypoesthesia 11years after treatment. Imaging evaluation demonstrated the presence of an aneurysm abutting the treated trigeminal nerve. The aneurysm was successfully coil embolized. The patient's facial hypoesthesia, however, did not improve following embolization. We believe that this is the first report of such an aneurysm occurring after radiosurgery for trigeminal neuralgia. De novo aneurysms are a recognized long term complication of radiotherapy and radiosurgery treatment. This report shows such aneurysms can occur with very small treatment volumes. Late sensory changes following radiosurgery for trigeminal neuralgia should prompt workup for de novo aneurysms as well as other late adverse radiation effects.

Hypofractionated stereotactic radiosurgery for treatment of cerebral arteriovenous malformations: outcome analysis with use of the modified arteriovenous malformation scoring system.

Radiosurgery has long been an accepted modality for definitive treatment of cerebral arteriovenous malformations (AVM). Efforts to improve the therapeutic ratio for this indication include use of staged volume procedures and hypofractionation. This study reviews our experience with a cohort of patients treated with hypofractionated radiosurgery. Over a 3year period, 38 patients harboring 39 cerebral AVM were treated with hypofractionated stereotactic radiotherapy. Seventeen of these patients presented due to hemorrhage, four were asymptomatic unruptured lesions and the remainder were symptomatic unruptured lesions. The median AVM volume was 11.43 cc and median modified Radiosurgery-Based Arteriovenous Malformation Score (mRBAS) was 2.02. The median follow-up was 7.32years. Four patients harboring four AVM were lost to follow-up before a result could be ascertained leaving 35 AVM for analysis. Excellent outcomes (AVM obliteration without new deficits) occurred in 17 of 34 (50%) patients and in 18 of 35 (51%) AVM treated. AVM obliteration was seen in 26 of 35 (74%) lesions treated. Two patients died during the follow-up period (6%). A poor result (major deficit without obliteration) was seen in one patient. Of 19 patients harboring AVM with mRBAS >2.0, an excellent outcome was achieved in eight (42%). Hypofractionation for cerebral AVM can result in satisfactory obliteration rates, but with risk of significant complications commensurate with mRBAS. Further study of this technique will be needed to ascertain the degree of incremental improvement, if any, over other radiosurgery treatment methods.

Integral Whole Brain Dose from Stereotactic Radiosurgery of 47 Metastatic Lesions: A Dosimetric Case Study.

This report describes the case of a 15-year-old male diagnosed with primary ALK-positive adenocarcinoma of the lung metastatic to the brain. He was treated with surgical resection for a single lesion followed by whole brain radiotherapy and subsequently underwent 10 courses of stereotactic radiosurgery for 47 lesions delivered over a four-year period. Currently, all metastatic lesions in the brain are completely resolved or locally controlled.

A comparative study of stereotactic radiosurgery, hypofractionated, and fractionated stereotactic radiotherapy in the treatment of skull base meningioma.

OBJECTIVES: To compare the outcomes of skull base meningiomas treated with stereotactic radiosurgery (SRS), hypofractionated stereotactic radiotherapy (hFSRT), and fractionated stereotactic radiotherapy (FSRT). METHODS: A total of 220 basal meningiomas in 213 patients were treated using SRS (N=55), hFSRT (N=22), and FSRT (N=143). The median age was 59 years (28 to 84 y). Prior surgery was performed in 74 cases; 39 patients received adjuvant radiotherapy after incomplete resection and 35 patients received salvage radiotherapy after tumor progression. In 146 cases, radiation was the primary therapy. Ten patients had World Health Organization II or III meningiomas. RESULTS: The median follow-up was 32 months (7 to 97 mo). Median tumor volume was 2.8 cm (0.10 to 16.94 cm), 4.8 cm (0.88 to 20.38 cm), and 11.1 cm (0.43 to 214.00 cm) and the median dose was 1250 cGy in 1 fraction to the 80% isodose line (IDL), 2500 cGy in 5 fractions to the 90% IDL, and 5040 cGy in 28 fractions to the 90% IDL for the SRS, hFSRT, and FSRT groups, respectively. Radiographic control was achieved in 91%, 94%, and 95% (P=0.25), whereas clinical response was seen in 89%, 100%, and 91% (P=0.16) in the SRS, hFSRT, and FSRT groups, respectively. CONCLUSIONS: There is no significant difference in the radiographic and clinical response in patients with skull base meningioma treated with SRS, hFSRT, or FSRT and thus gives the clinician the impetus to tailor treatment techniques to the location and size of the tumor at presentation.

Photon-based fractionated stereotactic radiotherapy for postoperative treatment of skull base chordomas.

OBJECTIVES: We report our series of skull base chordoma patients who underwent surgical resection followed by high-dose fractionated stereotactic radiotherapy (FSRT) as an alternative to proton radiotherapy (RT). METHODS: Between 2002 and 2009, 12 patients with skull base chordomas without prior radiation history were treated with adjuvant or salvage RT. FSRT with dynamic conformal arcs and intensity-modulated radiation therapy boost was used until 2006 when image-guided intensity-modulated FSRT was instituted. Median dose of 66.6 Gy (range, 48.6 to 68.4 Gy) was delivered in 180 cGy fractions prescribed to the 90% isodose line that covered the target volume to achieve a median isocenter dose of 74 Gy (range, 54 to 76 Gy). RESULTS: Median follow-up was 42 months. Median time from surgery to initiation of RT was 3.6 months. Overall survival was 76.4% at 5 years, and 46.9% and 37.5% of patients were free of progression at 24 and 60 months, respectively. Six patients had disease progression after radiation with a median time to progression of 17.3 months. One patient was salvaged with radiosurgery and surgical resection, with stable disease almost 7 years since diagnosis. Two patients were salvaged with molecular targeted therapy with stable disease at 20 and 23 months. At last follow-up, 9 patients had stable or reduced disease. CONCLUSIONS: FSRT as postoperative treatment of skull base chordomas resulted in promising overall survival results comparable with the published literature of particle therapy without significant complications. Our technique for treating skull base chordomas can be considered a safe and less costly alternative to proton RT.

Frameless image-guided radiosurgery for initial treatment of typical trigeminal neuralgia.

OBJECTIVE: To review retrospectively initial experience at a single institution using frameless image-guided radiosurgery (IGRS) for trigeminal neuralgia employing the Novalis linear accelerator (LINAC) with ExacTrac robotic patient positioning device. METHODS: Over an 18-month period, 44 patients (27 women and 17 men; median age 65 years) were treated with frameless IGRS for typical trigeminal neuralgia (14 cases involved left-sided pain and 30 cases involved right-sided pain), responsive to anticonvulsant medications, with Barrow Neurological Institute Pain Scale (BNI-PS) scores of 4 or 5. All cases were initial radiosurgery treatments with an isocenter dose of 90 Gy delivered via a 4-mm circular collimator forming a spheroid dose envelope. Intrafraction positioning data were collected for all patients. The median follow-up was 15 months. RESULTS: Overall intrafraction positioning error was 0.49 mm ± 0.44. After treatment, 40 patients achieved a BNI-PS score of IIIb or better; 19 patients achieved a BNI-PS score of I. The median time to pain relief was 4 weeks. Overall, new hypoesthesia was seen in five patients. No other complications were seen. CONCLUSIONS: Use of frameless IGRS methods for treatment of trigeminal neuralgia showed results similar to the authors' prior experience with frame-based treatment methods. IGRS using frameless methods is a suitable treatment method for patients with trigeminal neuralgia and may be applicable to other functional indications.

Control of brain metastases using frameless image-guided radiosurgery.

OBJECT: Radiosurgery is an important and well-accepted method in the management of brain metastases. Using conventional frame-based techniques, high lesional control rates are expected. The introduction of image-guided techniques allows for improved patient comfort and workflow. Some controversy exists as to the accuracy of imageguided techniques and consequently the impact they might have on control of brain metastases (as opposed to the level of control achieved with frame-based methods). The authors describe their initial 15-month experience with image-guided radiosurgery (IGRS) using Novalis with ExacTrac for management of brain metastases. METHODS: The authors reviewed the cases of brain metastasis treated by means of IGRS in their tertiary regional radiation oncology service over a 15-month period. During the study period 54 patients (median age 57.9 years) harboring 108 metastases were treated with IGRS. The median time from cancer diagnosis to development of brain metastasis was 12 months (range 0-144 months). The median tumor volume was 0.98 cm(3) (range 0.03-19.07 cm(3)). The median prescribed dose was 18 Gy to the 80% isodose line (range 14-20 Gy). Lesions were followed with postradiosurgery MR imaging every 2-3 months following treatment. RESULTS: The median follow-up period was 9 months (range 0-20 months). Median actuarial survival was 8.6 months following IGRS. Eight patients with 18 lesions died within the first 2 months after the procedure, before scheduled follow-up imaging. Thus 90 lesions (in 46 patients) were followed up with imaging studies. Lesions that were unchanged or reduced in size were considered to be under control. The 6-month actuarial lesion control rate was 88%. Smaller lesions (< 1 cm(3)) had a statistically improved likelihood of complete imaging response (loss of all contrast-enhancement p = 0.01). CONCLUSIONS: Image-guided radiosurgical treatment of brain metastases resulted in high rates of tumor control comparable to control rates reported for frame-based methods. High control rates were seen for small lesions in which spatial precision in dose delivery is critical. These data suggests that in regard to lesion control, IGRS using Novalis with ExacTrac is equivalent to frame-based radiosurgery methods.

Comparison of early complications for patients with convexity and parasagittal meningiomas treated with either stereotactic radiosurgery or fractionated stereotactic radiotherapy.

OBJECTIVE: Patients with convexity and parasagittal (CPS) meningiomas treated with stereotactic radiosurgery (SRS) have been shown to be at risk for posttreatment symptomatic peritumoral edema (SPTE). We sought to analyze the pattern of this complication and compare it with the SPTE experienced in our patients treated with fractionated stereotactic radiotherapy. METHODS: From January 2003 to October 2005, 32 patients with CPS meningiomas were treated. Thirty patients with a total of 38 lesions had sufficient follow-up for analysis. Group A (n = 14) patients were treated with single fraction SRS, and Group B (n = 16) patients were treated with fractionated stereotactic radiotherapy. The lesion volume was different between the two groups with the Group B median volume (7.46 cm) being larger than that for Group A (2.84 cm) (P = 0.0008). Conversely age, follow-up, sex, prior surgical events, number of lesions, tumor location, and atypical histology did not differ between these groups. The median marginal dose for patients in Group A was 14 Gy (range, 12.5-18 Gy). For Group B, six patients received a median marginal dose of 50.4 Gy in 28 fractions, and 10 patients received a marginal dose of 25 Gy in five fractions. RESULTS: Seven of the 30 patients treated in this series developed posttreatment SPTE. The incidence of SPTE in Group A (six of 14 patients) was significantly higher than that in Group B (one of 16 patients) (P = 0.031). The median time to onset of SPTE in the six patients in Group A was 4 months. In Group B, one patient had onset of SPTE in 3 months. On univariate analysis, larger tumor volume (P = 0.0014) and tumor margin dose >14 Gy in patients undergoing SRS (P = 0.031) was associated with onset of SPTE. Age, previous surgery, and tumor location were not associated with onset of SPTE. CONCLUSION: Despite larger lesion volumes, fractionated stereotactic radiotherapy is associated with less risk of posttreatment SPTE than SRS for patients with CPS meningiomas in our series. For patients treated with SRS, smaller volume and dose <14 Gy seems to be safe. Longer follow-up will be required to compare late complications and tumor control rates in these patients.

Prognostic factors for radiosurgery treatment of trigeminal neuralgia.

OBJECTIVE: Trigeminal neuralgia treatment results are thought to be highly dependent upon selection criteria. We retrospectively analyzed a series of patients to determine the likelihood of treatment success for patients treated with radiosurgery. METHODS: A retrospective analysis of 82 patients treated with linear accelerator radiosurgery was undertaken with a median follow-up period of 18 months. Patients were evaluated with a standard inventory using the Barrow Neurological Institute pain scale as the primary means of outcome measurement. Patients were treated with a linear accelerator using a single isocenter plan delivered via a 4-mm collimator, typically with seven noncoplanar arcs to a peak dose of 85 or 90 Gy in primary treatments and 60 Gy in retreatments. The primary target was the cisternal component of the trigeminal nerve. Posttreatment outcomes were analyzed in light of pretreatment patient characteristics, including age, sex, anticonvulsant responsiveness, quality and pattern of pain, length of disease, number of previous procedures, and radiation dose exposure to the root entry zone. Univariate analysis and multivariate logistic regression analysis were used to determine the prognostic significance of various pretreatment variables. RESULTS: Good results as defined by a Barrow Neurological Institute outcome score of IIIb or better were seen in 85.3% of patients. Excellent results as defined by a Barrow Neurological Institute outcome score of I were seen in 49% of patients. The median time to satisfactory improvement of pain was 4 weeks. Only one variable, sensitivity to anticonvulsant medication, was found to be statistically significant in both univariate (P = 0.003) and multivariate analysis (P = 0.025). All other variables analyzed failed to reach statistical significance. Complications were not common, with seven patients (8.5%) developing new-onset hypoesthesia and two patients (2%) developing dry eye symptoms. CONCLUSION: Anticonvulsant responsiveness is the single most important prognostic indicator of treatment success for patients presenting with facial pain. Other predictive factors generally failed to reach statistical significance. Linear accelerator radiosurgery for trigeminal neuralgia is a safe and effective treatment for well-selected patients, with results similar to those obtained with gamma unit radiosurgery.

Contemporary methods of radiosurgery treatment with the Novalis linear accelerator system.

Radiosurgery has emerged as an indispensable component of the multidisciplinary approach to neoplastic, functional, and vascular diseases of the central nervous system. In recent years, a number of newly developed integrated systems have been introduced for radiosurgery and fractionated stereotactic radiotherapy treatments. These modern systems extend the flexibility of radiosurgical treatment in allowing the use of frameless image-guided radiation delivery as well as high-precision fractionated treatments. The Novalis linear accelerator system demonstrates adequate precision and reliability for cranial and extracranial radiosurgery, including functional treatments utilizing either frame-based or frameless image-guided methods.

Breast conserving surgery and accelerated partial breast irradiation using the MammoSite system: initial clinical experience.

HYPOTHESIS: Balloon catheter-based accelerated partial breast irradiation (APBI) may result in desirable short-term outcomes in patients undergoing breast conserving surgery. DESIGN: Prospective consecutive case series. SETTING: Tertiary multidisciplinary referral center. PATIENTS: Forty selected patients with invasive breast carcinoma undergoing breast conserving surgery and MammoSite device placement. INTERVENTIONS: Breast conserving surgery, sentinel and/or axillary node dissection, placement of the new balloon catheter applicator (MammoSite device), and APBI. MAIN OUTCOME MEASURES: Infection, early and late seroma, device explantation, time to initiating APBI, acute toxic effects on the skin, and cosmesis using the Harvard Scale. RESULTS: Thirty-nine patients underwent MammoSite device placement at the time of lumpectomy; 1 patient underwent percutaneous device placement after lumpectomy. Nineteen patients (49%) had drainage catheters placed in the breast cavity at the time of lumpectomy. Wound infection developed in 3 patients (8%). Five devices (12%) were explanted because of unfavorable final pathological findings or infection. The mean time to the start of APBI in patients who did not undergo simultaneous drain placement was 7.2 days (range, 5-12 days), compared with 5.1 days (range, 3-8 days) in patients who did (P = .008). With a mean follow-up of 13.3 months (range, 2-28 months), patients completing APBI had limited toxic effects on the skin, with excellent or good cosmetic results in 39 patients (97%). CONCLUSIONS: Use of the MammoSite system in APBI has favorable short-term outcomes. Infection and radiation treatment delay are common and may warrant use of perioperative antibiotics and drain placement, respectively. A small number of patients who have device placement at the time of lumpectomy will require explantation because of unfavorable final pathological findings. Short-term outcomes of MammoSite brachytherapy support further studies comparing APBI with standard whole breast irradiation in patients undergoing breast conserving surgery.

Treatment of trigeminal neuralgia with linear accelerator radiosurgery: initial results.

OBJECT: Radiosurgery has emerged as an important treatment of trigeminal neuralgia. Substantial advantages have been demonstrated in safety and comfort over other modalities. Radiosurgical treatment of trigeminal neuralgia has been well investigated with gamma knife devices involving fixed cobalt sources. Few reports exist concerning trigeminal neuralgia treated using linear accelerator (LINAC)-based devices. In recent years these devices have reached the level of mechanical precision that is required for such functional treatments. The authors describe their initial experience with radiosurgical treatment of trigeminal neuralgia when using a BrainLAB Novalis LINAC device equipped with the commercially available 4-mm collimator. METHODS: A total of 32 patients were treated in a 12-month period between November 2002 and November 2003. The median patient age was 67 years (range 38-84 years). Facial pain was graded using the Barrow Neurological Institute (BNI) scoring system. All patients' pain was BNI Grade IV or V prior to treatment. Of these patients, 22 were undergoing initial treatment, and 10 were undergoing retreatment for recurrent pain following various treatments including percutaneous procedures, gamma knife surgery (GKS), or microvascular decompression. Two patients had multiple sclerosis. In patients undergoing initial radiosurgery, the most proximal segment of the cisternal portion of the trigeminal nerve received 85 to 90 Gy administered in a 5- or 7-noncoplanar arc single-isocenter plan with a 4-mm circular collimator. In patients undergoing repeated radiosurgery, the target received 60 Gy. Overall good and excellent results (BNI Grade I, II, or III) were achieved in 25 (78%) of 32 patients. The median time to pain relief was 6 weeks. Fair results (improvement in pain with BNI Grade IV) were achieved in three patients (9%), and poor results (no improvement in pain and BNI Grade IV or V) were seen in four (13%). Two patients demonstrated new trigeminal dysfunction following treatment. No other complications occurred. CONCLUSIONS: High-precision imaging and LINAC instrumentation have allowed for treatment of trigeminal neuralgia with results and safety comparable to those achieved using GKS. Linear accelerator-based radiosurgery with the Novalis device is a safe and effective method of managing trigeminal neuralgia and may become the preferred means at centers where the technology is available.

Geometrical accuracy of the Novalis stereotactic radiosurgery system for trigeminal neuralgia.

OBJECT: Stringent geometrical accuracy and precision are required in the stereotactic radiosurgical treatment of patients. Accurate targeting is especially important when treating a patient in a single fraction of a very high radiation dose (90 Gy) to a small target such as that used in the treatment of trigeminal neuralgia (3 to 4-mm diameter). The purpose of this study was to determine the inaccuracies in each step of the procedure including imaging, fusion, treatment planning, and finally the treatment. The authors implemented a detailed quality-assurance program. METHODS: Overall geometrical accuracy of the Novalis stereotactic system was evaluated using a Radionics Geometric Phantom Chamber. The phantom has several magnetic resonance (MR) and computerized tomography (CT) imaging-friendly objects of various shapes and sizes. Axial 1-mm-thick MR and CT images of the phantom were acquired using a T1-weighted three-dimensional spoiled gradient recalled pulse sequence and the CT scanning protocols used clinically in patients. The absolute errors due to MR image distortion, CT scan resolution, and the image fusion inaccuracies were measured knowing the exact physical dimensions of the objects in the phantom. The isocentric accuracy of the Novalis gantry and the patient support system was measured using the Winston-Lutz test. Because inaccuracies are cumulative, to calculate the system's overall spatial accuracy, the root mean square (RMS) of all the errors was calculated. To validate the accuracy of the technique, a 1.5-mm-diameter spherical marker taped on top of a radiochromic film was fixed parallel to the x-z plane of the stereotactic coordinate system inside the phantom. The marker was defined as a target on the CT images, and seven noncoplanar circular arcs were used to treat the target on the film. The calculated system RMS value was then correlated with the position of the target and the highest density on the radiochromic film. The mean spatial errors due to image fusion and MR imaging were 0.41+/-0.3 and 0.22+/-0.1 mm, respectively. Gantry and couch isocentricities were 0.3+/-0.1 and 0.6+/-0.15 mm, respectively. The system overall RMS values were 0.9 and 0.6 mm with and without the couch errors included, respectively (isocenter variations due to couch rotation are microadjusted between couch positions). The positional verification of the marker was within 0.7+/-0.1 mm of the highest optical density on the radiochromic film, correlating well with the system's overall RMS value. The overall mean system deviation was 0.32+/-0.42 mm. CONCLUSIONS: The highest spatial errors were caused by image fusion and gantry rotation. A comprehensive quality-assurance program was developed for the authors' stereotactic radiosurgery program that includes medical imaging, linear accelerator mechanical isocentricity, and treatment delivery. For a successful treatment of trigeminal neuralgia with a 4-mm cone, the overall RMS value of equal to or less than 1 mm must be guaranteed.