Single SRS Research Articles

Optimization of isocenter position for multiple brain metastases single-isocenter stereotactic radiosurgery to minimize dosimetric variations due to rotational uncertainty

PurposeThis paper studied a novel calculation framework that can determine the optimal value isocenter position of single isocenter SRS treatment plan for multiple brain metastases, in order to minimize the dosimetric variations caused by rotational uncertainty. Materials and methods21 patients with 2–4 GTVswho received SRS treatment for multiple brain metastases in our institution were selected for the retrospective study. The PTVwas obtained by expanding GTV 1 mm isotropic margin. We studied a stochastic optimization framework, which determined the optimal value isocenter location by maximizing the average target dose coverageCtarget,meanwith a rotation error of no more than 1°. We evaluated the performance of the optimal isocenter by comparing theCtarget,meanand average dice similarity coefficient (DSC)with the optimal value and the center of mass (CM) respectively as the treatment isocenter. The extra PTV margin to achieve 100% target dose coverage was calculated by our framework. ResultsCompared to the CM method, the optimal value isocenter method increased the averageCtarget,meanof all targets from 97.0% to 97.7%and the average DSC from 0.794to 0.799. Throughout all the cases, the average extra PTV margin to obtain full target dose coverage was 0.7 mmwhen using the optimal value isocenter as the treatment isocenter. ConclusionWe studied a novel computational framework using stochastic optimization to determine the optimal isocenter position of SRS treatment plan for multiple brain metastases. At the same time, our framework gave the extra PTV margin to obtain full target dose coverage.

PO-2048 Analysis of different optimization methods for single and multiple metastases SRS plans

PO-2048 Analysis of different optimization methods for single and multiple metastases SRS plans

RADT-04. SINGLE SESSION GAMMA KNIFE RADIOSURGERY TO TREAT PATIENTS WITH 20 OR MORE BRAIN METASTASES

Abstract BACKGROUND Stereotactic Radiosurgery (SRS) has become a primary management option for brain metastases (BMs). This present study aims to review outcomes in patients with ≥ 20 BMs treated in a single session SRS and to identify predictors of local tumor control (LTC) and overall survival (OS). METHODS We identified 75 patients including 26 non-small cell lung cancer (NSCLC), 21 small cell lung cancer (SCLC), 14 breast cancer (BC), and 14 melanoma patients who underwent SRS for ≥ 20 BMs between 2014 and 2020. The median number of tumors was 24 (range 20 – 52), and the median cumulative tumor volume was 3.70 cc (0.13 – 62.49 cc). The median margin dose was 16 Gy (14 – 20 Gy). Median skull integral dose was 5492 mJ (range 1372 – 11243 mJ). The median treatment time for each session was 160 min. Outcome variables were assessed using univariate and multivariate analyses with p < 0.05. RESULTS Median OS after SRS was 5.8 months (range 0.1 – 73.2 months). Primary cancer type and concurrent immunotherapy were significant predictive factors for patient OS after SRS (p = 0.01, 0.05, and 0.02, respectively). LTC rate at 6 and 12 months after SRS was 95.7% and 83.7%, respectively. Thirty (40.0%) patients underwent additional SRS and 3 patients (4%) received post-SRS WBRT due to distant tumor recurrence. The median time to distant recurrence was 5 months (range 2-28 months). SRS-induced adverse radiation effects (ARE) events were observed in 3 patients (4.0%; 1 NSCLC, 1 SCLC, and 1 melanoma). CONCLUSIONS Our results suggest that patients with ≥ 20 BMs can be safely treated with SRS with an excellent LTC rate and a low risk of ARE. Newly developed BMs can be treated with repeat SRS. This single-session SRS allows patients to proceed with systemic cancer care without interruption.

A Deep Learning-Based Computer Aided Detection (CAD) System for Difficult-to-Detect Brain Metastases (BM)

<h3>Purpose/Objective(s)</h3> After an initial course of SRS, new BMs are often identified in subsequent imaging, prompting additional SRS treatment. Upon review, many are already subtly evident (enhancing) on MRIs from the first SRS. We refer to these lesions as "retrospectively identified metastases" (RIMs). We sought to develop a CAD system that specifically excels at identifying small, subtle BMs that frequently go undetected by humans, by training a convolutional neural network (CNN) on a unique MRI dataset including many RIMs. <h3>Materials/Methods</h3> All patients with BMs treated with SRS alone at our institution from 2016 to 2018 were eligible, except those with prior brain-directed therapy or small cell histology. For patients who received two courses of SRS within 6 months, 3D axial post-contrast spoiled gradient recalled echo MRIs from the initial course were evaluated for RIMs. RIMs were categorized based on whether they met (+DC) or did not meet (-DC) diagnostic imaging-based criteria to classify them as metastases. Prospectively identified and treated metastases (PIMs) from these patients were also included, as were PIMs from patients who received a single SRS course and exhibited no "new" metastases for at least one year post SRS. Patients were randomized into 5 groups: 4 training/validation, 1 test. A modified open-source CNN, DeepMedic (DM), was optimized and trained using data augmentation and 4-fold cross-validation. Our final CAD solution employs ensembling, discrimination via a 3D conditional random field algorithm, and thresholding strategies. CAD performance was evaluated on the test set. <h3>Results</h3> 135 patients with 563 metastases were included: 72 RIMs (45 +DC, 27 -DC) and 491 PIMs, with median diameters of 2.7mm (0.9, 11.0) and 6.7mm (0.9, 37.9), respectively. CAD results are summarized in Table 1. High sensitivity was achieved for all prospectively-treatable BMs (PIMs and +DC RIMs): 93% overall, 79% < 3mm. 80% of all +DC RIMs were identified. A median of only 2 false positives were generated per patient, and the mean Dice similarity coefficient was 0.79. <h3>Conclusion</h3> A novel BM CAD system has been developed and trained using a unique MRI dataset including many RIMs. The algorithm demonstrates excellent sensitivity, even for RIMs, along with high specificity. These results outperform published works, especially for small BMs < 3mm. Study limitations include the modest number of patients from a single institution, retrospective nature, and selective inclusion criteria. Prospective, multi-institutional validation of the approach is warranted.

Phase II Clinical Trial of Image-Guided Cognitive-Sparing SRS in Patients With Brain Metastases

SRS for brain metastases is associated with a high rate (52%-64%) of cognitive deterioration. We performed a phase II clinical trial of critical white matter and hippocampal sparing brain SRS in patients with limited brain metastases, to improve cognitive preservation. We present feasibility of this approach and interim results.Adult patients with limited volume (< 10cc) brain metastases were enrolled on this single institution clinical trial from 2018-2021. Inclusion criteria include: age ≥ 18, expected life expectancy > 6 months, pathologic confirmation of malignancy. Prior WBRT was exclusionary. High resolution volumetric MRI with diffusion tensor imaging was performed pre-SRS and at 1-, 3- and 6-months post SRS. Regions of interest (ROIs) were segmented using robust, automated atlas-based tractography and hippocampal (HC) parcellation methods. 20 white matter (WM) tracts critical for cognitive functioning and fine motor skills, and the HC were designated as ROIs to spare during SRS planning. Knowledge-based SRS planning was employed, and all attempts were made to achieve ROI dose constraints without sacrificing target coverage or other OAR doses. Single fraction max dose constraints were 12 Gy for WM/8.4 Gy for HC (iso-effective doses used for 3 and 5 fraction SRS). A well-validated battery of neurocognitive (NCA) tests, including verbal memory and language, was performed pre and 3 months post SRS. Raw scores were converted to t-scores adjusting for age, sex, and years of education. Decline was considered > 1 standard deviation drop.Median age of cohort (n = 31) was 66 years and 58% were female. Most common primary was NSCLC (39%) or melanoma (23%), and 90% of patients had 1-3 brain metastases. Prescription doses ranged from 21-30 Gy in 1-5 fractions; 10 patients were treated with both single and multi-fraction SRS to different targets. Max dose constraints for ROIs were met on 69% of SRS plans. Across plans, constraints were met for 98% of 595 WM tracts and 97% of 64 HC treated. At 6 months post SRS there were no local failures. To date (median follow up: 6 months), 5 patients have died from systemic disease progression and 1 patient from distant brain disease progression. For patients in whom pre and 3-month NCA scores were available (n = 13), 97% of WM ROIs and 100% of HC ROIs met study constraints. At 3 months, 74% of patients had no decline on HVLT total/delayed recall memory tests. Similarly, 93% and 89% showed no decline on BNT and DKEFS letter fluency language tests, respectively. There was no significant change in NCA test scores in the cohort from pre to 3 months post SRS (paired t-test, P-values > 0.05).Critical WM and HC sparing brain SRS using automated segmentation/planning tools is achievable and feasible, though can depend on proximity to targets. Sparing these critical structures may improve cognitive preservation in domains such as verbal memory and language.S. Unnikrishnan: None. R. Karunamuni: None. G. Kim: None. M. Connor: None. M.A. Salans: None. P. Sanghvi: Speaker's Bureau; Varian, VisionRT.A. Bruggeman: Research Grant; American Society of Clinical Oncology. D.R. Simpson: None. J. Yu: None. A. Reyes: None. A. Stasenko: None. K.L. Moore: Research Grant; Varian Medical Systems Inc. Honoraria; Varian Medical Systems Inc. Travel Expenses; Varian Medical Systems Inc. V. Moiseenko: None. C. McDonald: Research Grant; GE.J.A. Hattangadi-Gluth: Research Grant; NIH/NCI. Honoraria; Varian Medical Systems. Consultant; Varian Medical Systems. Site PI for cooperative group trials at UCSD for CNS; Site-PI; NCCN.

Single isocenter SRS using CAVMAT offers improved robustness to commissioning and treatment delivery uncertainty compared to VMAT.

PurposeIn this study, we evaluate and compare single isocenter multiple target VMAT (SIMT) and Conformal Arc Informed VMAT (CAVMAT) radiosurgery's sensitivity to uncertainties in dosimetric leaf gap (DLG) and treatment delivery. CAVMAT is a novel planning technique that uses multiple target conformal arcs as the starting point for limited inverse VMAT optimization.MethodsAll VMAT and CAVMAT plans were recalculated with DLG values of 0.4, 0.8, and 1.2 mm. DLG effect on V6Gy[cc], V12Gy[cc], and V16Gy[cc], and target dose was evaluated. Plans were delivered to a Delta4 (ScandiDos, Madison, WI) phantom and gamma analysis performed with varying criteria. Log file analysis was performed to evaluate MLC positional error. Sixteen targets were delivered to a SRS MapCHECK (Sun Nuclear Corp., Melbourne, FL) to evaluate VMAT and CAVMAT's dose difference (DD) as a function of DLG.ResultsVMAT's average maximum and minimum target dose sensitivity to DLG was 9.08 ±3.50%/mm and 9.50 ± 3.30%/mm, compared to 3.20 ± 1.60%/mm and 4.72 ± 1.60%/mm for CAVMAT. For VMAT, V6Gy[cc], V12Gy[cc], and V16Gy[cc] sensitivity was 35.83 ± 9.50%/mm, 34.12 ± 6.60%/mm, and 39.23 ± 8.40%/mm. In comparison, CAVMAT's sensitivity was 23.19 ± 4.50%/mm, 22.45 ± 4.40%/mm, and 24.88 ± 4.90%/mm, respectively. Upon delivery to the Delta4, CAVMAT offered superior dose agreement compared to VMAT. For a 1%/1 mm gamma analysis, VMAT and CAVMAT had a passing rate of 94.53 ± 4.40% and 99.28 ± 1.70%, respectively. CAVMAT was more robust to DLG variation, with the SRS MapCHECK plans yielding an absolute average DD sensitivity of 2.99 ± 1.30%/mm compared to 5.07 ± 1.10%/mm for VMAT. Log files demonstrated minimal differences in MLC positional error for both techniques.ConclusionsCAVMAT remains robust to delivery uncertainties while offering a target dose sensitivity to DLG less than half that of VMAT, and 65% of that of VMAT for V6Gy[cc], V12Gy[cc], and V16Gy[cc]. The superior dose agreement and reduced sensitivity of CAVMAT to DLG uncertainties indicate promise as a robust alternative to VMAT for SIMT SRS.

134. Variability in SRS 22r outcome measures in non- and operatively treated patients with adolescent idiopathic scoliosis (AIS) greater than 40°

BACKGROUND CONTEXT The SRS 22r outcome score is a highly-utilized and validated measure to gauge success in the treatment of patients with adolescent idiopathic scoliosis (AIS). The reliability of measurements in a single patient across time has not been studied. PURPOSE This study examined the variability in SRS 22r scores for both operatively (O) and nonoperatively (NO) managed patients with AIS. We hypothesized that SRS 22r scores would demonstrate high variability over time in AIS patients with curves 40°or greater in both operatively and nonoperatively treated patients. STUDY DESIGN/SETTING This was a prospective, observational study. PATIENT SAMPLE AIS patients with curves measuring at least 40° were followed prospectively with SRS 22r scores. Only patients with 3 or more separate SRS scores were included (average 4, range 3-8 for both groups). For O patients, only scores collected one year or longer postoperatively were analyzed. There were 193 NO patients and 102 O patients. OUTCOME MEASURES We examined variability in SRS 22r scores as determined by Intraclass Correlation Coefficient (ICC) and Standard Deviation (SD) for individual patients, and as groups, for O and NO patients. METHODS SRS 22r SDs were compared to published MCIDs for all SRS 22r subdomain scores. RESULTS Average age at last score was 19.9 years for NO and 20.6 years for O patients. Average time between 1st and last score was 3.2 and 4.3 years, respectively. Average Cobb angle at last follow-up was 52° for NO and 29° for O patients. ICCs were found to be only fair to poor in all subdomains and for total scores in both groups. The majority of patients in both groups had SRS 22r subdomain score standard deviation that exceeded literature reported MCID for these domains. CONCLUSIONS The SRS 22r outcome measure demonstrated unacceptably high variability in all domains for both groups of AIS patients by ICC analysis. The SD of SRS 22r subdomain scores in most patients exceeds published MCID values calling into question the usefulness of a single SRS 22r subdomain score for both research and clinical decision purposes. Distribution based MCID total raw scores also frequently exceed MCID values. Surgeons should exercise caution in drawing conclusions concerning patient-reported outcomes of treatment based on a single SRS 22r subdomain or total score. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. The SRS 22r outcome score is a highly-utilized and validated measure to gauge success in the treatment of patients with adolescent idiopathic scoliosis (AIS). The reliability of measurements in a single patient across time has not been studied. This study examined the variability in SRS 22r scores for both operatively (O) and nonoperatively (NO) managed patients with AIS. We hypothesized that SRS 22r scores would demonstrate high variability over time in AIS patients with curves 40°or greater in both operatively and nonoperatively treated patients. This was a prospective, observational study. AIS patients with curves measuring at least 40° were followed prospectively with SRS 22r scores. Only patients with 3 or more separate SRS scores were included (average 4, range 3-8 for both groups). For O patients, only scores collected one year or longer postoperatively were analyzed. There were 193 NO patients and 102 O patients. We examined variability in SRS 22r scores as determined by Intraclass Correlation Coefficient (ICC) and Standard Deviation (SD) for individual patients, and as groups, for O and NO patients. SRS 22r SDs were compared to published MCIDs for all SRS 22r subdomain scores. Average age at last score was 19.9 years for NO and 20.6 years for O patients. Average time between 1st and last score was 3.2 and 4.3 years, respectively. Average Cobb angle at last follow-up was 52° for NO and 29° for O patients. ICCs were found to be only fair to poor in all subdomains and for total scores in both groups. The majority of patients in both groups had SRS 22r subdomain score standard deviation that exceeded literature reported MCID for these domains. The SRS 22r outcome measure demonstrated unacceptably high variability in all domains for both groups of AIS patients by ICC analysis. The SD of SRS 22r subdomain scores in most patients exceeds published MCID values calling into question the usefulness of a single SRS 22r subdomain score for both research and clinical decision purposes. Distribution based MCID total raw scores also frequently exceed MCID values. Surgeons should exercise caution in drawing conclusions concerning patient-reported outcomes of treatment based on a single SRS 22r subdomain or total score.

Results of a Third or Fourth Radiosurgery for Trigeminal Neuralgia

Stereotactic Radiosurgery SRS is an accepted option for treatment of medically refractory trigeminal neuralgia (TN) with a median duration of pain relief of 5 years. Repeat SRS for recurrent pain has been well described with similar results. Data regarding the use of a third or fourth SRS for recurrent pain are limited. Here we report the largest series to date on the use of a third or fourth SRS for TN. Retrospective review of a single institution SRS database identified 24 cases of unilateral TN in 23 patients who were treated with 3 sessions of SRS from 1999 to 2018. 3 patients underwent a fourth SRS. Background history, treatment outcomes and toxicity, and dosimetric data were obtained by chart review and telephone interview. Pain relief was defined using the Barrow Neurological Institute (BNI) scale. Categorical variables were compared using the chi square or Fisher’s exact test. Duration of at least BNI IIIB pain relief was estimated using the Kaplan-Meier method and compared with the log-rank test. Univariate cox proportional hazards were used to evaluate for predictors of pain relief. 22 of 24 cases had sufficient follow up to determine BNI pain outcomes. 18 of the 22 cases (82%) achieved at least BNI IIIb pain relief. At a median follow up of 1.96 years, the median duration of at least BNI IIIb pain relief after third SRS was 3.90 years, with 1, 3, and 5 year pain relief rates of 59%, 51%, and 38% respectively. New or worsening facial numbness was seen in 9 cases (41%) with 1 (4.5%) being reported as bothersome. 1 case (4.5%) of corneal abrasions requiring surgery and 2 cases (9%) of dry eye without vision loss or corneal abrasions, and 0 cases of anesthesia dolorosa were reported. The median dose at third SRS was 75 Gy (range 75-85). All 3 patients treated with a fourth SRS had at least BNI IIIb pain relief with no relapse at a median follow up of 2.54 years. No cases of severe numbness or toxicity were reported after fourth SRS. No factors predicting initial response to a third SRS were identified. Patients with a successful second SRS were less likely to experience pain relapse after third SRS (HR 0.12, p = .02). Third and fourth SRS had a longer durability of pain relief than first and second SRS (p = .02). No factors predictive of numbness after third SRS were identified. Non-numbness toxicity after third SRS was associated with a higher dose to the pons surface (median 41.6 Gy vs 16.9 Gy, p < .01) and decreased distance from the isocenter to the pons surface (median 2.9 mm vs 4.6 mm, p < .01). A third or fourth SRS is an effective treatment option for recurrent TN and may be more durable than the first or second SRS. Durable relief is more likely in patients with a successful second SRS. Toxicity rates appear to increase with third SRS, and dose to the pons should be limited to decrease this risk. The views expressed in this article are those of the author and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the U.S. Government.

RADI-28. UP-FRONT SINGLE SESSION RADIOSURGERY FOR LARGE BRAIN METASTASES - VOLUMETRIC RESPONSES AND OUTCOMES

OBJECTIVE: Patients presenting with large brain metastases (LBM), described in the literature as ≥2.5 cm in maximum diameter or ≥10cm3in volume, pose a management challenge. For patients not compromised by mass effect, corticosteroid therapy followed by SRS allows for efficient, minimal access care that facilitates immediate institution of systemic therapy. METHODS: We performed a volumetric-based analysis in order to determine the efficacy of single-session SRS in the treatment of LBM in comparison to other treatment modalities. Thirty patients over the age of 18 with systemic cancer and brain metastases (≥2.7cm in greatest diameter or ≥10cm3in volume) who underwent single session SRS were included. Serial tumor volumes, clinical outcomes, and medication requirements were studied. RESULTS: Among 30 patients, 70% of patients had either lung, melanoma, or breast cancer. Median initial tumor size (maximum diameter) was 32mm (range 28–43) and median initial tumor volume was 9.32cm3 (range 1.09–25.31). Median marginal dose was 16Gy (range 12–18). Average percent decrease in tumor volume was 50% on imaging at 4–8 weeks, 60% at 4–6 months, 48% at 6–8 months, and 67% at >8 months compared to initial imaging. Only one patient required a subsequent craniotomy 4 years after SRS for an enlarging cyst which was granulation tissue consistent with radiation effects on pathology. There were no adverse events immediately following SRS. Median corticosteroid use after SRS was 21 days. There was no statistically significant difference in KPS score between treatment day and last follow up, suggesting relative safety and maintenance of function. CONCLUSION: Initial high dose corticosteroid therapy followed by prompt single session SRS is a safe and efficacious method of managing patients with large brain metastases (defined in our study as ≥2.7cm or ≥10cm3), if the clinical condition of the patient is acceptable at presentation.

EP-2202: Accuracy of and quality assurance for VMAT-based, single isocenter SRS for multiple targets

EP-2202: Accuracy of and quality assurance for VMAT-based, single isocenter SRS for multiple targets

SU-F-T-596: Single Isocenter SRS Plan QA for Multiple Brain Lesion Cases

Purpose: Linac-based single isocenter SRS treatments for multiple brain lesions have been developed in recent years. However, it is a challenge to perform patient specific plan QA in cases where a large number of small and widely spread-out lesions are involved. We have developed a method to measure all target dose distributions in a single planar measurement. Methods: Varian Eclipse TPS was used to create dynamic conformal arc or RapidArc© plans. Verification plans are created with a fixed gantry angle, and planar projections of 3D dose distributions are created which show high dose regions correlated to each individual lesion. Two techniques were employed for dose measurements: an actual treatment plan delivered with a phantom mounted on the gantry; and/or a verification QA plan with a phantom placed on the couch. Gafchromic films and RIT© software were used for dosimetric analysis. A high dose region was selected for absolute dose measurements. Results: Test plans with up to 10 targets were performed with satisfactory results in the commissioning of this method. For clinical cases, we performed QA on plans with lesion number range from 2 to 7 and size from 0.5 to 3 cm. The absolute dose measurement for dynamic conformal arc plans is within 5% for target > 1 cm and 7% for target ≤1.0 cm. Gamma analyses were performed for whole area covered as well as each focused high-dose region corresponding to individual lesions. The pass criteria is 90% or higher for 3% and 1 mm. Each plan QA took about 1–2 hrs to complete. Conclusion: Our single isocenter SRS QA method has proven to be practical. The process is capable of capturing and analyzing multiple high dose regions in a single planar measurement. It takes reasonable time to verify each individual target without sacrificing accuracy and clinical relevance.

RTRB-11MULTIPLE BRAIN METASTASES TREATED WITH SINGLE-ISOCENTER LINAC-BASED STEREOTACTIC RADIOSURGERY (SRS)

SRS has been widely employed for treating multiple brain lesions using various techniques with multiple isocenters. A disadvantage of this approach is the prolonged treatment time, which is proportional to the number of lesions. Prolonged treatment time may lead to patient discomfort and movement with attendant risk of undertreating the lesion and increasing dose to normal brain tissue. To shorten treatment time, we and others have moved to a single iso-center approach, which enables parallel irradiation of multiple lesions instead of the conventional serial approach. The aim of this study is to evaluate the clinical results of this treatment approach. Between November-2010 and May-2014 we treated 162 patients with 2 or more lesions (2-5) with a single isocenter SRS approach. Pathologies treated included non-small cell lung cancer, breast cancer, colo-rectal cancer and melanoma, 46%, 22%, 10.7% and 8.7%, respectively. Patients were RPA class I (41.3%), II (26.7%), III (32.0%). Treatment plans were created using ERGO ++ (Elekta, Sweden) planning software or Eclipse™ (Varian, USA) planning software to create inverse intensity-modulated arc therapy (VMAT). Treatments were performed using Synergy-S micro-leaf beam modulator with 4mm leaves, or TruebeamSTx- Novalis with 2.5mm microleaf collimator in the center and 5mm in the periphery. Plans were created using single isocenter with fixed beams, static arcs and/or combination of the both with manual modification of the leave configuration to accommodate the shape and position of the lesions or VMAT plans consistent of 3-4 dynamic arcs. Median survival for RPA I, II, and III was 13.3 months (10.9-17.5), 6.48 months (4.9-8.7) and 4.6 months (3.9-5.5), respectively on Kaplan Meier Survival Analysis. Our initial results suggest that single-isocenter plans can be utilized to deliver conformity equivalent to that of multiple isocenter techniques and efficiently delivered requiring less than half the beam time required for multiple isocenter set ups.

Stereotactic Radiosurgery with Neoadjuvant Embolization of Larger Arteriovenous Malformations: An Institutional Experience

Objective. This study investigates the safety and efficacy of a multimodality approach combining staged endovascular embolizations with subsequent SRS for the management of larger AVMs. Methods. Ninety-five patients with larger AVMs were treated with staged endovascular embolization followed by SRS between 1996 and 2011. Results. The median volume of AVM in this series was 28 cm3 and 47 patients (48%) were Spetzler-Martin grade IV or V. Twenty-seven patients initially presented with hemorrhage. Sixty-one patients underwent multiple embolizations while a single SRS session was performed in 64 patients. The median follow-up after SRS session was 32 months (range 9–136 months). Overall procedural complications occurred in 14 patients. There were 13 minor neurologic complications and 1 major complication (due to embolization) while four patients had posttreatment hemorrhage. Thirty-eight patients (40%) were cured radiographically. The postradiosurgery actuarial rate of obliteration was 45% at 5 years, 56% at 7 years, and 63% at 10 years. In multivariate analysis, larger AVM size, deep venous drainage, and the increasing number of embolization/SRS sessions were negative predictors of obliteration. The number of embolizations correlated positively with the number of stereotactic radiosurgeries (P < 0.005). Conclusions. Multimodality endovascular and radiosurgical approach is an efficacious treatment strategy for large AVM.

Stereotactic radiosurgery for central neurocytoma: a quantitative systematic review

Central neurocytoma was originally described as a rare benign neuronal tumor. However, progression and local recurrences after surgery are well recognized. Stereotactic radiosurgery is another option for treatment of CN. In order to evaluate the efficacy of SRS, we performed a quantitative systematic review of the available data on SRS for CN. To identify eligible studies, systematic searches for all CNs treated with SRS were conducted in major scientific publication databases. English studies published prior to May 2011 were reviewed and summarized with reference to the inclusion and exclusion criteria. Tumor local control was analyzed. Heterogeneity and publication bias were assessed, and the summary control rate and 95%confidence interval (CI) were calculated from the raw data.Of 35 eligible studies, five with a total of 64 CNs were included in this quantitative analysis. Four studies reported a mean or median follow-up time of[60 months. The test of heterogeneity was non-significant among the included studies. Publication bias was observed as indicated by an asymmetric funnel plot. There was non-significance in Begg’s test and Egger’s test. The estimated cumulative rate of neuro-imaging tumor control was 91.1% (95%CI = 80.2–96.3%) at a mean follow-up of 59.3 months(range 6–140 months). The P-value was\0.0001 under a random-effect model. Sensitivity analysis showed a similar summary control rates (89.5–93.7%). Based on the summary local control rate of SRS for CN found in this quantitative analysis, we suggest that single session SRS is an effective and safe alternative therapy for recurrent or residual CN. However, the results of our analysis are limited by the predominance of case series studies due to scarcity of published research. Further randomized trials of CN patients via multicenter consortia should be considered for supplementing the weak points in our quantitative analysis.

Gas source molecular beam epitaxy growth of SrS:Ce for flat panel displays

SrS:Ce thin films have been grown by gas source molecular beam epitaxy (GSMBE). The growth conditions have been systematically investigated as a function of growth temperature, sulfur to strontium flux ratio, and cerium flux. Single crystal SrS and high quality SrS:Ce were successfully grown on GaAs and glass substrates, respectively, without post-annealing process at temperature as low as 600°C. It was found that the electroluminescence (EL) performance was greatly improved by addition of ZnS during the growth.

Experiments and simulations of tunnel-ionized plasmas.

The tunneling-ionization model predicts that fully ionized plasmas with controllable perpendicular ({ital T}{sub {perpendicular}}) and negligible longitudinal temperature ({ital T}{sub {parallel}}) can be produced. The validity of these predictions has been studied through experiments and supporting theory and simulations. Emission of odd harmonics of the laser frequency, indicative of a stepwise ionization process, has been observed. X-ray measurements show that the plasma temperature is higher for a circularly polarized laser-produced plasma compared to when linear polarization is used. Analytically we find that the growth of the stimulated Raman (SRS) and Compton scattering (SCS) instabilities are suppressed during the ionization phase. A higher {ital T}{sub {parallel}} than expected from the single-particle-tunneling model was observed after the ionization phase through SCS fluctuation spectra. The maximum achievable plasma density is found to be limited by ionization induced refraction. One-dimensional (1D) simulations show that, after the ionization phase, the initial {ital T}{sub {parallel}} is low as expected from the single particle model and SRS density fluctuations grow to large values. In 2D simulations, however, {ital T}{sub {parallel}} at the end of the ionization phase is already much higher and only SCS is seen to grow. The simulations indicate that stochastic heating and the Weibelmore » instability play an important role in plasma heating in all directions and in making the plasma isotropic. Two-dimensional simulations also confirm that refraction plays a crucial role in determining the maximum electron density that can be obtained in such plasmas.« less