Linac Radiosurgery Research Articles

The beginning of linac radiosurgery at the JCRT.

Medical PhysicsAccepted Articles REVIEW ARTICLE The Beginning of Linac Radiosurgery at the JCRT Wendell R. Lutz, Corresponding Author Wendell R. Lutz lutzwendell@yahoo.com University of Arizona Cancer Center Email: lutzwendell@yahoo.comSearch for more papers by this author Wendell R. Lutz, Corresponding Author Wendell R. Lutz lutzwendell@yahoo.com University of Arizona Cancer Center Email: lutzwendell@yahoo.comSearch for more papers by this author First published: 22 February 2023 https://doi.org/10.1002/mp.16276 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as https://doi.org/10.1002/mp.16276 AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Accepted ArticlesAccepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future. RelatedInformation

528 Robotic Image-Guided LINAC Radiosurgery for Trigeminal Neuralgia: Results After 10 Years

INTRODUCTION: Frameless image-guided robotic radiosurgery delivering 60 Gy to a 6mm mid-cisternal/retrogasserian segment of the affected trigeminal nerve was used to treat 702 patients affected by severe Trigeminal Neuralgia(TN) refractory to medications . Clinical outcomes in 92 patients with minimum follow-up of 10 years are here reported. METHODS: 702 patients with severe, long-standing TN refractory to medications have been treated at the Cyberknife Center of CDI,Milan,Italy over the last 13 years. A dedicated protocol for imaging ( head CT with and without contrast, slice thickness 0,5 mm; brain MR including MPRAGE and CISS/FIESTA sequences) and treatment( selecting a 6 mm segment of the nerve going from the midcisternal toward the retrogasserian region with a dose prescription of 60Gy @80% isodose) was employed. Regular clinical follow-up was performed one or more times per year according to clinical needs and distance from the treatment. Recurrent pain was treated with the same protocol( a lower dose of 45 Gy was later selected for retreatments). RESULTS: Pain control rates of 92%,87%,76%,74% after respectively 1,2, 3 and 5 years have been found. 92 patients with follow-up longer than 10 years show pain control rate of 72% while the rate of persistent bothering parethesias is 5, 4% (5 patients). No other neurological complications have been found. CONCLUSIONS: Long-term follow-up shows that frameless Linac radiosurgery provides long-term pain control in over 2/3 of the treated patients, with low rate of sensory complications and no other neurological complications.

Stereotactic radiosurgery for limited brain metastasis using three different techniques: helical tomotherapy, volumetric modulated arc therapy, and cone-based LINAC radiosurgery.

Specific radiation delivered to tumors by stereotactic radiosurgery (SRS) has become widely used in the treatment of brain metastasis. This study aimed to compare radiation therapy planning and its parameters from SRS using three different modalities: helical tomotherapy (HT), volumetric modulated arc therapy (VMAT), and cone-based linac radiosurgery (Cone-based). Each contouring dataset of patents who experienced one to four brain metastasis received SRS in our center was re-planned to create radiation therapy planning in all three treatment systems (HT, VMAT, and Cone-based). The parameters of conformity index (CI), homogeneity index (HI), CI50, and gradient index (CGI) were analyzed to compare the effects of the three techniques. Decision score analysis was used to evaluate the performance on dosimetric and organs-at-risk parameters among the different techniques by applying the Cone-based technique as a benchmark. A total of 21 patients with 39 lesions were included in this study. The results from the decision score analysis demonstrated statistically identical CI, CI50, and CGI values between Cone-based and VMAT for single lesions. For multiple lesions, VMAT also provided better CI when compared to Cone-based technique while HT exhibited the poorest dosimetric parameters. Moreover, VMAT exhibited the lowest BrainV5Gy value and displayed the shortest beam-on time calculation. We have conducted a comprehensive comparison of SRS planning approaches. The Cone-based technique revealed the highest HI value, while VMAT provided the best estimated beam-on time value. HT displayed a feasible SRS modality for single lesions, but not for multiple lesions.

Dosimetric comparison of volumetric modulated arc therapy with TrueBeam LINAC and hypofractionated radiosurgery with gamma knife ICON for large (>10 cm3) skull base meningiomas.

Multi Fractionated stereotactic radiosurgery (MF-SRS) of Linac has an essential role in the treatment of skull base meningiomas (sbMNG). However, Gamma Knife Icon (GK) allows MF-SRS using mask immobilization with onboard image guidance. This dosimetric study aims to investigate whether equivalent plan quality can be achieved with Volumetric Modulated Arc Therapy (VMAT) in patients with large sbMNG (>10 cm3) previously treated with GK. Twenty patients with the median target volume of 19.7cm3 are re-planned by using VMAT with 20 Gy in 5 fractions. Plan qualities are compared to tumor coverage, paddick conformity index (PCI), gradient index (GI), V4 Gy, V10 Gy, V12 Gy, optic chiasm V20 Gy, brainstem V23 Gy, optic nerve V25 Gy volumes, and maximum doses for all. Additionally, beam-on time and approximate planning time are also analyzed and compared. All plans provide adequate clinical requirements. First, the CI is comparable for the GK and VMAT (0.99±0.01 vs. 1.13±0.20; p = 0.18). Second, VMAT has a significantly higher GI than GK (3.81±0.35 vs. 2.63±0.09; p < 0.001). Third, the PCI is significantly higher in GK than VMAT (0.76±0.05 vs. 0.70±0.07; p < 0.001). The lower GI of the GK also results in significantly lower V4 Gy (156.1±43.8 vs. 207.5±40.1 cm3, p < 0.001) and V10 Gy (26.1±9.0 vs. 28.9±7.7 cm3, p < 0.001) compared to VMAT. Last, the VMAT reduces beam-on time (4.8±0.5 vs. 19±1.1 min.; p < 0.001). Although both systems have succeeded in creating effective plans in clinical practice, the GK reveals more effective lower normal brain tissue doses. However, the shorter treatment time with LINAC, excluding the total procedure time, can be considered advantageous over GK.

Use of High Definition Multileaf Colimator for the Treatment of Trigeminal Neuralgia

In the present work, a treatment technique for trigeminal neuralgia (TN) using LINAC radiosurgery is shown. The technique is based on the optimization of ten static arcs in such a way as to minimize the overlapping of the treatment fields with the brainstem. We will call this technique brainstem-optimized (BO). The results are compared with another technique described in the literature known as a virtual cone (VC). The comparison of dosimetry results that have been carried out essentially shows that the doses in the brainstem V12Gy-brainstem, D0.5cm3-brainstem and D0.035 cm3-brainstem are lower in the BO versus VC technique, and with the parameters V50% (whole brain) and V12Gy-cerebrum higher in BO versus VC. Our goal is to keep the dose to the brainstem as low as possible and, if possible, at most between 12 Gy and 15 Gy. The BO technique meets our purposes and is considered clinically acceptable at our institution.

Long-term volumetric analysis of vestibular schwannomas following stereotactic radiotherapy: Practical implications for follow-up

Background and purposeTransient tumor swelling is a well-known phenomenon following radiotherapy for vestibular schwannomas (VS). We analyzed the long-term volumetric changes of VS after LINAC radiosurgery, in order to determine a time interval during which a true tumor progression can be distinguished from a pseudoprogression. MethodsAmong 63 patients with VS treated by one fraction or fractionated radiotherapy, we selected 52 of them who had a minimal follow-up of 5 years. Maximal axial diameter and three-dimensional tumor volume were measured on each MRI scan. Volume changes were interpreted using different error margins ranging from 10 to 20%. Patients were categorized according to the tumor evolution pattern over time. ResultsMedian follow-up was 83 months. One tumor (1.9%) remained stable and 26.9% had continuous shrinkage. Applying an error margin of 13%, a transient tumor enlargement was observed in 63.5% of patients, with a first peak at 6–12 months and a late peak at 3–4 years. A true progression was suspected in 4 (7.7%) patients, tumor regrowth starting after the 3rd or 4th year post-treatment. Only one patient required salvage radiotherapy. ConclusionTransient swelling of VS following radiotherapy is generally an early phenomenon but may occur late. In the first 5 years, a true tumor progression cannot be differentiated from a pseudoprogression. A significant tumor expansion observed on 3 sequential MRI scans after the 3rd year may be suggestive of treatment failure. Long-term follow-up is therefore mandatory and no decision of salvage treatment should be made until the 6th year.

Practical Considerations for Single Isocenter LINAC Radiosurgery of Multiple Brain Metastases

The purpose of this paper is to summarize treatment guidelines for the performance of single isocenter LINAC radiosurgery of multiple brain metastases developed and used by 3 experienced centers. This article is not meant to provide consensus guidelines. Rather, this is a practical, “how we do it” reference without substantial discussion. To serve as a treatment reference, the great majority of the information is presented in topic-specific tables.

The benefits of vestibular schwannoma treatment by the means of gamma knife radiosurgery. Literature review

Domantas Jakštas1, Gabija Pajedienė1, Monika Martusevičienė2 1Lithuanian University of Health Sciences, Medical Academy, Faculty of Medicine 2Lithuanian University of Health Sciences, Kaunas Hospital Abstract Vestibular schwannoma (VS), also known as acoustic neuroma, is a benign, slow-growing tumor that develops due to hyperproduction of Schwan‘s cells surrounding the balance and auditory nerves in the inner ear. Symptoms such as asymmetric hearing loss, tinnitus, dizziness, and imbalance occur as the tumor grows. Significant enlargement of the tumor may exhibit pressure on the surrounding brain structures, leading to various neurological deficits and life-threatening damage to the brain stem. Due to the complex localization of the tumor, surgical treatment is associated with a high risk of complications and more difficult recovery, leading to the increasing use of radiosurgical treatments. Gamma knife stereotaxic radiosurgery is a promising and effective treatment method that is increasingly used to treat VS. Aim: to collect publications on the treatment of vestibular schwannoma with stereotaxic radiosurgery using Gamma knife and to systematically evaluate the benefits provided by this method over traditional microsurgery. Methods. A comprehensive search of English-language literature in the PubMed database was performed. The search was performed using MeSH terms: Gamma knife, radiosurgery, stereotactic radiosurgery, vestibular schwannoma, acoustic neuroma. Article inclusion criteria: Article was published in English Article was not older than 15 years Article was describing the results of vestibular schwannoma treatment by the means of Gamma knife (LINAC radiosurgery and CyberKnife were excluded) Exclusion criteria: Articles, describing the use of other radiosurgery modalities, such as LINAC and CyberKnife Results: with the use of chosen keywords, 60 studies were found. After implementing inclusion and exclusion criteria, 31 articles were selected for further evaluation. After analyzing the information, presented in these articles, we have come to conclusion that Gamma Knife is an effective method of VS treatment, with an advantage as this method can avoid many of the complications associated with open surgical treatment, such as hearing loss, facial or trigeminal nerve dysfunction. Keywords: vestibular schwannoma, gamma knife, stereotactic radiosurgery. https://doi.org/10.53453/ms.2021.06.12

LINAC radiosurgery for glomus jugulare tumors: retrospective - cohort study of 23 patients.

Glomus jugulare tumors (GJTs) are uncommon and locally disruptive tumors that usually arise within the jugular foramen of the temporal bone. Surgery was the treatment of choice up until recently. In the last decades, however, radiosurgery has surfaced as a promising alternative treatment by providing excellent tumor control with low risk of cranial nerve injuries. Our aim was to examine the results of radiosurgery specifically, linear accelerator stereotactic radiosurgery (LINAC SRS) for GJT treatment. We hypothesized that radiosurgery will reduce the size of the tumor and improve neurological symptoms. Between January 1, 1994 and December 31, 2013, 30 patients with GJTs were treated in Sheba Medical Center using LINAC SRS treatment. Comprehensive clinical follow-up was available for 23 patients. Sixteen patients were female and seven males with a median age of 64years, with a range of 18-87years. In 19 of the patients, LINAC SRS was the primary treatment, whereas in the remaining four cases, surgery or embolization preceded radiosurgery. The median treated dose to tumor margin was 14Gy (range 12-27Gy), and the median tumor volume before treatment was 5ml (range 0.5-15ml). Following the LINAC SRS treatment, 14 of 23 patients (60%) showed improvement of previous neurological deficits, nine patients (40%) remained unchanged. At the end of a follow-up, tumor reduction was seen in 13 patients and a stable volume in eight (91% tumor control rate). Two cases of tumor progression were noted. Three patients (13%) had post- SRS complications during the follow-up, two of which achieved tumor control, while in one the tumor advanced. LINAC SRS is a practical treatment option for GJTs, with a high rate of tumor control and satisfactory neurological improvement.

Optimization of MLC parameters for TPS calculation and dosimetric verification: application to single isocenter radiosurgery of multiple brain lesions using VMAT

Linac and MLC-based stereotactic radiosurgery (SRS) using single-isocenter-multiple-target (SIMT) VMAT has become increasingly popular in the management of multi-focal cranial metastases. However, significant geometrical and dosimetric challenges exist due to the typically small target volumes and in most cases, non-isocentric locations. To the best of our knowledge, there hasn’t been a study in the optimization of MLC parameters, in the context of SIMT SRS, to ensure TPS calculation accuracy. In this work, we set out to optimize the dosimetric leaf gap (DLG) for the HD MLC installed on dedicated stereotactic Varian STx systems using a diverse group of 21 clinical SRS and SBRT plans. These plans featured a broad range of target sizes and target-to-isocenter distances that are typical of the stereotactic cases treated on these systems. Dose discrepancies between TPS calculations and verification measurements using a previously validated diode array Delta4 (ScandiDos) were minimized in a balanced manner to accommodate the variety of stereotactic plans. A DLG of 0.6 mm was found to be ‘optimal’ for the HD MLC and for the ‘typical’ plans treated on our STx systems. The finding was independently verified using commercially available 3D polymer gel dosimeter CrystalBallTM (MGS Research Inc.). 3D verification for 6 SIMT SRS plans, consisted of 5 to 15 targets, achieved an average gamma score of 97.3% (σ = 2.0%) on 3%/2 mm criteria with a cutoff isodose level of 20%. We further examined the practice of routine dosimetric verifications including the selection of appropriate detectors and optimal gamma parameters. We found that the commonly used standard 3%/3 mm criteria would have resulted in all but 4 (out of 2840) clinical plans achieving a gamma score of 95% or better, and therefore, losing sensitivity to detect potential dosimetric discrepancies. Based on the characteristics of stereotactic plans, a more stringent distance-to-agreement parameter is needed.

In-Vivo Nerve Tractography for Microstructural Neural Changes after Trigeminal Radiosurgery

Focal radiosurgery is a common treatment option for medically refractory trigeminal neuralgia (TN). Given the paucity of investigational tools to assess the trigeminal nerve changes, assessment of treatment effectiveness is primarily clinical. Diffusion tensor imaging (DTI) provides information on white matter microstructure. We explored the feasibility of trigeminal nerve tractography and assessment of DTI parameters to study microstructural changes after treatment. We hypothesized that trigeminal tractography provides more information than 2D-MR imaging, allowing detection of unique, focal changes in the target area after radiosurgery. 10 medically refractory TN patients (8 males, 2 male, average age 67 years) underwent treatment with Linac radiosurgery using stereotactic cones, 6DOF image guidance & FFF beams, 85 Gy/100% isodose line underwent 3 MR trigeminal nerve tractography before and sequentially at 4mon, 8mo and 12mo after treatment. Multi-tensor tractography was used to extract DTI-derived metrics-axial (AD), radial (RD), mean diffusivity (MD), and fractional anisotropy (FA)-from the trigeminal nerve cisternal segment (Retrogasserian region near pars triangularis through pontine segment of trigeminal nerves) defined as region-of-interest. Areas outside target and the contralateral nerve served as controls. Trigeminal tractography accurately detected the radiosurgical target. At 3months post radiosurgery resulted in 55% drop in FA values at the target with no significant change in FA outside the target, demonstrating highly focal changes after treatment. RD but not AD changed markedly, suggesting that radiosurgery primarily affects myelin. Tractography was more sensitive than conventional gadolinium-enhanced post-treatment MR, since FA changes were detected regardless of trigeminal nerve enhancement. In subjects with long term follow-up, recovery of FA/RD correlated with pain recurrence. DTI parameters accurately detect the effects of focal radiosurgery on the trigeminal nerve, serving as an in vivo imaging tool to study TN.

Correlation of Appearance of MRI Perinidal T2 Hyperintensity Signal and Eventual Nidus Obliteration Following Photon Radiosurgery of Brain AVMs: Combined Results of LINAC and Gamma Knife Centers

A wide variety of radiologic changes occur within and adjacent to the nidus of arteriovenous malformations (AVMs) after stereotactic radiosurgery (SRS). Our objective was to study the magnetic resonance imaging(MRI)-defined changes following photon radiosurgery of AVMs and specifically to correlate the appearance of a perinidal T2 hyperintensity signal with the eventual angiographic obliteration of an AVM nidus in response to SRS treatment. This retrospective study was conducted on 62 patients with brain AVMs who received photon SRS treatments between 2004 and 2017, using either a technique based on a linear accelerator at the Alexandria LINAC Radiosurgery Center in Egypt (21 patients/AVMs) or a technique based on a gamma unit at the Koto Memorial Gamma Knife Center in Japan (41 patients/AVMs). All patients included in the study had serial clinical and radiologic follow-ups for ≥ 2 years after SRS treatments. In the combined study series of 62 patients/AVMs treated with photon SRS, the follow-up MRIs revealed that 50 AVMs (80.6%) showed nonvisualized nidus and 12 AVMs (19.4%) showed decreased nidus size. Radiation-induced changes, defined as appearance of perinidal T2 hyperintensities in post-SRS MRIs, occurred in 34 patients (54.8%). Of the 35 patients with available follow-up angiographic studies, 30 AVMs (85.7%) demonstrated complete nidus obliteration at a mean of 36 months (range: 8-66 months) after SRS. Of the 30 AVMs with both MRI evidence of a nonvisualized nidus and angiographic verification of complete nidus obliteration, 20 AVMs (66.7%) were associated with prior MRI evidence of the appearance of a perinidal T2 hyperintensity signal at an average of 12 months (range: 6-45 months) after SRS. Of the five AVMs with both MRI evidence of decreased nidus size and angiographic verification of partial nidus obliteration, four AVMs (80%) showed perinidal T2 hyperintensity signal on post-SRS follow-up MRIs. Lower Spetzler-Martin grade (p = 0.013), smaller AVM volume (p = 0.017), and appearance of post-SRS perinidal T2 hyperintensity signal (p = 0.007) were the statistically significant independent predictors of AVM obliteration. The appearance of perinidal T2 hyperintensity signal in the post-SRS MRIs had a sensitivity of 66.7%, a specificity of 20%, and an overall accuracy of 60% in predicting the eventual obliteration of the AVM nidus. The present study may help improve our current understanding of the mechanisms behind the radiation-induced tissue changes following AVM SRS. Because the SRS-induced hemodynamic changes within the AVM nidus initiate the cascade of the subsequent formation of perinidal vasogenic brain edema, the appearance of perinidal high T2 signal in the follow-up MRIs after SRS would be a valuable indicator of the AVM response to SRS. The development of perinidal hyperintensity was the strongest predictive factor of AVM obliteration (p = 0.007), with relatively high sensitivity (66.7%) and accuracy (60%) and fairly low specificity (20%), as a prognostic sign of eventual complete angiographic obliteration of the AVM nidus following SRS.

Radiosurgery and fractionated radiotherapy for cavernous sinus meningioma: a systematic review and meta-analysis.

Radiosurgery (RS) and fractionated radiotherapy (FRT) are part of the therapeutic armamentarium for the management of cavernous sinus meningiomas. We propose a systematic review of the local tumor control and clinical outcomes after monofractionated radiosurgical treatment, including gamma knife radiosurgery (GKRS) and linear accelerator (Linac RS), or fractionated radiotherapy. The current review and meta-analysis adhered to the PRISMA guidelines. We performed a search in PubMed, Embase, and Medline based on the following mesh terms, used alone or in diverse combinations, in both title and abstract: "cavernous sinus," "meningioma," "radiosurgery," "gamma knife," "linac," "cyberknife," and "radiotherapy". We screened 425 studies. We selected 36 studies, matching all selection criteria: 24 for GK, 5 for Linac, and 7 for FRT. Were included 2817 patients (GKRS, n = 2047, LinacRS, n = 350, FRT, n = 420). Half of patients benefited from upfront RS or FRT; the other half benefited from adjuvant RS or FRT (combined approach or tumor recurrence). The mean gross target volume (GTV) was smaller for RS as compared to FRT (p = 0.07). The median marginal doses were 13.9Gy (range, 11 to 28) for GKRS and 14Gy (range, 12.8 to 17.7) for LinacRS. For FRT, patients received a mean dose of 51.2Gy (25.5 fractions, 1.85Gy each). The mean overall follow-up values were 48months (range, 15 to 89) for GKRS, 69months (range, 46 to 87) for Linac, and 59.5months (range, 33 to 83) for FRT. PFS at 5years for GKRS, LinacRS, and FRT were respectively 93.6%, 95.6%, and 97.4% (p = 0.32, the Kruskal-Wallis). Monofractionated treatments (GKRS and LinacRS) induced more tumor volume regression than FRT (p = 0.001). Tumor recurrence or progression ranged between 3 and 5.8%, without statistically significant differences between modalities (p > 0.05). Trigeminal symptoms improved in approximately 54%, and III-IV-VI cranial nerves (CN) palsies improved in approximately 45%. After GKRS, visual acuity improved in 21% (not enough data available for other modalities). De novo deficits occurred in 5 to 7.5%. Adverse radiation effects appeared in 4.6 to 9.3% (all techniques pooled). RS achieved a twice-higher rate of tumor volume regression than FRT. GKRS series reported an improvement in visual acuity in 21% of the cases. GKRS, Linac, and FRT provided similar clinical post therapeutic outcomes for the trigeminal and oculomotor CN.

LINAC stereotactic radiosurgery for trigeminal neuralgia \u2013retrospective two-institutional examination of treatment outcomes

BackgroundIn this pooled 2-center series LINAC radiosurgery (SRS) has been applied as a treatment option for a subset of refractory trigeminal neuralgia (TN) patients. This study approached to retrospectively assess the efficacy and safety of LINAC SRS and to provide a brief overview addressed to the technical development from frame-based towards frameless robotic SRS.MethodsFrom 2001 to 2017 n = 55 patients (pts) were treated, n = 28 were female (51%), mean age: 66 years (range 36–93 years); TN etiology: 37 classic TN, 15 multiple sclerosis (MS)-related TN, 2 symptomatic TN, and 1 atypical TN. Previous treatment was present in n = 35 (63.6%) pts. (some multiple or combined) with n = 23 microsurgical vascular decompression and n = 17 percutaneous retrogasserian rhizotomy. A 6 MV LINAC (4–5 mm collimators) was applied in all pts. (n = 26 framebased - n = 29 frameless robotic). The dorsal root entry zone (DREZ) was targeted in n = 35 cases and the retrogasserian target in n = 20 pts. with a homogeneous dose for the entire study cohort (90 Gy). SRS outcome was measured using the Barrow Neurological Institute (BNI) score for pain and hypaesthesia and statistically evaluated by univariate and multivariate analyzes.ResultsMean follow-up (FU) was 30 months (2 lost FU); the total rate of post SRS BNI pain I-IIIa (=painfree w or w/o medication) was 69% (88% for the classic TN pts), 29% (38.8% classic TN) were classified as BNI pain I-II (=painfree w/o medication). A BNI hypaesthesia II-III was present in 9.4% (n = 5) and BNI hypaesthesia IV in n = 2. Between groups analysis demonstrated no correlation of SRS responsiveness with age, gender, MS- or not MS-associated TN, previous surgery, framebased/frameless robotic SRS. DREZ targeting significantly better suppressed TN compared to RG targeting (p = 0.01). Additionally, a statistical trend for a better BNI pain outcome (p = 0.07) along with a significant increase in BNI hypaesthesia (p = 0.01) was found when using a larger partial trigeminal 70 Gy volume.ConclusionOur retrospective analysis support LINAC SRS as an effective and safe treatment option in TN. Frameless robotic SRS of TN is safe when using a dedicated LINAC system. A target definition closer to the brainstem and tendencially a larger target volume were associated with a better outcome for pain.

Validation of MLC-based linac radiosurgery for trigeminal neuralgia.

This study details a validation process for linear accelerator‐based treatment of trigeminal neuralgia using HD‐MLC field collimation. Nine trigeminal neuralgia treatment plans utilizing HD‐MLC were selected for absolute dose measurement at isocenter using a commercial scintillating detector in an anthropomorphic phantom. Four plans were chosen for film dosimetry measurements in each of the three principal planes to assess spatial dose distribution agreement with the treatment planning system. Additionally, trajectory log analysis for each treatment field in the nine cases was performed to assess mechanical positioning accuracy of the MLC system during delivery. Scintillator and film measurements both revealed mean dose agreement at isocenter of better than 3% while FWHM of the 2D dose distribution in each plane showed agreement between plan and measurement within 0.2 mm. Analysis of log files revealed a maximum MLC leaf positioning error of 0.04 mm across 178 treatment fields. In conjunction with a quality‐controlled treatment delivery methodology, an appropriately commissioned treatment planning system can be used for accurate and clinically appropriate design of trigeminal neuralgia treatment plans utilizing HD‐MLC.

SP-0466: Intracranial lesions and dedicated Linac radiosurgery

SP-0466: Intracranial lesions and dedicated Linac radiosurgery

Cavernous sinus meningiomas

Introduction: Tumors of the cranial base arising from or partially involving the cavernous sinus have represented a formidable challenge to neurosurgeons. Stereotactic radiosurgery represents an alternative to microsurgery for the management of cavernous sinus meningiomas. The present study aims to evaluate the results of radiosurgery in a large series of patients treated with a linear accelerator with a long-term follow-up. Patients and Methods: From 1993 through 2007, 462 patients with meningiomas underwent radiosurgery at the Chaim Sheba Medical Center LINAC radiosurgery unit. Of those, 117 had tumors involving predominantly the cavernous sinus. A mean follow-up of 67 months was obtained in 102 patients (range:12 to 180 months). Patients’ age ranged from 31 to 86 years (mean 57). Seventy two (70%) were females. Thirty five patients (34.3%) were initially submitted to microsurgery and 67 (65.6%) underwent stereotactic radiosurgery as the first treatment option. Patients were treated using a linear accelerator with cylindrical collimators in 44 patients (43.1%) and a minimultileaf collimator in 58 patients (56.8%). The prescription dose was delivered to the 60 to 80% isodose line (mean, 68%) in patients treated with cylindrical collimators, and to the 80% in those treated with a single conformal isocenter. Doses ranged between 12 and 17.5 Gy (mean, 13.5 Gy). Median tumor volume was 7.2 cm3 (range 0.61–23 cm3). Results: All patients were available for follow-up at 12 to 180 months after treatment (mean, 68 months; median, 60 months). The actuarial control rate was 98%. Fifty nine patients (58%) had a volume reduction and forty one (40%) had stable tumor volumes at the end of follow-up. Two tumors grew. Overall, 4 patients had a new lasting neurological deficit (facial hypesthesia or pain in two, trochlear neuropathy in two, and visual defect in one), for an incidence of 4% in persistent neurological complications. Conclusions: This series of linear accelerator radiosurgery confirms that in the short and long term, radiosurgery affords excellent control for cavernous sinus meningiomas with a very low incidence of complications. Radiosurgery can thus be regarded as the treatment of choice for cavernous sinus meningiomas.

P14.20 Local control an overall survival after frameless LINAC radiosurgery: a single center experience

Abstract Introduction: Stereotactic radiosurgery (SRS) has been increasingly advocated for 1-3 small brain metastases. Goal of this study was to evaluate the clinical results in patients with brain metastases treated with SRS using a thermoplastic mask non-invasive fixation system and image-guided treatment. MATERIAL AND METHODS: In this single-institution study 48 patients with 77 brain metastases were treated between February 2012 and January 2014. The head fixation was realized using a BrainLAB thermoplastic mask. The prescribed dose was 20 Gy or 18 Gy as a single dose. The SRS were performed with a True Beam STX Novalis Radiosurgery LINAC (Varian Medical Systems). The verification of positioning was done using the BrainLAB ExacTrac ® X-ray 6D system and cone-beam CT. Results: In 69 of 77 (89.6%) treated brain metastases the follow-up was documented on MR imaging performed every 3 months. In 7/69 (10.1%) brain metastases local failure was diagnosed with a mean follow-up time of 10.7 months (range 1-43 months). Estimated 1-year local control was 83.1%. Median progression free survival (PFS) was 3.7 months, largely due to distant brain relapse. A GTV of ≤ 2.0 cm3 was significantly associated with a better PFS than a GTV > 2.0 cm3. We observed 2 cases of radiation necrosis diagnosed by histology after surgical resection. No other cases of severe side effects (CTACE≥3) were observed. CONCLUSION: In our experience local control after frameless (ringless) LINAC based SRS with mean follow-up of 10.7 months is 89.9%. Without the invasive head fixation radiotherapy is more comfortable for the patients.

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.

EP-1560: Is EBT-XD film suitable for linac and Gamma Knife radiosurgery dosimetry verification and audit?

EP-1560: Is EBT-XD film suitable for linac and Gamma Knife radiosurgery dosimetry verification and audit?