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Background: Treatment of patients with multiple brain metastases has shifted to stereotactic radiosurgery, withholding whole-brain (WB) radiation therapy. However, radiation toxicity to the brain is a concern when treating multiple brain lesions with single-fraction stereotactic radiosurgery., Objective: The purpose of this study was to determine the changes in brain radiation doses when treating various numbers of targets and lesion volumes., Methods: We simulated different treatment plans with different combinations of varying tumor volumes including 0.1, 0.5, 1, 2, and 5 cm3, and tumor numbers including 1, 3, 5, 10, 15, 20, and 25. Treatment planning was performed for all combinations in a computerized tomography of the head of a patient, using Leksell GammaPlan version 10.1.1 (Elekta AB, Stockholm, Sweden). Two different dosing strategies were used. In the lower-prescription dosing schedule, a marginal dose was given to the 50% isodose line, and 20 Gy were used when the number of lesions was less than 15 and 18 Gy were applied when the number of lesions was equal to or more than 15. In the higher-prescription dosing schedule, a marginal dose of 24 Gy was used for lesions of less than 5 cm3 and 20 Gy were applied for lesions equal to 5cm3. The mean WB dose, the WB integral dose, and the volume of brain receiving 12 Gy (V12 Gy) were calculated for each scenario. Also, the beam-on time of the Gamma Knife 4C unit was reported for all treatment scenarios., Results: Regression analysis showed that the total tumor volume was a more significant predictor of V12 Gy than the number of lesions, and a linear correlation between the total tumor volume and V12 Gy was found. We also found that the total tumor volume was a more significant predictor of the mean WB dose and the WB integral dose compared to the number of lesions., Conclusion: Our results suggest that multiple small to mid-sized lesions could be safely treated with a single-fraction gamma knife., (© 2017 S. Karger AG, Basel.)

Background: Target identification is important for radiosurgery for arteriovenous malformations (AVMs). Targets defined by different imaging modalities may be inconsistent in practice., Objectives: The goal of this study is to review and analyze the consistency between targets defined by different imaging modalities in radiosurgery for AVMs., Methods: From March 2007 to June 2011, AVM patients for radiosurgery whose targets were delineated by angiography/computed tomography (CT)/magnetic resonance imaging (MRI) were reviewed. Spetzler-Martin grades, hemorrhage history, and treatment volumes were checked. Dice similarity coefficients (DSCs) between targets were calculated and analyzed., Results: Twenty-three patients were enrolled. The mean DSCs were between 0.37 and 0.51 for targets by different modalities. There was no significant difference in DSCs regarding Spetzler-Martin grades and hemorrhage history. For CT-delineated target volumes <3 cm3, MRI-delineated target volumes <5 cm3, and angiography-delineated target volumes <2 cm3, the DSCs between the different image modalities were significantly decreased., Conclusions: Consistency between targets delineated using different image modalities was likely to be unsatisfactory and worsen significantly in niduses with volumes <5 cm3. An iterative multimodality approach to confirm the delineated targets of AVMs is suggested to be indispensable for robust treatment in radiosurgery., (© 2017 S. Karger AG, Basel.)

Purpose/objectives: The purpose of this study was to evaluate the effect of the number of brain lesions for which stereotactic radiosurgery (SRS) was performed on the dose volume relationships in normal brain., Materials and Methods: Brain tissue was segmented using the patient's pre-SRS MRI. For each plan, the following data points were recorded: total brain volume, number of lesions treated, volume of brain receiving 8 Gy (V8), V10, V12, and V15., Results: A total of 225 Gamma Knife® treatments were included in this retrospective analysis. The number of lesions treated ranged from 1 to 29. The isodose for prescription ranged from 40 to 95% (mean 55%). The mean prescription dose to tumor edge was 18 Gy. The mean coverage, selectivity, conformity, and gradient index were 97.5%, 0.63, 0.56, and 3.5, respectively. The mean V12 was 9.5 cm3 (ranging from 0.5 to 59.29). There was no correlation between the number of lesions and brain V8, V12, V10, or V15. There was a direct and statistically significant relationship between the brain volume treated (V8, V10, V12, and V15) and total volume of tumors treated (p < 0.001). In our study, the integral dose to the brain exceeded 3 J when the total tumor volume exceeded 25 cm3., Conclusions: The number of metastatic brain lesions treated bears no significant relationship to total brain tissue volume treated when using SRS. The fact that the integral dose to the brain exceeded 3 J when the total tumor volume exceeded 25 cm3 is useful for establishing guidelines. Although standard practice has favored using whole brain radiation therapy in patients with more than 4 lesions, a significant amount of normal brain tissue may be spared by treating these patients with SRS. SRS should be carefully considered in patients with multiple brain lesions, with the emphasis on total brain volume involved rather than the number of lesions to be treated., (© 2017 S. Karger AG, Basel.)

Background: All physicians seek to improve the patient experience. In an awake surgical procedure, the patient has a unique opportunity to comment on all aspects of care. The provision of a positive experience is part of quality health care. Our purpose was to define this experience to determine areas for improvement., Methods: We evaluated 125 patients who underwent stereotactic radiosurgery using a frame-based, gamma knife technique. Patients were surveyed by a nurse practitioner across all elements of their procedural experience prior to same-day discharge., Results: The radiosurgery was completed in all patients with same-day discharge. In an initial 100-patient cohort, 89 patients said they had received adequate oral and/or intravenous sedation before the procedure. All 100 patients said that they felt comfortable before stereotactic frame application, and all patients later remembered frame application. These patients described frame application as very or adequately comfortable (n = 73), minimally uncomfortable (n = 18), or very uncomfortable (n = 9). Neuroimaging was described as very or adequately comfortable (n = 93), minimally uncomfortable (n = 3), or very uncomfortable (n = 4). Radiosurgery in the gamma knife unit was found to be very or adequately comfortable (n = 99) or very uncomfortable (n = 1). We evaluated how 8 separate factors may have contributed to survey responses related to procedural comfort. These factors included intravenous line placement, delivery of sedation medications, application of the head frame, having the MRI, having radiosurgery on the gamma knife bed, removal of the stereotactic frame, communication with caregivers, and knowing what to expect beforehand. We asked the patients to rate their nursing care during the radiosurgery experience, and 'excellent' was chosen by all initial 100 patients. Other elements of the procedure were also studied as well as suggestions for improvement. As a secondary objective, we then modified our protocol to include sodium bicarbonate added to the local anesthetic for frame application and evaluated an additional cohort of 25 patients., Conclusions: Utilizing a system of physician and nursing education, together with pharmacological sedation and efficient procedural steps, patients said that intravenous line placement (91%), stereotactic frame application (74%), MRI (93%), receiving radiosurgery in the unit (99%), frame removal (84%), communication with caregivers (100%), and knowing what to expect beforehand (97%) were either very or adequately comfortable. Specific evaluations of care processes can lead to care improvement., (© 2016 S. Karger AG, Basel.)

Aims: We analyzed the efficiency of the Leksell Gamma Knife Perfexion (LGK PFX) in the treatment of multiple metastases and benign tumors. We also compared treatment planning conformity between LGK PFX and LGK 4C for benign tumors., Method: Over a 6-week interval, 37 patients (21 with multiple brain metastases and 16 with benign tumors) underwent radiosurgery using LGK PFX at the University of Pittsburgh. We created dose plans for all patients using Leksell Gamma Plan for LGK PFX and LGK 4C. The same doses were prescribed for both LGK PFX and LGK 4C., Results: No significant difference was observed between LGK 4C and LGK PFX for total beam-on time. The median reduction in setup time on the LGK PFX was 53 min per patient (range 19-125 min) for multiple metastases. The median reduction in setup time on the LGK PFX for benign tumors was 16 min per patient (range 5-53 min). There was no significant difference in the dose conformality between LGK 4C and LGK PFX., Conclusions: This study demonstrated that in addition to its enhanced cranial reach, LGK PFX provided a significant improvement in efficiency for patients with multiple brain metastases. For benign tumor radiosurgery LGK PFX provided improvement in efficiency without a significant difference in conformality., (2009 S. Karger AG, Basel.)

Computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) provide complementary information for treatment planning in stereotactic radiosurgery. We evaluated the localization accuracy of MRI and PET compared with CT. Two kinds of phantoms applicable to the Leksell G stereotactic skull frame (Elekta, Tokyo) were developed. Deviations of measured coordinates at target points (x = 50, 100, 150; y = 50, 100, 150) were determined on different axial planes (z = 30-140 for MRI and CT study and Z = 50-120 for PET and CT study). For MRI, the deviations were no more than 0.8 mm in each direction. For PET, the deviations were no more than 2.7 mm. For both imaging modalities studied, accuracy was at or below the imaging resolution (pixel size) and should be considered useful for clinical stereotactic planning purposes., (Copyright 2006 S. Karger AG, Basel.)

The radiosurgical planning of meningiomas frequently necessitates compromises between irradiating tumour and risking damage to adjacent structures. In selected cases, we resolved this by excluding part of the tumour from the prescription isodose volume. Most of these compromises or 'suboptimal' plans achieved growth control. Growth control could not be related to conformity indices or to various measures of the radiation dose received by the meningioma. Examining recurrences, 75% arose from dura outside the original treatment field. These findings are discussed in terms of dose prescription protocols and the use of conformity indices in planning. The importance of the dural origin of meningiomas is well established in surgical practice, as reflected by Simpson's grades, but may be equally significant in radiosurgical practice., (2004 S. Karger AG, Basel.)

The new DIN ('Deutsche Industrie-Norm') 6875-1, which is currently being finalised, deals with quality assurance (QA) criteria and tests methods for linear accelerator and Gamma Knife stereotactic radiosurgery/radiotherapy including treatment planning, stereotactic frame and stereotactic imaging and a system test to check the whole chain of uncertainties. Our existing QA program, based on dedicated phantoms and test procedures, has been refined to fulfill the demands of this new DIN. The radiological and mechanical isocentre corresponded within 0.2 mm and the measured 50% isodose lines were in agreement with the calculated ones within less than 0.5 mm. The measured absorbed dose was within 3%. The resultant output factors measured for the 14-, 8- and 4-mm collimator helmet were 0.9870 +/- 0.0086, 0.9578 +/- 0.0057 and 0.8741 +/- 0.0202, respectively. For 170 consecutive tests, the mean geometrical accuracy was 0.48 +/- 0.23 mm. Besides QA phantoms and analysis software developed in-house, the use of commercially available tools facilitated the QA according to the DIN 6875-1 with which our results complied.

Stereotactic radiosurgery has become a more widely employed modality of treatment for acoustic neuromas, but controversy still arises regarding the safety and efficacy of the technique. In general, radiation doses have been reduced over time. Since beginning treatments of acoustic neuromas with the Gamma Knife at the University of Miami/Jackson Memorial Medical Center in 1994, a dose regimen was adopted by the first author employing limited doses selected on the basis of tumor size with the anterior and medial regions of the prescription isodose surface kept just inside the gadolinium-enhanced limit of the tumor, in order to protect the facial nerve and brainstem. The records of patients treated for unilateral tumors were retrospectively reviewed. Fifty-two patients, aged 23-83 years, were treated with peripheral tumor doses of 10-14 Gy at the 45-70% isodoses. No patient developed new facial weakness or sensory loss; 3 patients had minor transient facial twitching within a few months of treatment. Of 34 patients followed more than 1 year (range 14-100 months, mean 43.4 months, median 37 months), 17 tumors reduced in size, 16 remained unchanged, and 1 increased in size. One patient, who had radiosurgery as planned postoperative adjuvant treatment after partial resection of a large tumor, developed an enlarging peritumoral arachnoid cyst that required surgical resection 79 months after radiosurgery. Patients with good pretreatment hearing retained approximately the same subjective level of hearing. Very good control of unilateral acoustic neuroma has been achieved by a limited-dose scheme that produces minimal complications, but due to the frequently indolent course of these tumors, continued long-term monitoring will be necessary., (2004 S. Karger AG, Basel.)

Objective: To evaluate geometric and dosimetric inaccuracies in the irradiation of the rat brain with the Leksell Gamma Knife., Materials and Methods: Altogether three types of dosimeters were employed for these measurements: (a) a thermoluminescent dosimeter, (b) a semiconductor detector and (c) a polymer gel dosimeter. The thermoluminescent dosimeter and the semiconductor detector were calibrated using an ion chamber and then implanted in the brain of a rat cadaver and used for absolute dose determination. A special glass phantom mimicking exactly the shape of the rat body filled with the polymer gel was used for measurements of the relative dose distribution and evaluation of geometric inaccuracies during the stereotactic irradiation in the rat brain., Results: Both thermoluminescent and semiconductor detectors, due to their size, measured mean doses. The observed results demonstrated that the Leksell GammaPlan can be employed for the calculation of absorbed doses in irradiation of experimental animals. In our case, it was necessary to apply a correction factor of 1.078 for the absolute absorbed dose to obtain reliable results. A comparison of calculated dose profiles using the treatment planning system in all three axes with those measured by the polymer gel dosimeter demonstrated a very good geometric agreement with the mean deviation in profile position of 0.5 mm., Conclusion: The results indicate that this technique can effectively check the geometric and dosimetric accuracy of stereotactic irradiation in the rat brain. The Leksell GammaPlan can be employed for the calculation of absorbed doses, but the correction factor of 1.078 had to be applied for the absolute dose calculations in our irradiation geometry., (Copyright 2002 S. Karger AG, Basel)

Accuracy of pallidotomy lesion placement was assessed by comparing actual lesion locations with expected pallidotomy lesion locations based on stereotaxy. Actual and expected lesions were compared in anteroposterior, dorsoventral and lateral axes. In 22 pallidotomies, actual lesion locations were determined using axial MR images. Expected lesion locations were calculated using a starting point derived from preoperative computerized tomography, displacements from the starting point based on microelectrode-driven electrophysiological refinement, and the trajectory angle of the lesioning tract relative to the anterior-posterior commissural plane. On average, actual lesion locations were found 2.91 +/- 2.23 mm posterior, 3.22 +/- 2.49 mm ventral, and 0.05 +/- 1.80 mm lateral compared to the expected lesion location. Discrepancies between the actual lesion and expected lesion locations may be mostly accounted for by posterior and ventral lesion spread from the exposed electrode tip, in-plane and volume averaging effects associated with MR images, and possible brain shifting during surgery. However, despite the remaining small differences between actual and expected lesion location, good clinical outcome of reduced dyskinesias and 'off' time along with UPDRS-based improvement in mentation, motor and activity of daily living measures was observed.

Artifacts in magnetic resonance imaging (MRI) may lead to anatomical distortion and inaccurate stereotactic coordinates. A special phantom for MRI and computed tomography (CT) was built to test the quality and precision of the two neuroradiological procedures. The phantom is fixed with the Leksell frame, and it has 15 orthogonal markers visible by CT and MRI techniques. The coordinates of the markers were calculated first on the CT scans and then on MR images. Two groups of different distortions were analysed: artifacts depending on the frame and its components and artifacts depending on the MR unit and image characteristics. A good target-coordinate correlation was found between CT and MRI in the axial plane, while in the coronal plane there was always a small error. This error is not constant, but changes from test to test, consequently it is hard to reform the image.

A Leksell Gamma Unit was commissioned and a Lars Leksell Center for Radiosurgery was established at the University of Virginia Health Sciences Center in March 1989. At that time a formal quality assurance program designed for the Leksell Gamma Unit was put into effect. This paper will review the components of suggested daily, monthly, semiannual and annual quality assurance reviews of United States Nuclear Regulatory Commission regulatory as well as nonregulatory items for Leksell Gamma Units. The acceptance criterion for each quality assurance test has been established based on federal requirements and the recommendations of national scientific organizations as well as the practical experience gained from this quality assurance program.