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BACKGROUND: Repeat Gamma Knife stereotactic radiosurgery (GKSR) procedures are becoming common, especially for brain metastases. It is important to identify tumors requiring treatment at repeat GKSR and it can be challenging to distinguish treated tumors, tumor progression and new tumors. Using the image co-registration tool within the Leksell Gamma Plan software, we developed a technique to aid in the identification of tumors needing treatment. OBJECTIVES: The objective was to explore a new co-registration technique to identify tumors requiring treatment at repeat GKSR procedures. METHODS: Ten patients who underwent repeat GKSR for brain metastases were identified. Contrast-enhanced volumetric T1 magnetic resonance images (MRI) from the previous GKSR were co-registered with the new images and the resulting two-color format image was used to evaluate tumor status. RESULTS: Using the co-registered images, tumors were characterized as: resolved, regressed, stable, larger or new. Overall, 13.6% of tumors completely resolved, 26.2% regressed, 13.1% remained stable, while 7.9% progressed. Thirty-nine percent of tumors were new. CONCLUSIONS: The co-registration technique makes clinically relevant changes conspicuous on MRI. It distinguishes between tumors potentially requiring treatment and those that have been treated successfully. It can be used with tumors other than metastases and for evaluating tumor response at follow-up.
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Neoplasias Encefálicas/cirugía , Neoplasias de la Mama/cirugía , Neoplasias Pulmonares/cirugía , Radiocirugia/instrumentación , Anciano , Neoplasias Encefálicas/secundario , Neoplasias de la Mama/patología , Progresión de la Enfermedad , Femenino , Humanos , Neoplasias Pulmonares/patología , Masculino , Persona de Mediana Edad , Radiocirugia/métodos , Resultado del TratamientoRESUMEN
PURPOSE: The purpose of this study was to evaluate the dosimetric characteristics of each sector of the Leksell Gamma Knife Perfexion (LGK PFX) and to develop tests that can be done for the routine quality assurance checks of the sectors of the LGK PFX. METHODS: The following tests were performed to evaluate the dosimetric characteristics of the sectors: (1) Flash-radiation dose for the 16 mm collimator, (2) transit-radiation dose for the 8 and 4 mm collimators, (3) sector leakage within the radiation cavity and, (4) sector output uniformity. In these tests, the Elekta ABS phantom was used. A micropoint ion-chamber Exradin A16 was placed at the center of the phantom for all measurements. RESULTS: With the version 8.0 of the control software of the MCU in the LGK PFX, the average flash-radiation dose per sector for the 16 mm collimator was measured to be 0.423 ± 0.003 cGy, and the average transit-radiation dose per sector for the 8 and 4 mm collimators was measured to be 0.169 ± 0.0009 and 0.147 ± 0.020 cGy, respectively. The calibration dose rate on the day of measurements was 280.8 cGy/min. Here, the authors have introduced a new concept of "equivalent-time-duration" (ETD) to represent the time duration, during which the flash-radiation or the transit-radiation dose is delivered. The ETD is a quotient of the measured dose of the flash-radiation or the transit-radiation and the respective calibrated dose rate for the 16, 8, or 4 mm collimator. The ETD constancy is an indicator of the constancy of the sector movements. The average value of ETD per sector was measured to be 724 ± 6, 313 ± 2, and 311 ± 45 ms for the 16, 8, and 4 mm collimators, respectively. During monthly spot checks, the authors have been measuring the total ETD for the flash-radiation when all eight sectors are open with the 16 mm collimator. The average value of the total ETD of the last 40 consecutive months was measured to be 642 ± 10 ms. This number is a useful quality parameter for the LGK PFX, which can be used to establish the base-line performance of the collimators of the LGK PFX. The reader is alerted that with the newly introduced version 9.0 of the control software of the MCU in the LGK PFX, the flash-radiation and the transit-radiation doses have become practically zero due to the fact that the treatment time is now corrected to compensate for these radiation doses. The sector output uniformity for the 16, 8, and 4 mm collimators was determined to be 98.9%, 97.3%, and 96.6%, respectively. The total leakage radiation with in the radiation cavity from all sectors was measured to be 0.17% of the dose output for the 16 mm collimator. CONCLUSIONS: Our measurements show that the dosimetric characteristics of all sectors of the LGK PFX are satisfactory. The authors recommend that the sector performance of the LGK PFX be determined initially at the time of installation of the LGK PFX and thereafter, at least annually. Similarly, our recommendation is that the total flash-radiation dose for the 16 mm collimator and the corresponding ETD value be measured on a monthly basis. Should any change in the sector movement occur, it will be revealed by the sector performance and the measurement of ETD.
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Análisis de Falla de Equipo/instrumentación , Análisis de Falla de Equipo/normas , Garantía de la Calidad de Atención de Salud , Radiometría/normas , Radiocirugia/instrumentación , Radiocirugia/normas , Control de Calidad , Dosificación Radioterapéutica , Estados UnidosRESUMEN
OBJECT: Stereotactic radiosurgery (SRS) is an important management option for patients with small- and medium-sized vestibular schwannomas. To assess the potential role of SRS in larger tumors, the authors reviewed their recent experience. METHODS: Between 1994 and 2008, 65 patients with vestibular schwannomas between 3 and 4 cm in one extracanalicular maximum diameter (median tumor volume 9 ml) underwent Gamma Knife surgery. Seventeen patients (26%) had previously undergone resection. RESULTS: The median follow-up duration was 36 months (range 1-146 months). At the first planned imaging follow-up at 6 months, 5 tumors (8%) were slightly expanded, 53 (82%) were stable in size, and 7 (11%) were smaller. Two patients (3%) underwent resection within 6 months due to progressive symptoms. Two years later, with 63 tumors overall after the 2 post-SRS resections, 16 tumors (25%) had a volume reduction of more than 50%, 22 (35%) tumors had a volume reduction of 10-50%, 18 (29%) were stable in volume (volume change < 10%), and 7 (11%) had larger volumes (5 of the 7 patients underwent resection and 1 of the 7 underwent repeat SRS). Eighteen (82%) of 22 patients with serviceable hearing before SRS still had serviceable hearing after SRS more than 2 years later. Three patients (5%) developed symptomatic hydrocephalus and underwent placement of a ventriculoperitoneal shunt. In 4 patients (6%) trigeminal sensory dysfunction developed, and in 1 patient (2%) mild facial weakness (House-Brackmann Grade II) developed after SRS. In univariate analysis, patients who had a previous resection (p = 0.010), those with a tumor volume exceeding 10 ml (p = 0.05), and those with Koos Grade 4 tumors (p = 0.02) had less likelihood of tumor control after SRS. CONCLUSIONS: Although microsurgical resection remains the primary management choice in patients with low comorbidities, most vestibular schwannomas with a maximum diameter less than 4 cm and without significant mass effect can be managed satisfactorily with Gamma Knife radiosurgery.
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Neoplasias de los Nervios Craneales/cirugía , Neuroma Acústico/cirugía , Radiocirugia , Enfermedades Vestibulares/cirugía , Adulto , Anciano , Anciano de 80 o más Años , Neoplasias de los Nervios Craneales/patología , Relación Dosis-Respuesta en la Radiación , Enfermedades del Nervio Facial/epidemiología , Enfermedades del Nervio Facial/etiología , Femenino , Estudios de Seguimiento , Trastornos de la Audición/epidemiología , Trastornos de la Audición/etiología , Humanos , Estimación de Kaplan-Meier , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Neuroma Acústico/patología , Complicaciones Posoperatorias/epidemiología , Radiocirugia/efectos adversos , Estudios Retrospectivos , Gestión de Riesgos , Análisis de Supervivencia , Resultado del Tratamiento , Enfermedades Vestibulares/patología , Adulto JovenRESUMEN
PURPOSE: Traditionally, the dose-rate calibration (output) of the Leksell Gamma Knife (LGK) unit is performed using a 160 mm diameter plastic spherical phantom provided by the vendor of the LGK, Elekta Instrument AB. The purpose of this study was to evaluate variations in the Elekta spherical phantom and to assess its impact and use for the LGK calibration. METHODS: Altogether, 13 phantoms from six different centers were acquired, 10 of these phantoms were manufactured within the past 10 years and the last 3 approximately 15-20 years ago. To assess variation in phantoms, the diameter and mass densities were measured. To assess the impact on LGK calibration, the output of two models of LGK (LGK Perfexion and LGK 4C) were measured under identical irradiation conditions using all 13 phantoms for each LGK model. RESULTS: The mean measured deviation in diameter from expected nominal 160 mm for 13 phantoms was 0.51 mm (range of 0.09-1.51 mm). The mean measured phantom mass density for 13 phantoms was 1.066 +/- 0.019 g/cm3 (range of 1.046-1.102 g/cm3). The percentage deviation of output for individual phantom from mean of 13 phantom outputs ranged from -0.37% to 0.55% for LGK Perfexion. Similarly, the percentage deviation of output for individual phantom from mean of 13 phantom outputs ranged from -0.72% to 0.47% for LGK 4C. CONCLUSIONS: This study demonstrated that small variations in terms of phantom size and mass density of the phantom material do not have a significant impact on dose-rate measurements of the Leksell Gamma Knife. Also, date of manufacture of the phantom did not show up to be a significant factor in this study.
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Fantasmas de Imagen , Plásticos , Radiocirugia/instrumentación , Resinas Acrílicas , Butadienos , Calibración , Poliestirenos , Dosis de RadiaciónRESUMEN
Three types of films, Kodak EDR2, Gafchromic EBT, and Gafchromic MD-V2-55, were used to measure relative output factors of 4 and 8 mm collimators of the Leksell Gamma Knife Perfexion. The optical density to dose calibration curve for each of the film types was obtained by exposing the films to a range of known doses. Ten data points were acquired for each of the calibration curves in the dose ranges from 0 to 4 Gy, 0 to 8 Gy, and 0 to 80 Gy for Kodak EDR2, Gafchromic EBT, and Gafchromic MD-V2-55 films, respectively. For the measurement of relative output factors, five films of each film type were exposed to a known dose. All films were scanned using EPSON EXPRESSION 10000 XL scanner with 200 dpi resolution in 16 bit gray scale for EDR2 film and 48 bit color scale for Gafchromic films. The scanned images were imported in the red channel for both Gafchromic films. The background corrections from an unexposed film were applied to all films. The output factors obtained from film measurements were in a close agreement both with the Monte Carlo calculated values of 0.924 and 0.805 for 8 and 4 mm collimators, respectively. These values are provided by the vendor and used as default values in the vendor's treatment planning system. The largest differences were noted for the Kodak EDR 2 films (-2.1% and -4.5% for 8 and 4 mm collimators, respectively). The best agreement observed was for EBT Gafchromic film (-0.8% and +0.6% differences for 8 and 4 mm collimators, respectively). Based on the present values, no changes in the default relative output factor values were made in the treatment planning system.
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Dosimetría por Película/instrumentación , Dosimetría por Película/métodos , Radiocirugia/instrumentación , Diseño Asistido por Computadora , Transferencia de Energía , Diseño de Equipo , Análisis de Falla de Equipo , Dosificación Radioterapéutica , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
The calibration of Leksell Gamma Knife Perfexion (LGK PFX) is performed using a spherical polystyrene phantom 160 mm in diameter, which is provided by the manufacturer. This is the same phantom that has been used with LGK models U, B, C, and 4C. The polystyrene phantom is held in irradiation position by an aluminum adaptor, which has stainless steel side-fixation screws. The phantom adaptor partially attenuates the beams from sectors 3 and 7 by 3.2% and 4.6%, respectively. This unintended attenuation introduces a systematic error in dose calibration. The overall effect of phantom-adaptor attenuation on output calibration of the LGK PFX unit is to underestimate output by about 1.0%.
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Neoplasias/cirugía , Radiocirugia/instrumentación , Radiocirugia/métodos , Aluminio/química , Calibración , Humanos , Modelos Estadísticos , Fantasmas de Imagen , Poliestirenos/química , Radiometría/métodos , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por Computador/instrumentación , Acero Inoxidable , Factores de TiempoRESUMEN
A new model of Leksell Gamma Knife(R) (LGK), known as Perfexion (LGK PFX), was introduced by Elekta Instrument, AB, Sweden, in 2006. This model has a radically different design from the earlier models U, B, C and 4C. Dosimetric characteristics of LGK PFX, technical differences between LGK PFX and LGK 4C, experience gained with acceptance testing and commissioning of the LGK PFX, and comparison between LGK PFX and LGK 4C are presented in this study. Excellent agreement is found between the manufacturers recommended values of absorbed dose rate, relative output factors for 4 and 8 mm collimators, coincidence of mechanical and dosimetric isocenter, FWHM for beam profiles for various collimators and those reported in the present study. Excellent agreement is also found between the dosimetric characteristics of LGK PFX and LGK 4C for the 4 and 8 mm collimators. Examples of clinical cases treated with LGK PFX and impact of LGK PFX on workflow and dosimetric conformity of treatment planning is also given. The set up and treatment of patients on the LGK PFX is much more efficient since it is a fully automated system. The system also provides more options to generate plan with high dosimetric conformity.
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OBJECT: The recently introduced Leksell Gamma Knife (LGK) Perfexion is an entirely new system with a different beam geometry compared with the LGK 4C. The new Perfexion system has 192 cobalt-60 sources that are fixed on 8 sectors (each sector has 24 sources). Each sector can be moved independently of the others and can be set to 1 of 5 different positions: 3 positions defining collimator sizes of 4, 8, and 16 mm; an off position (sources are blocked); and a home position. The purpose of this study is to compare the dosimetric characteristics of the GK 4C and the Perfexion models. This comparison is important especially for the treatment of functional disorders when only a single shot with the 4- or 8-mm collimator is used. METHODS: A 160-mm-diameter spherical polystyrene phantom was used for all measurements and calculations. The irradiation geometry consisted of the placement of a single shot at the center of this phantom. Comparisons were made among different dosimetric parameters obtained from calculations performed using Leksell GammaPlan v. 8.0 and measurements performed using film dosimetry. The dosimetric parameters investigated were dose profiles for all collimators in all 3 stereotactic planes (x, y, and z) including the full width at half maximum and the penumbra for each profile, cumulative dose-volume histograms, the volume encompassed by the 50% isodose surface, the mean doses delivered to a defined matrix volume, and relative output factors for all collimator sizes. RESULTS: There was excellent agreement between the dosimetric parameters of GK 4C and Perfexion for the 4- and 8-mm collimators. CONCLUSIONS: The results of this study suggest that consistent treatments of functional disorders will be delivered using either GK 4C or Perfexion.