Leksell Gamma Knife Perfexion Research Articles

Dosimetric comparison of the Leksell Gamma Knife Perfexion and 4C

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. 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. There was excellent agreement between the dosimetric parameters of GK 4C and Perfexion for the 4- and 8-mm collimators. The results of this study suggest that consistent treatments of functional disorders will be delivered using either GK 4C or Perfexion.

SU‐GG‐T‐445: Dosimetric Analysis of Attenuation in the Leksell Gamma Knife PERFEXION Calibration Phantom Adaptor

Purpose: The purpose of this study was to evaluate the attenuation of 16 mm beams caused by the ELEKTA calibration phantom adaptor used for the new Leksell Gamma knife PERFEXION (PFX). Method and Materials: For the calibration of PFX, Elekta AB provides a 160 mm diameter polystyrene phantom with an aluminum adaptor of C‐shape which has stainless steel fixation screws for holding the phantom in the irradiation position in PFX. An Exradin A16 ion chamber (collecting volume 0.007 cm3) and a Standard Imaging MAX 4000 electrometer were used to measure radiation output at the center of the 160 mm diameter polystyrene phantom for each of eight identical sectors and 16 mm collimator. Results: While studying the uniformity of output from each of the 8 sectors it was noticed that for sector No. 3 (270 degree) and sector No. 7 (90 degree), the outputs measured were lower by about 2% as compared to other sectors. On detailed investigation with Kodak EDR2 film, we found that for these two sectors, there were 2 beams of 16 mm diameter passing through the aluminum adaptor and the stainless steel fixation screws which caused attenuation of these two beams and hence a reduction in output. Conclusion: The attenuation by phantom adaptor introduces a systematic error in output calibration of PFX. The overall reduction in output measured for all 8 sectors combined is about 0.5%. We suggest that until Elekta AB redesigns a new phantom adaptor for PFX calibration, physicists should be aware of the attenuation of 16 mm beams by the adaptor and incorporate this effect in the output calibration of the PERFEXION.

SU‐GG‐T‐450: Measurement of Relative Output Factors for the Leksell Gamma Knife PERFEXION by Film Dosimetry

Purpose: To measure relative output factors (ROFs) for 4 and 8 mm collimators for the Leksell Gamma Knife PERFEXION unit. Effective ROFs calculated by Monte Carlo (MC) by ELEKTA and used in the Gamma Plan 8.0 treatment planning system are 0.805, 0.924 for 4 and 8 mm collimators, respectively. Method and Materials: Three types of films, Kodak EDR2, gafchromic EBT and MD‐V2‐55, were used within the spherical polystyrene phantom of diameter of 160 mm. To obtain calibration curve 10 films were exposed to doses of 0–400, 0–800, 0–8000 cGy for EDR2, EBT, MD‐V2‐55 films, respectively. Three samples of each film type were then exposed in identical setup for 4, 8 and 16 mm collimators. Films were scanned by EPSON EXPRESSION 10000 XL scanner with 200 dpi resolution in 16‐bit grayscale for radiographic and 48‐bit color for gafchromic film and imported in red channel. Films were evaluated by FilmQA version 2.0.1215 software. Fifth degree polynomial fit for calibration curve was used and background corrections applied for all films. Doses delivered to the center of each of studied films by 4, 8, 16 mm collimators were obtained and ROFs calculated and corrected for transit dose. Results: Measured ROFs and deviations compared to MC calculated value for 8 mm collimator were 0.899 (−2.7%), 0.917 (−0.8%), and 0.920 (−0.4%) for EDR2, EBT, and MD‐V2‐55 films, respectively. Measured ROFs and deviations compared to MC calculated value for 4 mm collimator were 0.778 (−3.4%), 0.818 (1.6%), and 0.804 (−0.1%) for EDR2, EBT, and MD‐V2‐55 films, respectively. Conclusion: MD‐V2‐55 film seems to be an ideal dosimeter for small stereotactic field ROFs measurements. All results obtained in this study were in close agreement with MC values. Largest deviations noted from the MC were for EDR 2 films. The closest agreement with MC values was observed for MD‐V2‐55 films.

THE LEKSELL GAMMA KNIFE PERFEXION AND COMPARISONS WITH ITS PREDECESSORS

The objective of this study is to introduce a new radiosurgical device, the Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden). Design and performance characteristics are compared with previous models of the gamma knife in a clinical setting. Performance-related features in the design of the new radiosurgical system are described, and the ability to create complex shapes of isodose volumes even with a single isocenter is demonstrated. The concept of "dynamic shaping" of dose distribution is introduced as a means of decreasing the exposure to structures outside the target. Dose plans for the Leksell Gamma Knife Models B, 4C, and Perfexion have been created for target pathologies to illustrate how the software and hardware of the new radiosurgical system can increase treatment quality, decrease treatment time, and increase patient comfort. Radiation doses to critical organs in the rest of the human body are compared. The automated collimator arrangement in the Perfexion makes it possible to produce more complex treatment volumes than with previous models of the gamma knife. This results from the enhanced ability to shape isodose volumes, even for single isocenters. The collimator arrangement and the patient positioning system also allow shorter patient transit times, reducing unwanted radiation exposure during movement between isocenters. The Perfexion exceeds the capabilities of previous gamma knife models in terms of treatment efficiency, conformity, and radiation protection. These qualities enable treatment of larger target volumes, especially close to eloquent areas. Pathologies previously inaccessible in the head and neck are now treatable due to the increased volume of the radiation cavity.

THE LEKSELL GAMMA KNIFE PERFEXION AND COMPARISONS WITH ITS PREDECESSORS

The objective of this study is to introduce a new radiosurgical device, the Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden). Design and performance characteristics are compared with previous models of the gamma knife in a clinical setting. Performance-related features in the design of the new radiosurgical system are described, and the ability to create complex shapes of isodose volumes even with a single isocenter is demonstrated. The concept of "dynamic shaping" of dose distribution is introduced as a means of decreasing the exposure to structures outside the target. Dose plans for the Leksell Gamma Knife Models B, 4C, and Perfexion have been created for target pathologies to illustrate how the software and hardware of the new radiosurgical system can increase treatment quality, decrease treatment time, and increase patient comfort. Radiation doses to critical organs in the rest of the human body are compared. The automated collimator arrangement in the Perfexion makes it possible to produce more complex treatment volumes than with previous models of the gamma knife. This results from the enhanced ability to shape isodose volumes, even for single isocenters. The collimator arrangement and the patient positioning system also allow shorter patient transit times, reducing unwanted radiation exposure during movement between isocenters. The Perfexion exceeds the capabilities of previous gamma knife models in terms of treatment efficiency, conformity, and radiation protection. These qualities enable treatment of larger target volumes, especially close to eloquent areas. Pathologies previously inaccessible in the head and neck are now treatable due to the increased volume of the radiation cavity.