Characterization of a Novel 3 Megavolt Linear Accelerator for Dedicated Intracranial Stereotactic Radiosurgery

Abstract

The purpose of this article is to investigate and characterize from a physics perspective the Zap-X (ZAP Surgical Systems, Inc., San Carlos, CA), a new, dedicated self-contained and self-shielded radiosurgery system, focusing on beam energy and performance, leakage, radiation safety, dose delivery accuracy, regulations, quality assurance, and treatment planning. This investigation is required to establish the mechanical and overall performance specifications of the system and to establish baseline parameters for future clinical usage. The applied methods include measurements of energy, focal spot size, beam performance, dosimetry, beam data, treatment planning system, leakage radiation, acceptance testing, and commissioning. The results of the characterization reveal a 3 megavolt (MV) linear accelerator (linac) with a focal spot size of 2 mm, a dose rate of 1,500 MU/min at the isocenter with a dose linearity of 3%, a beam penumbra of less than 3 mm, and beam symmetry of less than 2%. Beam performance, as well as dosimetry characteristics, are suitable for intracranial radiosurgery. It can be concluded that the system was found to meet safety, accuracy, and performance requirements widely accepted in the radiation oncology and radiosurgery industry. Furthermore, the system was shown to meet the practical, clinical needs of the radiosurgery community.

ZAP-X: A Novel Radiosurgical Device for the Treatment of Trigeminal Neuralgia

“…Introduction ZAP-X® (ZAP Surgical Systems, Inc., San Carlos, CA) is a new, image-guided medical linear accelerator (LINAC)-based radiosurgery system dedicated to the treatment of intracranial and cervical spine lesions. ZAP-X is characterized by a 3 megavolt (MV) S-band LINAC with a focal spot size of 2 mm, a dose rate of 1,500 MU/min at the isocenter, with dose linearity of 3%, a beam penumbra of 1.8 mm using the 4-mm collimator, and beam symmetry of less than 2% [1][2]. The ZAP-X linac is mounted within a combination of yoked gimbals, each of which accurately rotates around a common isocenter, thus allowing >2π steradian solid angle beam coverage.…”

“…The ZAP-X linac is mounted within a combination of yoked gimbals, each of which accurately rotates around a common isocenter, thus allowing >2π steradian solid angle beam coverage. ZAP-X is "self-shielded" in that nearly all radiation is contained within the device, allowing it to be used safely without a radiation therapy vault; under standard operating conditions, at 1 m distance from the perimeter of the device, the maximum expected radiation equivalent dose level is below 1 mSv/year, which is equivalent to the limit for public exposure [2].…”

Characterization of the ZAP-X® Peripheral Dose Fall-Off

“…The ZAP-X is shown in Figure 1 and has been described in more detail in previous publications [1][2]. The ZAP-X system has a SAD of 45 cm ( Figure 1).…”

“…The focus of this work is on the direct comparison of detector performance and not on a comprehensive beam performance evaluation which was previously performed [ 2 ]. The smallest 4 mm collimator was chosen for this direct detector comparison since this collimator represents the highest level of characterization difficulty and requires the most precision to accurately determine dose fall-off characteristics.…”

“…This device is intended for stereotactic radiosurgery treatment of benign and malignant intracranial and cervical spine lesions. A 3.0 megavolt (MV) S-band linear accelerator (linac) is the source of therapeutic radiation [ 1 - 2 ]. This radiotherapy system shares with other systems the required accuracy of dose deposition and for rapid peripheral dose fall-off.…”