The accurate measurement of the linear accelerator (linac) radiation isocenter is critical, especially for stereotactic treatment. Traditional quality assurance (QA) procedure focuses on the measurement of single radiation isocenter, usually of 6 megavoltage (MV) photon beams. Single radiation isocenter is also commonly assumed in treatment planning systems (TPS). Due to different flattening fi...

Single-isocenter volumetric modulated arc therapy (VMAT) stereotactic radiosurgery (SRS) techniques to treat multiple brain metastases simultaneously can significantly improve treatment delivery efficiency, patient compliance, and clinic workflow. However, due large number of sharing the same MLC pair causing island blocking, there is higher low- intermediate-dose spillage normal dose organs-at...

PURPOSE For stereotactic radiosurgery, the AAPM Report No. 54 [AAPM Task Group 42 (AAPM, 1995)] requires the overall stability of the isocenter (couch, gantry, and collimator) to be within a 1 mm radius. In reality, a rotating system has no rigid axis and thus no isocenter point which is fixed in space. As a consequence, the isocenter concept is reviewed here. It is the aim to develop a measure...

The isocenter of the magnetic gradient fields inside a magnetic resonance imaging scanner is an important parameter in gradient non-linearity distortion correction methods for MR images. Currently there is no established method for estimating the gradient isocenter. All existing correction methods assume that the gradient isocenter coincides with the DICOM coordinate center, which is close but ...

PURPOSE To perform a quantitative study to verify that the mechanical field center coincides with the radiation field center when both are off from the isocenter during the single-isocenter technique in linear accelerator-based SRS/SBRT procedure to treat multiple lesions. METHODS We developed an innovative method to measure this accuracy, called the off-isocenter Winston-Lutz test, and here ...

A dataset range of isocenter congruency verification tests have been examined from a statistical perspective for the purpose of establishing tolerance levels that are meaningful, based on the fundamental limitation of linear accelerator isocentricity and the demands of a high-precision stereotactic radiosurgery program. Using a laser-defined isocenter, a total of 149 individual isocenter congru...

When patient anatomy is positioned away from a CT scanner's isocenter, scans of limited diagnostic value may result. Yet in some cases, positioning of patient anatomy far from isocenter is unavoidable. This study examines the effect of posi-tion and reconstruction algorithm on image resolution achieved by a CT scanner operating in a high resolution (HR) scan mode which incorporates focal spot d...

A frameless radiosurgery system is using a set of thermoplastic mask for fixation and stereoscopic X-ray imaging for alignment. The accuracy depends on mask fixation and imaging. Under certain circumstances, the guidance images may contain insufficient bony structures, resulting in lesser accuracy. A virtual isocenter function is designed for such scenarios. In this study, we investigated the i...

Single-isocenter, multitarget cranial stereotactic radiosurgery (SRS) is more efficient than using an isocenter for each target, but spatial positioning uncertainties can be magnified at locations away from the isocenter. This study reports on the spatial accuracy of two frameless, linac-based SRS systems for multitarget, single-isocenter SRS as a function of distance from the isocenter. One sy...

BACKGROUND In combined proton-carbon fixed-nozzle treatment facilities with raster scanning delivery, the scattering of proton pencil beams caused by nozzle elements and the relatively large nozzle-to-isocenter distance cause a beam broadening. This may pose limitations to the achievable dose conformity. One way to counteract this effect is by delivering the treatment in a position closer to th...