Assessing focal spot alignment in clinical linear accelerators: a comprehensive evaluation with triplet phantoms.

A fundamental parameter to evaluate the beam delivery precision and stability on a clinical linear accelerator (linac) is the focal spot position (FSP) measured relative to the collimator axis of the radiation head. The aims of this work were to evaluate comprehensive data on FSP acquired on linacs in clinical use and to establish the ability of alternative phantoms to detect effects on patient plan delivery related to FSP. FSP measurements were conducted using a rigid phantom holding two ball-bearings at two different distances from the radiation source.

Curvature correction factors for the independent verification of monitor units of electron treatment plans calculated in Eclipse.

Electron beam dosimetry is sensitive to the surface contour of the patient. Over 10% difference between Treatment Planning System (TPS) and independent monitor-unit (IMU) calculations have been reported in the literature. Similar results were observed in our clinic between Radformation ClearCalc IMU and Eclipse TPS electron Monte Carlo (eMC) algorithm (v.

Beam focal spot intrafraction motion and gantry angle dependence: A study of Varian linac focal spot alignment.

The characteristics of the focal spot of the linear accelerator (linac) play a role in determining the resulting dose distribution within the patient, and hence probability of treatment success. A direct measurement of focal spot position is not recommended by AAPM Task Group 142, but factors influenced by focal spot position, such as beam symmetry and isocentre position, are. Traditional methods of measuring focal spot position are time consuming and can only be performed at gantry 0°.