Abstract
One of the important features of the Siemens Virtual Wedge (VW) is that the VW factor (VWF) is approximately equal to unity for all beams with a total deviation for a given wedge no greater than 0.05, as specified by Siemens. In this note we report the observed dependence of VWF on dose calibration (cGy/MU), monitor units (MU), and beam tuning for a Primus, a linear accelerator with two dose-rate ranges available for VW operation. The VWF is defined as the ratio of doses measured on the beam central axis for the wedge field to the open field; the open field dose is always measured with the nominal high dose-rate beam. When VW operates in the high dose-rate range, the VWF is independent of calibration (cGy/MU). When VW works in the low dose-rate range, the VWF varies linearly with the calibration of the low dose-rate mode. For a linear accelerator that has only one dose-rate range for VW, there is no observable dependence of VWF on the calibration. We also studied the monitor unit dependence of VWF. A discontinuity in VWF was observed at the switching point between the high and low dose-rate ranges. Working with Siemens, we have investigated causes of this discontinuity. As a result of this investigation, the discontinuity in VWF as a function monitor unit is practically removed.
Original language | English (US) |
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Pages (from-to) | 174-177 |
Number of pages | 4 |
Journal | Medical physics |
Volume | 28 |
Issue number | 2 |
DOIs | |
State | Published - 2001 |
Keywords
- Virtual wedge
- Virtual wedge factor
ASJC Scopus subject areas
- Biophysics
- Radiology Nuclear Medicine and imaging