Faculty Collaboration Database

Dependence of virtual wedge factor on dose calibration and monitor units. Med Phys 2001 Feb;28(2):174-7

Date

03/13/2001

Pubmed ID

11243340

DOI

10.1118/1.1344204

Scopus ID

2-s2.0-0035113291 (requires institutional sign-in at Scopus site)   12 Citations

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.

Author List

Zhu XR, Gillin MT, Ehlers K, Lopez F, Grimm DF, Rownd JJ, Steinberg TH

Author

Jason Rownd MS Instructor in the Radiation Oncology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Biophysical Phenomena
Biophysics
Humans
Particle Accelerators
Radiotherapy Planning, Computer-Assisted
Radiotherapy, Conformal
Radiotherapy, High-Energy