Premium
Dynamic wedge versus physical wedge: A Monte Carlo study
Author(s) -
Shih Rompin,
Li X. Allen,
Chu James C. H.
Publication year - 2001
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1359249
Subject(s) - monte carlo method , imaging phantom , photon , physics , dosimetry , fluence , beam (structure) , electron , computational physics , wedge (geometry) , photon energy , optics , materials science , nuclear medicine , nuclear physics , mathematics , statistics , medicine , laser
The purpose of this study is to analyze the characteristics of dynamic wedges (DW) and to compare DW to physical wedges (PW) in terms of their differences in affecting beam spectra, energy fluence, angular distribution, contaminated electrons, and dose distributions. The EGS4/BEAM Monte Carlo codes were used to simulate the exact geometry of a 6 MV beam and to calculate 3‐D dose distributions in phantom. The DW was simulated in accordance with the segmented treatment tables (STT). The percentage depth dose curves and beam profiles for PW, DW, and open fields were measured and used to verify the Monte Carlo simulations. The Monte Carlo results were found to agree within 2% with the measurements performed using film and ionizing chambers in a water phantom. The present EGS4 calculation reveals that the effects of a DW on beam spectral and angular distributions, as well as electron contamination, are much less significant than those for a PW. For the 6 MV photon beam, a 45° PW can result in a 30% increase in mean photon energy due to the effect of beam hardening. It can also introduce a 5% dose reduction in the build‐up region due to the reduction of contaminated electrons by the PW. Neither this mean‐energy increase nor such dose reduction is found for a DW. Compared to a DW, a PW alters the photon‐beam spectrum significantly. The dosimetric differences between a DW and a PW are significant and clearly affect the clinical use of these beams. The data presented may be useful for DW commissioning.