In recent radiation therapy, the electronic portal imaging device (EPID) is significant as a quality assurance (QA) tool for intensity modulated radiation therapy (IMRT). Some QA software for delivered dose verification is commercially available. Such software can compare images of actually delivered fluence and predicted image by convolution of planned fluence distribution and point spread function in EPID. Only single spread function is usually provided for an accelerate potential, and it is adjusted to get a good agreement between predicted image and actual EPID image of the reference field. However, variation of photon energy spectrum between the IMRT and the reference field can be expected because the IMRT fields consist of various segmented fields and off-set fields. Therefore, this study investigates photon energy response of EPID and develops a method to correct for energy dependence of EPID response. To investigate the response of EPID for photon, the point spread functions in EPID for several mono energies were calculated by Monte Carlo simulation. As a result, it is obvious that the variation of point spread function is negligible for energy. However, the energy absorption in phosphor layer varied with photon energy. Therefore, the EPID image can be predicted by convolution of planned fluence distribution and point spread function which is corrected with local energy spectrum. And it is confirmed that the predicted image well agreed with actual acquired image.
|Number of pages||5|
|Publication status||Published - 2008 Dec 1|
|Event||15th EGS Users' Meeting in Japan 2008 - Tsukuba, Japan|
Duration: 2008 Aug 6 → 2008 Aug 8
|Other||15th EGS Users' Meeting in Japan 2008|
|Period||08/8/6 → 08/8/8|
ASJC Scopus subject areas