<div dir="ltr"><div>Hi Luke,<br>I would suggest to check if there are elements in the beam other than the collimator that might scatter. For example, is the beam filtered ans do you model these filters in your Gate simulation?<br></div><div>Except an element causing scatter or a too thick collimator, I have no other suggestions...<br></div><div>Good luck!<br></div><div>Simon<br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Mar 28, 2018 at 8:16 AM, Luke Gilling <span dir="ltr"><<a href="mailto:Luke.Gilling@waikatodhb.health.nz" target="_blank">Luke.Gilling@waikatodhb.health.nz</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal">Hello all,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I am a MSc thesis student working in a radiotherapy department in New Zealand. As part of my research I am simulating the relative dose output in water from a diagnostic x-ray tube in GATE. My source is a ‘UserSpectrum’ energy type and
the spectral data is based on a standard tungsten anode. Downstream of my source is various collimators and filtration (distances from source and materials all defined by the manufacturer).<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I have 3 dose actors in my water phantom (which is a simple cube of water). One measures the depth dose/PDD and the other 2 measure dose across the beam (x and y profiles). My simulated PDD matches quite well (within 5%) with measured data
but the profile data is not matching well. I’ve attached a figure for a 10 x 10 cm profile here. You can see that the MC simulated profile does not match those measured with ion chamber and gafchromic film under the same conditions. The beam penumbra is not
wide enough and the scatter in the tails of the profile is too low.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Assuming my user input spectrum is correct <i>does anyone have suggestions on how I can improve the match between my simulated and measured data</i>?
<u></u><u></u></p>
<p class="MsoNormal">I have attempted to increase my source size and also to adjust my collimation settings with no success.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><b><span style="color:#1f497d">Luke Gilling<u></u><u></u></span></b></p>
<p class="MsoNormal"><span style="color:#1f497d">Medical Physics Registrar<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d">Lomas Building | Waikato Hospital | Waikato DHB<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d" lang="EN-US"><a href="tel:+64%207-839%208899" value="+6478398899" target="_blank">+64 7 839 8899 x 98242</a><u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d" lang="EN-US"><a href="tel:+64%2027%20364%202563" value="+64273642563" target="_blank">+64 27 364-2563</a><u></u><u></u></span></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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