<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi Chris, <div class=""><br class=""></div><div class="">1. You should change the geometry of world volume because it should be<span style="font-size: 13px;" class=""> large enough to include the entire simulation geometry. The tracking of any particle</span></div><div style="margin: 0px; font-size: 13px; line-height: normal;" class="">stops when it escapes from the world volume. In your macro, I suggest you to increase X, Y and Z lengths not less than 250 mm ( you have phantom sphere radius of 125 mm, so length should be greater than diameter of spherical phantom). Checking with visualization wouldn’t be a bad idea to understand whats going on inside the world geometry. It might be the reason of discrepancy. </div><div style="margin: 0px; font-size: 13px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal;" class="">2. I encourage you to check the best physics list mechanism based on the your Gate version and Geant4 version. For example: Geant4 10.3 version has emstandard_opt3 physics list EM constructors which was designed for applications that require higher accuracy of electrons ( as in dosimetry) and add Rayleigh scattering process for low energy electrons.</div><div style="margin: 0px; font-size: 13px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal;" class="">3. For dose actor definition: you are supposed to put any 2 combination, for example: you can define voxel size and resolution, or voxel size and Size, or resolution and Size. Gate automatically calculates the third parameter for you. </div><div style="margin: 0px; font-size: 13px; line-height: normal;" class=""><span style="white-space: pre-wrap; background-color: rgb(255, 255, 255);" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-size: 13px; white-space: pre-wrap; background-color: rgb(255, 255, 255);" class="">4. For dose accuracy of beta emitters, say P-32, you are supposed to simulate the whole beta spectra. Google nuclear database (</span><font size="2" class=""><span style="white-space: pre-wrap;" class="">e.g.; Nudat) and pull out beta spectrum information and use it to define the discrete spectrum. I’m attaching spectrum of P-32 in the following lines:</span></font></div><div style="margin: 0px; line-height: normal;" class=""><font size="2" class=""><span style="white-space: pre-wrap;" class=""><br class=""></span></font></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">#### P-32 beta spectrum #####</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1<span class="Apple-tab-span" style="white-space:pre"> </span>0</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.0428 3.03E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.1283 4.38E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.2138 5.50E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.2994 6.43E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.3849 7.17E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.4704 7.70E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.5559 8.02E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.6414 8.11E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.7270 8.00E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.8125 7.68E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.8980 7.16E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">0.9835 6.48E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.0690 5.66E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.1546 4.74E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.2401 3.76E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.3256 2.78E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.4111 1.85E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.4966 1.03E-02</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.5822 4.09E-03</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">1.6677 8.09E-04</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class="">If you do not know the meaning of 1 and 0 in the above spectrum then read the Gate manual carefully.</div></div><div class=""><br class=""></div><div class="">I hope this helps.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Regards, </div><div class="">Ashok Tiwari</div><div class=""><br class=""></div><div class=""><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal;" class=""><br class=""></div></body></html>