Direct measurement of ion chamber correction factors, < i > k < /i > < sub > Q < /sub > and < i > k < sub > B < /sub > < /i > , in a 7 MV MRI-linac.

In this study, for the first time, both &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;Q&lt;/sub&gt; and &lt;i&gt;k&lt;sub&gt;B&lt;/i&gt;&lt;/sub&gt; were measured directly for 6 waterproof ion chambers (3 × PTW 30013 and 3 × IBA FC65-G) in a pre-clinical 7 MV MRI-linac at 0 T and at 1.5 T. Measurements were done with the only available primary standard build for this purpose, a water calorimeter. Resulting &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;Q&lt;/sub&gt; factors for PTW and IBA chambers were respectively 0.985(5) and 0.990(4). &lt;i&gt;k&lt;sub&gt;B&lt;/i&gt;&lt;/sub&gt; factors were measured with the chambers in antiparallel direction to the magnetic field (|| 180°), and perpendicular direction (┴ 90°). &lt;i&gt;k&lt;sub&gt;B&lt;/i&gt;||&lt;/sub&gt; and &lt;i&gt;k&lt;sub&gt;B&lt;/i&gt;┴&lt;/sub&gt; for the PTW chambers were respectively 0.985(6) and 0.963(4) and for IBA chambers 0.995(4) and 0.956(4). Agreement with the available literature values was shown, partly caused by the relatively large standard deviation in those values. The values in this study are currently the only available measured values for &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;Q&lt;/sub&gt; and &lt;i&gt;k&lt;sub&gt;B&lt;/sub&gt;&lt;/i&gt; in an MRI-linac that are directly l...

Source: Physics in Medicine and Biology - March 31, 2019 Category: Physics Authors: de Prez LA, Woodings SJ, de Pooter JA, van Asselen B, Wolthaus JWH, Jansen BJ, Raaymakers BW Tags: Phys Med Biol Source Type: research