Measurement Timing in Beamchecker

[member_2851]

Hi,

I'm trying to baseline our beamchecker for use on Tomotherapy. I've included blocks in the tomo plan to prevent dose being delivered through the sides of the detectors (as advised in the manual). However this means most/all MLCs are closed for part of the gantry rotation and so the Beamchecker assumes the measurement has finished and stops recording.

Is there any way to set a longer measurement time in the software to prevent this happening?

[Chris]

Hello,

The timeout window for exposure in the Tomo dynamic mode is about 2 seconds, so depending on the delivery parameters this can certainly occur. I would recommending either increasing rotation speed (if possible), or narrowing the blocking region.

If neither option is possible in this case, generally any variability caused by beam delivery parallel to the chamber surface will be very small, and there are customers who do no blocking without any issues.

Finally to the original question, this timing cannot be adjusted, but this is something I will note for us to consider for a future software update. At the very least, we can look at extending this time window to a new standard value. Roughly how long does the delivery pause during the blocking regions of your current plan?

Thanks for your message.

[member_2851]

Thanks for your help Chris. I've tried it now without any blocking and it seems to work fine.
I think with the blocking as recommended in the manual (chamber sides + 10-15 degrees) and the gantry moving at full speed i think the beam off time was around 2 seconds. Which is what confused me at first, as it wouldn't always stop the measurement in the same place. I think increasing it to 3 or 4 seconds would solve this problem, but I suppose more complex plans may cause the grantry to move more slowly.