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Comment by rprospero | Hacker News Reader

My assumption is that you'd put the sensor behind the patient. After the beam has been through the body, you don't care if it's deflected or reduced.

Obviously, it's too late at that point to prevent the beam from hitting the patient, but you'll know that something went wrong and can lock the system until the problem is found.

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Many (most?) modern linear accelerators have imaging panels behind the beam path (see image [1]) which could be used for dose monitoring although they are primarily used for imaging purposes. I'm not sure whether any of these are currently used for dose monitoring.

[1] http://tommytoy.typepad.com/.a/6a0133f3a4072c970b0147e2ed7f8...

Yes, EPID panels are indeed used for dose monitoring and quality assurance of the dose delivery to the patient [1][2]. However, this is relatively new in the industry and is not universal. The fact that EPIDs have become so common (since Varian and Elekta like to offer them as standard) means that this will be used more as time goes on.

As an aside, TLDs and IVD systems are falling out of favor for patient dose monitoring because AAPM TG 62 (referenced in the link in your other post) is not directly applicable to IMRT and VMAT modalities, which are pretty common these days.

[1]http://www.sunnuclear.com/medphys/patientqa/epidose/epidose....

[2]http://www.sunnuclear.com/snc_site/solutions/patientqa/perfr...

Thanks for clarifying :)

p.s. If you are employed in Med Phys allow me to make a quick plug for my open source Med Phys QA database project: http://qatrackplus.com/

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