4 ms·

Agree and also would of thought they would have a sensor on patient that measures dosage independently of the system giving the dosage. But from what I can tel

• Someone1234 11y ago
  How would you sense that without risking either deflecting the beam (which could cause harm/cancers in other body parts) or reducing the beam's intensity (which could cause treatment to be less effective). This is one of those ideas that sounds a lot easier than it likely is.
  • rprospero 11y ago
    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.
    • randlet 11y ago
      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/6a0133f3a4072c970b0147e2ed7f81970b-800wi http://tommytoy.typepad.com/.a/6a0133f3a4072c970b0147e2ed7f8...
      • FiatLuxDave 11y ago
        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.asp http://www.sunnuclear.com/medphys/patientqa/epidose/epidose.... [2]http://www.sunnuclear.com/snc_site/solutions/patientqa/perfraction http://www.sunnuclear.com/snc_site/solutions/patientqa/perfr...
        • randlet 11y ago
          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/ http://qatrackplus.com/
  • randlet 11y ago
    Putting things in the way of the beam to measure dose is actually quite common. You can do real time dose monitoring using diodes (see [1]). The diodes are quite small and don't generate huge amounts of scatter. It is quite common to use TLD's[2] to monitor patient dose which is then analyzed offline to give dose estimates after the fact. edit: that said, I don't think anybody was doing real-time in-vivo measurements during the era of the Therac incident. [1] https://www.aapm.org/pubs/reports/RPT_87.pdf https://www.aapm.org/pubs/reports/RPT_87.pdf [2] TLD=thermoluminescent dosimeter, little hunks of metal whose electrons get stuck in an excited state when exposed to radiation, you then heat them up and measure the light they give off as they relax back to ground state. The amount of light they give off can then be correlated with the dose the patient received.
  • Zenst 11y ago
    Well as most dosage is focused, you just increase that area to include the sensor. WIth such focused exposures you have shielding for the patient for the parts you do not wish to radiate and with that just place the sensor upon that and not impacting dosage upon patient at all. That's how I'd do it from my understanding of the usage practices today.
    • randlet 11y ago
      Shielding a patient like this isn't really feasible. The half-value-layer of lead in a 6MegaVolt clinical beam is 17mm [1]. That is, even with nearly an inch of lead shielding in place you'd still be delivering a large dose of radiation to healthy tissue. [1] https://quizlet.com/4622164/hvl-layers-flash-cards/ https://quizlet.com/4622164/hvl-layers-flash-cards/