Radiation Therapy: Dosage, Duration & Effects

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Discussion Overview

The discussion revolves around the differences in radiation exposure between radiation therapy for cancer treatment and the radiation from a nuclear explosion. Participants explore the implications of dosage, duration, and the focus of radiation delivery in therapeutic contexts versus catastrophic events.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that cancer patients may receive 170-190 rads of radiation daily for 7-9 weeks, comparing this to the radiation exposure at 1 mile from a Hiroshima explosion, questioning the differences in effects due to duration and area covered.
  • Another participant suggests that fear of radiation has historical roots in Cold War propaganda, implying that the dangers of radiation exposure were overstated compared to the immediate effects of a nuclear blast.
  • A participant explains that radiation therapy targets tumors using imaging techniques, but acknowledges that healthy tissue is also affected, as no current technology can isolate cancerous tissue completely.
  • Further, it is mentioned that treatment areas are often set larger than the tumor to account for movement, which leads to additional healthy tissue being irradiated.
  • One participant inquires about the ViewRay system, asking how real-time imaging with MRI ensures that the radiation beam is accurately targeting the tumor, and whether there is a feedback system for the radiation delivery.
  • A technical detail is provided about the Multi Leaf Collimator (MLC), which shapes the target area and reduces radiation exposure outside the target zone.

Areas of Agreement / Disagreement

Participants express varying views on the implications of radiation exposure, with some focusing on the technical aspects of radiation therapy and others discussing historical perspectives on radiation fear. There is no consensus on the broader implications of these differences.

Contextual Notes

The discussion includes assumptions about the effectiveness and limitations of current radiation therapy technologies, as well as the historical context of public perception regarding radiation exposure. Specific technical details about treatment methodologies are also mentioned without resolving their efficacy or implications.

nesp
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Not sure if this belongs here or in the nuclear engineering forum.

Many cancer patients in radiation therapy for cancer receive as much as 170-190 rads of daily radiation for 7-9 weeks. When I looked at a radiation chart I found that equates roughly to the dose at 1 mile from a Hiroshima type explosion on a daily basis. The former is, hopefully, curartive. The latter is, presumably, lethal.

What's the difference? Is it the duration? Milliseconds for a nuclear blast vs minutes for radiation therapy? Or is it area covered? Whole body for nuclear blast vs focused for radiation therapy?
 
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I think this fear of radiation was in a large part cold war propaganda to reduce the fear of a nuclear attack you weren't going to blown to bits or burnt to death as most of the victims at Hiroshima were but the main danger was RADIATION that could be stopped by some newspapers covering the windows.
 
To answer your question, yes, it is whole body vs focused radiation. Treatment plans involve using some kind of imaging (MRI,CT, etc.) to locate the tumor, then the physician prescribes a treatment area which includes the tumor site. Unfortunately, there is healthy tissue around the tumor, and no device can currently target only cancerous tissue. So the physician sets the treatment area to slightly larger than the tumor area so as to make sure the tumor is irradiated while as much as possible limiting the irradiation of healthy tissue. Depending on the device, treatments areas can focus radiation to 1mm or even less.

The main problem with this is that the tumor can move between or during treatment (depending upon body location), so the doctor usually sets the treatment area to several centimeters larger than the tumor area, and even more healthy tissue gets irradiated. [Blatant plug here] ViewRay has received FDA clearance for a device that uses MRI for real time imaging of the tumor, which could potentially reduce the area that needs irradiation.
 
davep, thanks for the reply.

So with something like that view ray system, the targeted area is visualized real time as it's being radiated? And it's done with MRI?

I assume the MRI is used to detect movements of the tumor being targeted. How do you know that the linear accelerator is depositing its energy at precisely the targeted area? Is there a separate feedback system for the radiation beam?

It's amazing that the beam can be focused to mm precision.
 
The MLC (Multi Leaf Collimator) defines the target area shape, and the MLC attenuates the beam outside the target area to a fraction of the dose delivered to the target area.
 

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