Asking this question purely out of interest. I have no background in this topic.

In modern radiation therapy, there's air in between the treatment machine head and the patient. With the high levels of radiation, do we see radiation ionizing air? If so, how do we ensure the beam hasn't lost too much of its energy in air before reaching the patient

In the same vein, is this ionization the same thing as how lightning is created?


...how do we ensure the beam hasn't lost too much of its energy?

They measure it. Radiation therapy machines are calibrated using radiation detectors that are placed inside a phantom--a physical object made of material that interacts with the radiation beam in the same way that human tissue interacts with it.

Also note: Most radiation therapy is done with high-energy X-radiation or with gamma radiation. Those are not strongly attenuated by air--at least, not over the tens of cm that typically separate the source from the patient.

Skin cancers sometimes are treated with electron beams because the electrons do not penetrate much deeper than skin. In those cases, the attenuation due to air is relatively high. The distance from source to patient must be minimized, carefully measured, and the attenuation accounted for when planning the dose.

  • $\begingroup$ if you like you can consider adding proton therapy. Protons at therapeutic energy readily lose energy in air but this can be easily calculated and corrected for. $\endgroup$ – uhoh Aug 6 at 22:04

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