Can radiography with gamma rays be used in medicine? If not, why not?
Is it a technical issue (gamma rays are not easy to generate or detect for this purpose) or is it a safety issue (gamma rays are too dangerous)?
X-rays and gamma radiation are both types of electromagnetic radiation. X-rays originate from outside the nucleus of an atom (interactions of electrons), whereas gamma radiation originated in the nucleus of the atom as part of radioactive decay. Gamma radiation is (by definition) of higher energy and shorter wavelength than x-ray radiation. Both have wavelengths shorter than visible light.
Gamma rays are more penetrating and more ionising than x-rays, so they have more potential to cause cellular damage; a feature that is useful in radiotherapy applications (though both x-rays and gamma rays are used for this).
Gamma radiation is widely used in medical imaging and treatment. This usually comes under the remit of a nuclear medicine department.
Radioisotopes that emit gamma radiation can be injected and gamma cameras used to record uptake in the body. Different radioisotopes are taken up to varying amounts by different organs.
Gamma radiation (and other types, such as neutron beams) are used in radiotherapy, as part of the treatment for cancer.
For example, gamma knife surgery is a very precise stereotactic gamma radiotherapy used for certain brain tumours.
Another example is that radioactive iodine is preferentially absorbed by the thyroid gland and is used to treat certain types of hyperthyroidism and thyroid cancer. The related MIBG scan can also be used for other diagnostic purposes, including pheochromocytoma.