Ionising Radiation

Lower-frequency radiation is less penetrating than higher-frequency radiation, so the low frequency are preferentially absorbed compared to high- frequency radiation.

A radiopharmaceutical requires a gamma-emitting nuclide and a non- radioactive carrier to transport the radionuclide to the organ(s) of interest. Most often Tc99m (not Tc99) is used.

Isotopes are two forms of the same element that have different numbers of neutrons in the nucleus. This means same symbol, and same atomic number (subscript), but different mass number (superscript).

A compact medical linear accelerator is used to produce high-energy x-rays for radiotherapy. The other choices all involve gamma ray producing radionuclides.

The other three body parts are all named by the ICRP and have been assigned a “radiation weighting factor” determined by their known sensitivity to radiation.

The ability of x-rays to be switched off and on and to deposit enough energy within a cell to kill it makes it suitable for treatment of cancer tumours.

Radiotherapy also damages the healthy tissue through which it passes. By choosing a different path for the radiotherapy beam through the body for the next “fraction”, while at the same time ensuring that the tumour is always in the beam, allows the healthy tissue the time to recover.

If the distance doubles, the dose would be expected to decrease according to the inverse square of distance: (½)² = ¼. One quarter of 12 is 3.

Apart from the difference in how they are produced, x-rays and gamma rays are the same phenomenon.

The number of gamma photons that can pass through a medium is described by an exponential relationship. Their number decreases exponentially as the thickness increases.