Questions and Answers
Who discovered X-rays?
Roentgen
Which type of radiotherapy unit initially gained prominence after the invention in the early 1950s?
What are the two groups of X-ray photons produced during radiotherapy?
All modern radiotherapy uses cobalt units exclusively.
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In which energy range do clinical X-ray beams typically operate?
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What event leads to the production of characteristic X-rays?
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Characteristic X-rays are emitted when an _____ electron fills an orbital vacancy.
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What is the fluorescent yield (w)?
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Study Notes
Introduction to Radiotherapy Technology
- Radiotherapy began shortly after X-ray discovery by Roentgen in 1895, initially focusing on increasing photon and electron beam energies.
- Early technological advancements were slow, primarily using X-ray tubes, van de Graaff generators, and betatrons.
- The 60Co teletherapy unit, invented by H.E. Johns in the 1950s in Canada, significantly advanced radiotherapy by providing higher photon energies.
- Medical linear accelerators (linacs) replaced cobalt units, evolving through five generations and becoming the primary radiation source in modern therapy.
- Linacs are compact, efficient, versatile, and can deliver both electron and megavoltage X-ray therapy with a wide energy range.
- Alternative accelerators such as betatrons and microtrons are also used, along with special particles like protons and heavy ions, though linacs and cobalt units dominate.
X-ray Beams and X-ray Units
- Clinical X-ray beams vary in energy from 10 kVp to 50 MV, produced by decelerating electrons in metallic targets.
- The majority of the electron's kinetic energy converts to heat in the target, with a small portion emitted as X-ray photons.
- X-ray photons can be categorized into two main types: characteristic X-rays and bremsstrahlung X-rays.
Characteristic X-rays
- Characteristic X-rays originate from Coulomb interactions between incident electrons and target material’s atomic orbital electrons.
- When an incident electron collides with an orbital electron, it ejects the orbital electron, creating a vacancy.
- Another electron from a higher energy shell fills this vacancy, leading to the emission of energy in the form of a characteristic photon or an Auger electron.
- The fluorescent yield (w) quantifies the number of characteristic photons emitted per vacancy (0 < w).
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Description
Test your knowledge on treatment machines for external beam radiotherapy as discussed in Chapter 5. This chapter covers the advancements in technology since the discovery of X-rays and their impact on radiotherapy practices. Engage with the material and solidify your understanding of the subject.
