What energy range is typical for X-rays used in external radiotherapy, and how are they produced?

Megavolt (MV) range energies, produced by linear accelerators rather than conventional X-ray tubes.

How do high-energy X-rays interact with atoms within cells during radiotherapy?

X-rays ionise atoms within cells.

What cellular damage results from the ionisation caused by therapeutic X-rays?

Ionisation causes DNA strand breaks.

Why does DNA damage from radiotherapy prevent cancer growth?

Damaged DNA prevents cell division, stopping the cancer from proliferating.

Why are cancer cells more susceptible to radiation damage than healthy cells?

Cancer cells divide more rapidly and have less effective DNA repair mechanisms.

AQA A-Level Physics 7408

Measurements and Their Errors

Topic overview Use of SI units and their prefixes Limitation of physical measurements Estimation of physical quantities

Particles and Radiation

Topic overview Constituents of the atom Stable and unstable nuclei Particles, antiparticles and photons Particle interactions Classification of particles Quarks and antiquarks Applications of conservation laws The photoelectric effect Collisions of electrons with atoms Energy levels and photon emission Wave-particle duality

Waves

Topic overview Progressive waves Longitudinal and transverse waves Principle of superposition of waves and formation of stationary waves Interference Diffraction Refraction at a plane surface

Mechanics and Materials

Topic overview Scalars and vectors Moments Motion along a straight line Projectile motion Newton's laws of motion Momentum Work, energy and power Conservation of energy Bulk properties of solids The Young modulus

Electricity

Topic overview Basics of electricity Current–voltage characteristics Resistivity Circuits Potential divider Electromotive force and internal resistance

Further Mechanics and Thermal Physics

Topic overview Circular motion Simple harmonic motion (SHM)Simple harmonic systems Forced vibrations and resonance Thermal energy transfer Ideal gases Molecular kinetic theory model

Fields and Their Consequences

Topic overview Fields Newton's law Gravitational field strength Gravitational potential Orbits of planets and satellites Coulomb's law Electric field strength Electric potential Capacitance Parallel plate capacitor Energy stored by a capacitor Capacitor charge and discharge Magnetic flux density Moving charges in a magnetic field Magnetic flux and flux linkage Electromagnetic induction Alternating currents Transformers

Nuclear Physics

Topic overview Rutherford scattering α, β and γ radiation Radioactive decay Nuclear instability Nuclear radius Mass and energy Induced fission Safety aspects

AstrophysicsOptional topic

Topic overview Astronomical telescope consisting of two converging lenses Reflecting telescopes Single dish radio telescopes, I-R, U-V and X-ray telescopes Advantages of large diameter telescopes Classification by luminosity Absolute magnitude, M Classification by temperature, black-body radiation Principles of the use of stellar spectral classes The Hertzsprung-Russell (HR) diagram Supernovae, neutron stars and black holes Doppler effect Hubble's law Quasars Detection of exoplanets

Medical PhysicsOptional topic

Engineering PhysicsOptional topic

Topic overview Concept of moment of inertia Rotational kinetic energy Rotational motion Torque and angular acceleration Angular momentum Work and power First law of thermodynamics Non-flow processes The p–V diagram Engine cycles Second Law and engines Reversed heat engines

Turning Points in PhysicsOptional topic

Topic overview Cathode rays Thermionic emission of electrons Specific charge of the electron Principle of Millikan's determination of the electronic charge, e Newton's corpuscular theory of light Significance of Young's double slits experiment Electromagnetic waves The discovery of photoelectricity Wave–particle duality Electron microscopes The Michelson-Morley experiment Einstein's theory of special relativity Time dilation Length contraction Relativistic mass and energy

ElectronicsOptional topic

Topic overview MOSFET (metal-oxide semiconducting field-effect transistor)Zener diode Photodiode Hall effect sensor Difference between analogue and digital signals LC resonance filters The ideal operational amplifier Inverting amplifier configuration Non-inverting amplifier configuration Summing amplifier configuration Real operational amplifiers Combinational logic Sequential logic Astables Principles of communication systems Transmission media Time-division multiplexing Amplitude (AM) and frequency modulation (FM) techniques

Medical Physics

Use of high-energy X-rays

3 things to know
Paper 3, section B

Overview

External radiotherapy, why the source is rotated, and why cancer cells are more vulnerable.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What energy do therapeutic X-rays use, and what damage do they cause in cells?

Evaluation

Why is the source rotated around the patient, and why are cancer cells more vulnerable?

Numbers

How do high-energy therapeutic X-rays compare with diagnostic X-rays in terms of penetration and dose distribution?

Questions from this subtopic

Each one with the model answer underneath.

1
What energy range is typical for X-rays used in external radiotherapy, and how are they produced?
Model answer
Megavolt (MV) range energies, produced by linear accelerators rather than conventional X-ray tubes.
2
How do high-energy X-rays interact with atoms within cells during radiotherapy?
Model answer
X-rays ionise atoms within cells.
3
What cellular damage results from the ionisation caused by therapeutic X-rays?
Model answer
Ionisation causes DNA strand breaks.
4
Why does DNA damage from radiotherapy prevent cancer growth?
Model answer
Damaged DNA prevents cell division, stopping the cancer from proliferating.
5
What is the ultimate outcome for cancer cells that sustain sufficient radiation-induced DNA damage?
Model answer
Cancer cells are destroyed.
6
Why are cancer cells more susceptible to radiation damage than healthy cells?
Model answer
Cancer cells divide more rapidly and have less effective DNA repair mechanisms.

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