Radiotherapy Science Flashcards
Describe the difference between alpha, beta, and gamma rays
Alpha: A helium nucleus. Few cm range in air and is stopped by skin or a sheet of paper. It is highly ionising.
Beta: An electron. ~10cm range in air and is stopped by a few mm of aluminium. Less ionising.
Gamma: An electromagnetic wave, typically an x-ray. Infinite range in air and is stopped by a sheet of lead shielding. Least ionising.
What can be seen in an x-ray image of the rib cage (white) and the lungs (black)?
The lungs are darker because more x-rays have passed through the body to the detector without being absorbed.
What happens to an x-ray if the exposure time is increased?
It will become darker because more x-rays will penetrate the body. There is an optimal exposure at a given time but past that time the image will be less clear.
If you had a hot cup of cater and placed it in a fridge what will happen?
Initially, the hot cup of water would increase the overall temperature inside the fridge due to heat transfer from the water to the inside of the fridge but then as the fridge does work to maintain temperature, the water and the fridge will eventually cool down to the initial fridge temperature once all the heat has been dissipated.
This might increase the temperature of the room because the fridge motor will have to do more work to maintain temperature.
If a fridge door is left open with a hot cup of water in it, what will happen to the room temperature, will it increase or decrease?
The room will eventually warm up because heat travels from hot to cold environments so the inside of the fridge will warm up. The motor on the fridge will then do more work to try and cool down the fridge but in doing that it will warm up and heat the room even more.
What are the dangers of having Radon in a hospital?
Radon is radioactive. It is also colourless, odourless and tasteless so if there was a leak patients and staff could be irradiated without anyone realising.
If there was a Radon leakage, what procedures would you undertake to solve the leakage problem?
- Use a Geiger counter or similar to detect where the leak is
- Wear PPE whilst re-securing any containers
- Use a Geiger counter to detect locations with high levels of radiation and ventilate those rooms
- Ventilate any rooms containing radon incase this happens again
If a Mars bar has 280 kcal = 2.6 MJ, and a human burns energy while at rest at 80W, how long will it take to burn the mars bar at rest?
P = E / t
80W = 2.6 MJ/ t
T = 2.6 MJ/80W = 32500 s
If a Mars bar has 280 kcal = 2.6 MJ and a step is 20cm high, how many steps will it take to burn the Mars bar?
Assume all chemical energy is converted to potential energy
2.6 MJ = m g h
Assume human weight and calculate h then divide by 20cm
If an ambulance does past, why does the pitch change?
Doppler shift causes a change in frequency of the sound waves
How is Doppler used in medicine?
Doppler ultrasound: measuring blood flow
High frequency sound waves are bounced off of moving red blood cells and the frequency shift is measured.
Why are protons sometimes used over photons for therapy?
Bragg peak: they provide a greater dose relative to photons at depth
Safety to do with radiotherapy
- 1/r² law (get as far away from the machines as possible for a reduced dose)
- Short exposure times
- Shielding (e.g. the lead/concrete maze for entry into a radiotherapy room)
- In/out detectors so radiation is only targeted at the desired patient
- X-ray attenuation coefficient
Examples of lasers in medicine
- Laser eye surgery
- Calibration beams (e.g. for linacs)
Laser safety?
- Do not look directly into the source of a laser
- Cover windows/doors when in a room with an active laser
- Adequate eye protection
- Place signs outside of the room to alert people to an active laser
