Dosimetry 4 Flashcards
1
Q
What is In-Vivo dosimetry?
A
- Used on or near the patient
- Used to verify the treatment plan
- Can be relative or measure a dose in Gy
2
Q
How do the semi-conductor diodes work?
A
- used In-Vivo
- Ionising particles (E- produced in interactions)
- Small potential difference across the depletion layer means positive charges are drawn toward the negative and vice versa.
- Creates flow of charge which is measured.
- More dose = more charge
3
Q
How do photon/electron diodes differ?
A
- Photons have a thicker build up cap
- Electrons mostly have a very thin build-up cap
4
Q
What are the advantages of diodes?
A
- Higher relative sensitivity than an ionisation chamber
- They have a fast response time
- Small in size
- good mechanical stability
- doesnt require pressure corrections for reading
5
Q
What are the disadvantages of diodes?
A
- Has temperature dependence
- Has an energy, doserate and angular dependence
- Requires electrical connection wires
- Response can change over time
6
Q
What is MOFSET?
A
- Metal Oxide Semiconductor Field Effect Transistor
- Capable of dose measurements immediately after irradiation or can be sampled in predefined time intervals
- Operates in both active and passive
mode - Implantable versions exist
7
Q
What are MOSFET correction factors?
A
- Environmental (temperature only, not for pressure)
- Energy dependence ( beam energy, modality)
- Accumulated dose
- Dose rate
- Field size
- SSD
- Directional dependence
