Wk12 Treatment Planning Systems

Question 1

What is the importance of calculation algorithms in treatment planning systems?

Answer 1

• responsible for the correct representation of dose in the patients
• results of dose calculations are frequently linked to beam-time or monitor unit calculations
• many clinical decisions are taken on the basis of the calculated dose distributions.

Question 2

What is primary radiation and scattered radiation?

Answer 2

Primary radiation:
= radiation incident on the surface
= include photons coming directly from the source as well as radiation scattered from structures and collimators

Scattered radiation:
= from interactions of the primary radiation with the phantom (patients)

Question 3

What calculation method decompose a radiation into primary and scattered component?

Answer 3

Convolution-superposition method model
= primary photon interaction is separated from scattered photons and charged particles through photoelectric effect, Compton scattering and pair production

Question 4

What are the roles of a simulator

Answer 4

1. Localisation of treatment field / tumour or vital organs / implanted or inserted radioactive sealed source
2. Simulation and set up verification
   3.skin marking
3. Monitor progress of treatment
4. Simple diagnosis of disease
5. Ascertain required treatment position eg. Screen before mould
6. Fluoroscopy-guided biopsy

Question 5

What are features of CT simulator?

Answer 5

• movable ceiling and lateral lasers
• large bore CT
• flat couch top

Question 6

What are the roles of a CT simulator?

Answer 6

• scanning patients under treatment position
• localisation of tumour and OAR
• calculation of radiation dose
• provide reference image for treatment verification eg. OBI, CBCT, MVCT

Question 7

What is 4DCT?

Answer 7

• to capture the shape and trajectory of moving organs during respiration
• the abdominal surface (surrogate signal) is recorded to form the curve of respiratory phase
• repeat capture of images on the same slice position is saved into computer
• the CT images are sorted according to the surrogate signal

Question 8

Name some common surface guided system

Answer 8

Catalyst

Question 9

How do surface guided system works?

Answer 9

• make use of cameras consist of 2 components: a LED projector and a CCD camera
• the CCD camera captures the reflected LED light from the patients’ surface to form a 3D surface model
• the software calculates a 6D shift vectors to correct patient setup