- When measuring data for a TPS, the following is needed: 1. output factors with and without phantom scatter (2 of Sc, Sp, Scp) 2. some sort of depth dose data (PDD) and data on absorbers (wedges)

1. Primary radiation: Dprim 2. Scattered radiation: Dscat

Contamination electrons

- Electrons are also produced in the air between the linac and patient - Contribute to surface and build-up dose - More significant in larger fields, therefore less MUs with larger fields

Factor based algorithms

- AKA 'data driven' algorithms - Based on measured data (look up tables)

Model based algorithms

- Based on a beam model with or without adjustable parameters - Approximation of reality - Used in current TPS

Parts of model based algorithms

1. Models the beams and provides a representation of the fluence distribution before the beam enters the patient 2. Models the patient based on a tomographic representation of the patient tissues e.g. RayStation: CC, Monaco: PB, CC

Intend to predict the dose delivered to the patient at any point with as much accuracy BUT: - Radiation interactions with tissues are complex - Algorithms have to be fast -> approximation - The closeness of the approximation depends on the algorithm

- Fastest - Least accurate, doesn't account for lateral scatter - Used in stage 1 of Monaco IMRT/VMAT to establish control points

- More accurate but not as accurate as MC 1. energy imparted by the primary photons: total energy released per unit mass (TERMA) 2. kernel: takes into account the scatter doses

- More complicated than photons - Side scattering is more pronounced and has more influence on the dose distribution - Can use PB and EMC

- Pretty good at predicting dose - Has problems in regions of dose homogeneity - Underestimates the effects of sharp discontinuities in density - Therefore, EMC will be increasingly used

- Stochastic integration method - Calculated quantities are subject to statistical uncertainties - Different MC codes make different assumptions to increase speed - Calcs are subject to statistical uncertainty (1% clinically)

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Algorithms

Question	Answer
TPS commissioning	- When measuring data for a TPS, the following is needed: 1. output factors with and without phantom scatter (2 of Sc, Sp, Scp) 2. some sort of depth dose data (PDD) and data on absorbers (wedges)
Components of dose	1. Primary radiation: Dprim 2. Scattered radiation: Dscat
Contamination electrons	- Electrons are also produced in the air between the linac and patient - Contribute to surface and build-up dose - More significant in larger fields, therefore less MUs with larger fields
Factor based algorithms	- AKA 'data driven' algorithms - Based on measured data (look up tables)
Model based algorithms	- Based on a beam model with or without adjustable parameters - Approximation of reality - Used in current TPS
Parts of model based algorithms	1. Models the beams and provides a representation of the fluence distribution before the beam enters the patient 2. Models the patient based on a tomographic representation of the patient tissues e.g. RayStation: CC, Monaco: PB, CC
Algorithms factors	Intend to predict the dose delivered to the patient at any point with as much accuracy BUT: - Radiation interactions with tissues are complex - Algorithms have to be fast -> approximation - The closeness of the approximation depends on the algorithm
Pencil beam	- Fastest - Least accurate, doesn't account for lateral scatter - Used in stage 1 of Monaco IMRT/VMAT to establish control points
Convolution (CC)	- More accurate but not as accurate as MC 1. energy imparted by the primary photons: total energy released per unit mass (TERMA) 2. kernel: takes into account the scatter doses
Electron algorithms	- More complicated than photons - Side scattering is more pronounced and has more influence on the dose distribution - Can use PB and EMC
PB for electrons	- Pretty good at predicting dose - Has problems in regions of dose homogeneity - Underestimates the effects of sharp discontinuities in density - Therefore, EMC will be increasingly used
MC	- Stochastic integration method - Calculated quantities are subject to statistical uncertainties - Different MC codes make different assumptions to increase speed - Calcs are subject to statistical uncertainty (1% clinically)

Created by: chloe.donaldson

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