RT-theory

Question 1

What kind of radiation beams can be produced by a Linear accelerator?

Answer 1

High energy x-ray and electron beams

Question 2

What kind of radiation is brachytherapy?

Answer 2

It uses I131 and produce beta-particles (electrons and positrons)

Question 3

High-energy beams (photons) deposit energy ______

Answer 3

at a greater depht than eletrons

Question 4

Low-energy beams (electrons) deposit most of the energy_______.

Answer 4

Skin surface

Question 5

Name the 3 processes by which x-ray photons give up their energy when interacting with tissue?

Answer 5

Photoelectric effect, compton effect, paired reduction

Question 6

What is the definition of Gy?

Answer 6

1 Gy = 1 J/kg (1 joule absorbed per kg)

Question 7

Define LET?

Answer 7

Linear energy transfer = average energy lost by a particle over a given track length

The biologial effect of a dose of radiation depends on its LET

Question 8

Give an example of a low LET particle and a high LET particle?

Answer 8

low = photons
high = protons

Question 9

How can DNA be damaged by radiation?

Answer 9

Direct - absorption of energy by DNA
Indirect- damage via free radicals

Question 10

Which radical is most damaging for DNA

Answer 10

Hydroxyl radixal - oxidising

Question 11

How many doble strand breaks are achieved pr. 1Gy?

Answer 11

only 25-50

Question 12

What is mitotic cathastrophy?

Answer 12

Occur due to chromosomal aberrations secondary to DNA DSB

Question 13

What is the bystander effect?

Answer 13

When ROS or other factors are released from irradiated cells, causing damage to nearby non-irridated cells

Question 14

By which two mechanisms can DNA DSBs occur and what are they called?

Answer 14

Passage of sinfle paricle = linear effect - seen most with low dosages

Passage of two separat particles causing a SSB = quadratic component - high dose

Question 15

What is the alpha-beta ratio?

Answer 15

Its where the killing via the one hit(linear) and two hit (quadratic) kinetics are equal

Question 16

Which tumours are considered to have a low a/b ratio?

Answer 16

melanoma, prostatic tumour, STS, TCC, OSA

Question 17

By which modes can a cell die after RT and which one is most common?

Answer 17

Apoptosis, necrosis, miotic cathastrophe (most common), terminal growth arres

Question 18

Which 4 cell types are particularly sensitive to apoptotic death?

Answer 18

Lymphocytes
Thymocytes
Salivary gland epithelium
Spermatozoa

Question 19

Where in the cell cycle are the cells most senistive to radiaion?

Answer 19

M-phase (and late G2)

Question 20

Why are cells in S-phase more resistant to radiation?

Answer 20

Due to increasd DNA repair in this phase

Question 21

Which drugs can increase radiosensitisation?

Answer 21

Imatinib
PARPi
Carboplatin
Gemcitabine

Question 22

Defnine the following:
CRT
3D-CRT
IMRT
SBRT
Brachy
Plesio

Answer 22

CRT- uniform intensity across the RT beam, square
3D-CRT - uniform intensity, irregular beam shape
IMRT - variying intensity of the beam, irregular shape
IGRT - IMRT which changes the size shape and location of tumour or other organs
SBRT - highly conformal, often RT administered in 1-5 fractions
Brachy - directly adjacent tumour or within
Plesio - source of RT placed in contact with exterior surface of the body

Question 23

GTV

Answer 23

Gross tumour volume

Question 24

CTV

Answer 24

Clinical target volume - allows for tx of microscopic disease beyond edge of visible tumour, or metastatic disease

Question 25

PTV

Answer 25

Planned target volume - GTV + CTV + additional margin for set up error, patient movement etc

Question 26

By which cellular mechanisms are DSBs repaired?

Answer 26

Homologous recombination - S and G2 Non-homologous end joining - throughout cell cycle

Question 27

What are the risks of SRT?

Answer 27

Higher risk of late effects due to high dose in few fractions - it is fractionation and allowing repair which spares the normal tissues

Question 28

What are the reasons combining RT with other treatments may improve outcome?

Answer 28

1. Prevent repopulation 2. Decrease clonogenic tumour cells 3. Increase cellular rt sensitivity 4. Improve reoxygenation 5. Kill circulating endothelial precursor cells which would replace vasculature destroyd during RT.

Question 29

Name 5 factors impacting tumour senistivity to RT

Answer 29

1. Number of CSC - increased nr = increased RT dose needed 2. Degree tumour hypoxia 3. Genetic/epigenetic heterogeneity 4. Degree of expression/acivation of intracellular pathways (EGFR/MEK/ERK adn PI3K/AKT) 5. Vascular damage - pro (deprivation of nutrients and cell death con increased hypoxia

Question 30

What is the beneficial effect of hypoxia?

Answer 30

The biological effect of RT are enhanced by oxygen Oxygen can fix the DNA damage caused by hydroxyl radicals and lead to irreparable damage.

Question 31

What are the drugs nimorazole and tirapazamine?

Answer 31

Hypoxic cell senzitiser Drug toxic ony to hypoxic cells

Question 32

When is the cut of between early, early delayed and delayed responses for RT?

Answer 32

Acute - less than 3 in rapidly dividing cells Early delayed - 2 w and 4 months (only neurological tissue) Late response - over 3 months in slowly dividing cells

Question 33

What are consequential late effects?

Answer 33

When severe early reactions result in impaired tissue recovery

Question 34

Which factor influence the risk of acute tox the most?

Answer 34

By the time over which a protocol is administered (and total dose)

Question 35

Which factors impact the risk of late tissue tox the most?

Answer 35

Fraction size, volume of tissue irradiated and total dose

Question 36

What are functional subunits?

Answer 36

How one consider some late responding tissues - arranged in parallel (lung, liver, kidney) or series (spinal cord, intestine)

Question 37

Is it parallel or series tissue which have a reserve capasity when it comes to late RT effect?

Answer 37

Parallel

Question 38

What is amifostine?

Answer 38

Drug that can be used to reduce sensitivity of normal cells to RT, without influencing tumour cll sensitivity

Question 39

What are the 5 Rs of radiation

Answer 39

Repair Repopulation Reoxygenation Redistribution Radiosensitivity

Question 40

Hyperfractionated

Answer 40

o Involves giving a larger total dose o Fraction size reduced; number of fractions increased o Treatment time is the same o Allows higher tumour control (due to higher total dose), whilst reducing late toxicity

Question 41

What is BED used for?

Answer 41

A calculation used to predict how changes in dose prescription may affect different cells/tissues based on their alpha/beta ratio