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Pelvis and Abdomen: R&O > Clinical Radiobiology > Flashcards

Clinical Radiobiology Flashcards

1
Q

factors which influence radio sensitivity

A

RS is proportional to reproductive rate
inversely proportional to its degree of differentiation

increases with:
increased rate of cell division
low degree of specialisation (stem cells are very RS)
high metabolic rate
increased oxygenation
increased length of time they are actively proliferating
cell cycle stage
Rs is dependent on the cell stage

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2
Q

what is radiosensitivity level

A

> 1

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3
Q

G1

A

first growth phase: cell performing normal function and growing

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4
Q

S

A

DNA replication preparing to divide
LEAST RS - contains two DNA copies

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5
Q

G2

A

second growth phase: performs normal cell fcuntions, expanding and growing

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6
Q

mitosis

A

cell divides to two cells
MOST RADIOSENSITIVE
sensitive to disruptions and is well oxygenated

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7
Q

G0

A

brain cells + spine cels are situated DONT REPLICATE
don’t have a cell cycle if they become damaged they will remain damaged

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8
Q

what phases should we target

A

G2 and m phase

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9
Q

where are the checkpoints

A

G1 & G2
if damaged will undergo cell apoptosis

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10
Q

LQM

A

SSB = rate of damage and rate at which the sub lethal damage is repaired
if it can’t be repaired it can take weeks/months depending on the cell types, which is why there’s a delay with late effects

model for cell survival determines the efficacy of the fractionation scheme

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11
Q

therapeutic ratio

A

ratio of normal tissue tolerance to lethal tumour dose

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12
Q

tumour tolerance

A

lower than normal tissue tolerance due to tumours going through the cell cycle at a slower pace taking longer to repair, more cell kill is likely to occur as they are able to hit the tumour during sensitive stages

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13
Q

TR =

A

normal tissue tol/ lethal tumour dose

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14
Q

LQM assumptions

A

DNA hits are random
probability proportional to dose
DSB needed for cell death

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15
Q

alpha =

A

DSB

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16
Q

beta =

A

SSB

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17
Q

what strand breaks are the most difficult at cell death

A

SSB, requires multiple hits

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18
Q

how are DSB produced

A

single hit by a photon = alpha
two hits by a photon, in close proximity, each breaking a single strand, producing a DSB = beta

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19
Q

clinical implications

A

early responding = high a:b
late responding = low a:b

prostate: radiation keeps causing damage, long time to respond to radiation

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20
Q

high alpha beta ratio

A

cervical
40Gy in 20 in 4 weeks or 50Gy in 25 in 5 weeks

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21
Q

low alpha beta ration

A

work best at hypo fractionated regime
60Gy in 20 fractions

22
Q

what do high ratio benefit from

A

fractionation, as it reduces normal tissue toxicity without reducing tumour lethality significantly

23
Q

what is biological effect determined by

A

total dose + treatment schedule

24
Q

what is the cervical ratio

A

10 (low fraction sensitivity)

25
Q

what is the prostate ratio

A

3/4 (slow proliferation, late reacting to radiation)

26
Q

what is the optimum conditions for cervix

A

well oxygenated to maintain Hb levels

27
Q

do SCC have fast or slow turnover

A

fast

28
Q

4R’s

A

repair: sublethal damage
repopulation: CD and population growth
reoxygenate: tumour cells often anoxic therefore radio resistant, fractionation allows for tumour cells to die, improves oxygenation for remaining cells increasing radiosensitvity
redistribution’s: each fraction the cell is in a different stage

29
Q

higher ratio

A

more linear the cell survival curve is

30
Q

lower ratio

A

the more curved the survival curve is

31
Q

what does the ratio indicate

A

how resistant a cell is to damage

32
Q

high alpha beta ratio

A

indicates that a single hit doesn’t readily accumulate to lethal effects, little increase in cell kill per unit dose for higher total dose

33
Q

low alpha beta ratio

A

that the accumulation os multiple single hits produces increased lethality for higher doses

34
Q

give a tissue with high proliferation

A

mucosa

35
Q

a tissue with slow proliferation

A

parenchyma

36
Q

what are the RT cervix requirements

A

well oxygenated
appropriate Hb
RT must be delivered within 56 days
normally SCC repopulate at a higher rate
higher radiation dose = longer treatment
CAT 1 = NO INTERRUPTIONS
may have to hyper fractionate

37
Q

late responding tissues

A

slow responding
low alpha beta
can tolerate low doses per fraction
2.7Gy - 4.9Gy
good repair capability
affected more than early responding with higher doses per fraction (hypofraction)
dose per fraction is CRITICAL

38
Q

acute responding

A

rapid proliferation
alpha beta is high
early effects seen but some recovery so cells can continue in high numbers

39
Q

CAT 1

A

SCC lung
SCC H&N
SCC cervix

40
Q

CAT 2

A

Ca endometrium
Ca prostate
sarcoma

41
Q

CAT 3

A

whole brain
spinal mets

42
Q

what does EBRT and HDR brachytherapy permit

A

repair between fractions

43
Q

biologically effective dose

A

allows for biological effects of a particular dose + fractionation scheme to be assessed

44
Q

equivalent dose

A

looks at finding an equivalent fraction to a reference scheme

45
Q

angiogenesis

A

development of blood supply
occurs in tumours >1mm
hypoxia has unfavourable clinical outcome

46
Q

hypoxia causes

A

radioresistance

47
Q

what is the iso-effective dose

A

the absorbed dose of a treatment under reference conditions providing the same biological effect in a given system as that of an actual treatment, all other conditions are the same

48
Q

BED =

A

physical dose x relative efficiency

49
Q

how can hypoxia be measured for ca cervix

A

functional MRI: provides biological information regarding the tumours physiology
improves patient care
DCA-MRI measures uptake patterns of a contrast agent
GD - CPTA uptake depends on blood transfusion: can be analysed. patterns could demonstrate a particular gene profile (hypoxia gene sets), associated with poor outcomes

advantages: MRI common, non invasive and visualises hypoxia

50
Q

what chemo drug is a sensitiser

A

cis-platin
synergistic with radiation- acute toxicity. It inhibits sublethal damage, synchronises cells to a radiosensitive phase in the cycle
reducing tumour bulk enables reoxygenation

51
Q

chemoradiation is designed for

A

patients with poor prognosis or bulky disease
IB,IIB,III, IVA disease

52
Q

pre treatment with cisplatin

A

doesn’t affect the number of DSB with rad
disrupts the repair of DSB
low doses don’t affect repair
doesn’t affect the repair of SSB

Pelvis and Abdomen: R&O (22 decks)

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