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MRSC 2501 > Brachy > Flashcards

Brachy Flashcards

1
Q

Are sources sealed or unsealed?

A

sealed

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2
Q

What is dose homogeneity

A

Some parts of tumour will receive much high dose than other parts.

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3
Q

4 Methods of classifying Brachy

A

Treatment Duration
Dose rate
Radioactive source placement
Loading method

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4
Q

What dose rate is used for permanent brachy seeds?

A

Low Dose Rate

LDR

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5
Q

Which dose rates would the radioactive source have a long half life and why?

A

HDR as the dose rate would be more ‘steady’ due to the longer falloff times for radioactive decay.

Remember that in HDR the source will be removed afterwards.

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6
Q

Which LDR radioactive source is traditionally used ? and which has better radiobiology?

A

Traditionally used: Iodine - 125

Radiobiology: Cesium 131

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7
Q

Commonly used HDR source?

A

Iridium 192

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8
Q

What type of decay is preferable for Brachy?

A

No charged particle emission

( beta particle emission can however be filtered out).

no radioactive daughter product

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9
Q

Approximately what is the decay energy of Ir-192

A

0.4 meV

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10
Q

What is the approximate energy of the isotopes commonly used in low dose rate
(LDR) brachytherapy?

A

30 keV

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11
Q

What is the SI unit for source strength?

A

Air kerma rate (μGy h-1 m2)

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12
Q

Why is the source measured in radioactive per gram?

A

Amount of radiation given out per gram.

This is because we need a high level of radioactive in a small substance so it can fit in the needle.

It also needs to be non toxic and easily shaped.

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13
Q

Where is permanent brahy treatments traditionally placed?

A

interstitial

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14
Q

intraluminal

A

Into oesophagus, bronchus.

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15
Q

vascular

A

Into blood vessels

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16
Q

What type of loading is used in LDR?

A

Manual Afterloading

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17
Q

Which term SHOULD be used in Brachy when referring to radioactive decay of the source?

A

Source strength as it uses the air kerma rate as its SI

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18
Q

H 1/2 of Iodine 125

A

60 days

19
Q

H1/2 of most LDR isotopes

A

74.2 days

20
Q

Is a mono or poly energetic source preferred?

A

mono

21
Q

SI of activity

A

Bq

22
Q

SI of Source strength

A

Kerma

23
Q

Why is HVL more useful in BRachy than EBRT?

A

Because source is mm from surrounding tissue.

24
Q

Do sources emitt radiation equally in all directions?

A

no

25
Q

does brachy incorporate tissue inhomogeneity into the

dose calculation algorithm?

A

Currently, brachytherapy treatment planning systems
do not incorporate tissue inhomogeneity into the
dose calculation algorithm

26
Q

When is ultrasound used for needle insertion

A

prostate and cervix

typically used in operating theatre.

27
Q

When is fluroscopy used in brachy?

A

needle insertion

Allows position feedback and to see metal needles and seeds but can have poor visualization in some areas.

28
Q

For CT imaging why do applicator needles need to be stainless steel?

A

to reduce CT artifacts

29
Q

Is it hard to visualise a tumour in CT? in prostate and cervix for example

A

yes

30
Q

When was point doses predominatly used?

A

cervix implantation

31
Q

Which point is used as the prescription point?

A

Point A

32
Q

Is the point A on the left or right?

A

both. one for each side.

33
Q

What is the refrence dose rate?

A

85% of basal dose rate.

34
Q

What is HR-CTV?

A

High risk clinical target volume

35
Q

When is HR-CTV most commonly used?

A

Cervix

36
Q

What dose rate is used for HR-CTV D90

A

HDR

37
Q

What is the minimum dose for HR CTV D90

A

90% of HRCTV

38
Q

What does MPD stand for?

A

Minimum/ mean periphery dose

39
Q

when is MPD used?

A

Prostate

40
Q

what is minimum PD

A

the maximum dose rate needed to cover the entire target volume

41
Q

WHat is mean PD

A

average dose at surface of target volume

42
Q

which is less varied out of minimum and mean PD

A

MEan

43
Q

What is the basal dose rate?

A

the average dose rate between each pair of needles

MRSC 2501 (3 decks)

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