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Skin Radiation therapy > Bratty therapy (in general) > Flashcards

Bratty therapy (in general) Flashcards

1
Q

requirements for 1/2 life of permanent vs temporary implants

A

few days or more for permanent implants

few weeks for temporary implants

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2
Q

what is the general energy for bratty sources

A

typically between .35-.66MEV

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3
Q

Production of Ir-192 for bratty (equation)

A

191 IR+ n =192 Ir +gamma

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4
Q

production of Ra-226 for brachy equation

A

Ra226 =Rn222+ He 4(alpha) + gamma

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5
Q

production of Cs-137 brachy equation

A

137 Cs= 137Ba+ 0 electron +gamma

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6
Q

production of cobalt 60 brachy equation

A

60Co= Ni 60+ 0 e +gamma

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7
Q

Ra-226 usual form, production, 1/2 life, emmisions

A

tubes, needles
naturally occurring
1620 y
2.45 Mev gamma

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8
Q

Cs-137 usual form, production, 1/2 life, emissions

A

tubes, needles, after loading
fission product
30.17 y
.662 Mev gamma

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9
Q

co-60 usual form, production, 1/2 life, emissions

A

tubes, after loading
neutron activation
5.26y
1.17, 1.33 Mev gamma

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10
Q

Ir-192, usual form, production, 1/2 life, emissions

A

wires, after loading
neutron activation
74d
.38Mev gamma

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11
Q

i-125 usual form, production, 1/2 life, emmisions

A

seeds
daughter of xenon-125
59.6 d
27.4,31.4,35.5Kev X-rays

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12
Q

pd-103, usual form, production, 1/2 life, emissions

A

seeds
neutron activation
17d
21 kev xray

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13
Q

au-198 usual form, production, 1/2 life, emissions

A

grains,
neutron activation,
2.7d, .
412 Mev gamma

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14
Q

Sr-90 usual form, production, 1/2 life, emissions

A

plaques
fission product
28.7 y
2.27 Mev beta particles

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15
Q

Ru-106 usual form, production, 1/2 life, emissions

A

plaques
fission product
1.02 y
3.54 Mev beta particles

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16
Q

gold decay equation

A

198 Au = 198 Hg +0 electron + gamma

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17
Q

strontium decay equation

A

90 Sr= 90Y+0electron

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18
Q

ruthenium 106 decay equation

A

106 Ru=106 Rh +0electron

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19
Q

definition of intracavitiary brachy

A

insertion of bratty sources into a preexisting body cavity (ex: uterine canal or vagina)

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20
Q

definition of interstitial brachytherapy

A

insertion of source directly into the tissue (ex: wire implant to the breast floor of mouth etc.)

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21
Q

definition intraluminal brachytherapy

A

insertion of brachy sources into a lumen (bronchus or esophagus)

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22
Q

intravascular brachytherapy definition

A

insertion into artery

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23
Q

dose rates for LDR brachy

A

.5Gy/hr -1Gy/hr

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24
Q

dose rates for MDR brachy

A

1Gy/hr-12Gy/hr

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25
Q

dise rate for HDR brachy

A

> 12Gy/hr most HDR machines operate at 2gy//min

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26
Q

what is PDR

A

pulse dose rate, occurs when HDR pulses of treatment (lasting 5-10 mins) are repeated at short intervals to simulate radiobio effects of LDR while using HDR machine

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27
Q

manual after loading is done for what type of brachy only

A

LDR

28
Q

Matching after loading is used for what types of brachy

A

LDR, HDR

29
Q

examples of manual applications

A

Ra-226 or Cs-137 needles used for Gyne cancer
I-125 or Pd-103 is an example of seeds that are manually inserted for prostate and are a permanent implant
beta emitting eye plaques Sr-90 and Rn-106 are also applied manually

30
Q

planar implant distribution rules

A

aka paterson parker rules
area of implant peripheral fraction area fraction
<25cm 2/3 1/3
25-100cm 1/2 1/2
>100cm 1/3 2/3

31
Q

distribution rule for volume implants

A

implanted volume is divided into rind and core
shape middle part of rind core each end
cylinder 4parts 2 parts 1 part
sphere 6prts 2 parts
cuboid 1 part (each side) 2 parts 1 part

32
Q

what is the paris system used for?

A

determined dose distributions around Ir-192 wire implants gives LDR treatments .5Gy/hr

33
Q

Manchester system sources should be _____.vs paris system sources should be ______.

A

interstitial sources should be crossed at the end of the implant in the manchester system
paris system the sources should be straight and paralell

34
Q

3 geometrical arrangements for the paris system, which arrangement is used for which cancer

A
  • single plane that can be slightly curved (chest wall or anal margin)
  • multiple plane arrangement can be in a triangle for thicker tumours ex: treating breast implants or tumours of the lip or cheek
  • multiple plane arrangement can also be in a square to treat tumours of the tongue
35
Q

central plane as defined by the paris system

A

the central plane is where we calculate from.

In the paris system this is defined as a plane perpendicular to the sources midway along the sources

36
Q

whats basal dose points

A

the area of minimum dose rate between the wires

37
Q

where are the basal dose points located in single plane, triangular plane arrangement and square plane arangement

A

min dose is midway between each wires
triangle- centre of gravity (centroid) of the triangle
square - at the centre of each square

38
Q

what is the reference dose rte in terms of the basal dose rate

A

reference dose rate is 85% of the basal dose

39
Q

SI unit of exposure

A

c/kg (coulomb per kilogram ) it is denoted by X

the original unit was in Rottens and = 2.58x10-4 c/Kg

40
Q

SI unit of absorbed dose

A

Gy and it is denoted by D

the original unit was rads where 1Gy=100 rads

41
Q

SI unit for equivalent dose

A

Sv (sieverts) equivalent dose is denoted by H

42
Q

what is a stochastic effect

A

when a cell that us damaged by XRT and is imperfectly repaired
this can be further divided into somatic and genetic effects
Somatic effects- affect the individual who was radiated
genetic effects- affect subsequent generations as a result of XRT reproductive organs

43
Q

dose limits/ year for XRT workers vs the general public

A

area dose XRT worker dose public
whole body 50mSv 1mSv
lens of the eye 150mSV 15Msv
dose to skin 500mSV 50mSV
Hands forearm, feet 500mSV 50Msv

44
Q

how is brachytherapy source strength measured

A

re-entrant ionization chamber

45
Q

how close should the measured source strength be to the calibration certificate f source strength

A

measured source strength should be +/- 5% OF THE CALIBRATION CERTIFICate source strength

46
Q

leakage tests in brachytherapy

A

tested annually or when damage is expected the process includes wiping off the source using forceps with a swab with water or methanol the swab is measured using a NA-i SCINTILLATION COUNTER

47
Q

what level is considered a leakage in brachytherapy

A

a leak is considered to occur when the levels from the swab is >200Bq if <200Bq it is considered leak free

48
Q

what tools should be used when handling radioactive sources

A

use long forceps to avoid touching the source with your fingers
when transporting the source should be in a protective container

49
Q

what type of bratty can be performed in a ward room ? what type needs a specially designed room

A

remote after loading has its own room and the source stays in the room nd the room is not used for any other purpose
prostate seeds can be implanted in any ward room (Pd103, I-125, Ir-192 wire)

50
Q

the 3 methods of calibrating brachy sources

A

1.re-entrant ionization chamber is the most common method used for LDR sources for manually after loading
2.thimble ionization chamber measures AKR (air karma rate) directly used for measuring HDR sources
3,thimble ionization chamber in a solid phantom

51
Q

how often is the 1r-192 source replaced

A

every 3 months

52
Q

pretreatment checks for HDR afterloding

A 
machine function tests 
source data checks 
positional accuracy 
timing accuracyl accuracy
applicator integrity
53
Q

tolerance of positional accuracy

A

+/- 1mm

54
Q

tolerance of timing accuracy

A

+/-1%

55
Q

quarterly checks for HDR afterloacing

A

source calibration
source position set up and verification
pre-treatment tests

56
Q

tolerance for source calibration

A

+/- 3%

57
Q

SOURCE POSITION SET-UP AND CALIBRATION TOLERANCE

A

+/- 1MM (aim for .5mm)

58
Q

re-entrant ionization chamber tolerance

A

monthly tolerance of +/- 3%

annual tolerance of +/-2%

59
Q

calculating air karma rat (AKR) with a re-entrant ionization chamber (for HDR source calibration)

A

RAKR= I new xF elec x K dec x K tp X Kion X K sg X N Kr
where: i raw= ionization current displayed on the electrometer in amps
Felec= electrometer correction factor to convert displayed current in Amps to actual current
K dec= decay corrects measured reading back to certificate reference date and time
K tp= temperature and pressure correction factor
(273,15T / 293.15 x 1013.25/ P(mbar)
Kion= ion recombination factor
Ksg= source geometry factor the corrects when hospital source is different HDR source
Nkr= callibration coefficent to convert corrected instrument to RAKR for Ir-192 unit = Gy C-1 at 1 m

60
Q

how thick do the walls need to be for HDR brachy

A

40-60cm of concrete

61
Q

dose limit to the fetus

A

total dose =5msv

dose equivalent / month =.5mSV

62
Q

What is the most significant factor influencing the shielding design for an accelorator

A

workload

63
Q

preferred HDR SOURCE

A

Ir-192

64
Q

activity for HDR

A

10Ci

65
Q

activity for PDR

A

1Ci

66
Q

doses for PDR

A

1-3Gy/hr

67
Q

LDR source

A

cesium, I-125, IR-192

Skin Radiation therapy (40 decks)

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