S2805(a)
Semester 2, 2010
Page 1 of 11
THE UNIVERSITY OF SYDNEY
MRTY 1036 – HEALTH PHYSCS
AND RADIATION BIOOGY
NOVEMBER 2010
Time allowed: TWO HOURS
Total marks: 80 MARKS
INSTRUCTIONS
•
•
•
All questions are to be answered.
Use the answer sheet provided for section A and the answer book for section B.
Hand in the answers to section A and B separately at the end of the examination.
DATA
Free fall acceleration at earth's surface
Speed of sound in dry air (0°C)
Speed of light in vacuum
Permittivity of free space
Permeability of free space
Elementary charge
Electron volt
Speed of light in vacuum
Planck’s constant
Boltzmann constant
Atomic mass unit
Rest masses - electron
- proton
- neutron
- hydrogen atom
Conversion of curies to becquerels
Conversion of roentgens to coulombs per kg
-2
g = 9.8 m.s
-1
v = 331 m.s
8
-1
c = 2.998 × 10 m.s
-12 2 -1 -2
ε0 = 8.854 × 10 C .N .m
-7
-1
µ0 = 4π × 10 T.m.A
-19
e = 1.602 × 10 C
-19
1 eV = 1.602 × 10 J
8
-1
c = 2.998 × 10 m.s
-34
h = 6.626 × 10 J.s
-23
-1
k = 1.381 × 10 J.K
-27
u = 1.66054 × 10 kg
-31
kg
-27
kg
-27
kg
me = 9.10938 × 10
mp = 1.67262 × 10
mn = 1.67493 × 10
-27
mH = 1.67353 × 10 kg
10
1 Ci = 3.700 × 10 Bq
-4
1 R = 2.58 × 10 C.kg-1
S2805(a)
Semester 2, 2010
Page 2 of 11
Formula Sheet
A = A0 e− λt
N = N 0 e− λt
E = ∑ H T WT
ln 2
λ
T1/2 =
T
log N = log N 0 − 0.4343 λ t
Y + β− + ν
1
λ
A
−
ZX +β →
Y + β+ + ν
A
Z
A
Z
X→
A
Z +1
A
Z
X→
A
Z −1
∑N
N=
R=
n
N
t
VR =
σR
× 100%
R
1
T1 2 ( eff )
1
T1 2 ( phys )
Y +α
A− 4
Z −2
σN =
N
n
σR =
R
t
⎡ ( Rs + 2Rb ) ⎤ ⎛ 100% ⎞ 2
t=⎢
⎥ ⎜⎝
⎟
Rs2
⎣
⎦ V ⎠
R
+ b
tg
tb
=
X→
Y +ν
A
Z −1
Rs = Rg − Rb
Rg
σ Rb =
Tav =
+
1
T1 2 (bio)
ρ=
m
V
D = Eabs m
dose rate = D ΔT
H = DQ = DWR
H eff = H T WT
•
H [ µSv/h ] =
•
H=
0.14A [ MBq ] E [ MeV]
d 2 [m]
•
H [ µSv/h ] =
where Eav = Emax 3
ΓA
d2
A = 1.44 A0T1 2
D1r12 = D2 r22
D10 = ln (10 ) × D0
v = fλ
⎛ I⎞
β = (10dB ) log ⎜ ⎟
⎝ I0 ⎠
sin θ a nb
=
sin θ b na
I r [ Z 2 − Z1 ]
=
I 0 [ Z 2 + Z1 ]2
2
Z = ρv
5A [ MBq ] Eav [ MeV]
,
d 2 [m]
⎛ v + vL ⎞
fL = ⎜
fS
⎝ v + vS ⎟⎠
S2805(a)
Semester 2, 2010
Page 3 of 11
Section A
Please use the answer sheet provided for this section.
20 multiple choice questions (1 mark each)
Question 1
The diagram below is a portion of a plot where each nuclide is plotted using their Z
and N numbers.
Which position would a nucleus occupy if it needs to undergo β+ decay in order to
become stable?
(a) 1
(b) 2
(c) 3
(d) 4
Question 2
Which of the following graphs best represents the decay of a 12 MBq sample of
having a decay constant of 0.086 day-1?
(a)
(b)
(c)
(d)
A
B
C
D
131
I,
S2805(a)
Semester 2, 2010
Page 4 of 11
Question 3
The diagram below shows the head of a gamma camera.
Which of the labels on the diagram marks the scintillation crystal?
(a) A
(b) B
(c) C
(d) D
Question 4
A set of activity measurements is inaccurate and has a low standard deviation. What is
the most likely source of this problem?
(a) Systematic error
(b) Random error
(c) Periodic error
(d) The activity is changing
Question 5
The force that holds a nucleus together is called the strong nuclear force. Which of the
following statements is false?
(a) The nuclear force is stronger for larger nuclei.
(b) The nuclear force acts between any two nucleons.
(c) Without a nuclear force the nucleus would break up due to electrostatic
repulsion.
(d) The nuclear force acts over a short range.
S2805(a)
Semester 2, 2010
Page 5 of 11
Question 6
What type of radiation is emitted when a Lutetium-179 nucleus transmutes to a
Hafnium-179 daughter nucleus according to the following reaction?
179
71
(a)
(b)
(c)
(d)
Lu → 179
72 Hf + .........
α particle
β– particle
β+ particle
γ-ray
Question 7
Two different radiopharmaceuticals with identical physical half lives have been
injected into patients. Which of the following statements about them is most correct?
(a) The radiopharmaceutical with the larger biological half-life will have the
larger effective half-life.
(b) The radiopharmaceutical with the larger biological half-life will have the
smaller effective half-life.
(c) The two radiopharmaceuticals will probably have very nearly the same
biological half-life.
(d) The radiopharmaceutical with the larger effective half-life will have the
smaller biological half-life.
Question 8
In order to use a calibrated free air chamber to measure dose accurately, the condition
of ‘electronic equilibrium’ must be met. What does this mean?
(a) The pressure inside the chamber must equal the pressure outside the chamber.
(b) The flow of ionisation electrons entering the chamber from outside must
equal the flow of ionisation electrons leaving the chamber.
(c) The current of electrons flowing into the wire connected to the negative plate
must equal the current of electrons flowing out of the wire connected to the
positive plate.
(d) The number of positive charges produced by ionisation must equal the
number of negative charges produced by ionisation.
Question 9
Alpha particles have a ‘radiation quality factor’ of Q = 20. What does this mean?
(a) The risk of developing cancer due to a dose x of alpha particles to a particular
organ, is equivalent to a whole body dose of 20x.
(b) For the same dose, alpha particles carry 20 times as much energy as X-ray or
gamma ray photons.
(c) Alpha particles penetrate tissue 20 times more deeply than X-ray or gamma
ray photons.
(d) For the same dose, alpha particles do 20 times as much biological damage as
X-ray or gamma ray photons.
S2805(a)
Semester 2, 2010
Page 6 of 11
Question 10
The largest contribution to the background radiation exposure of the general
population is due to:
(a) Cosmic radiation
(b) Radon gas in the air
(c) Internal radiation from our food and drink
(d) Building materials (bricks, concrete, granite)
Question 11
Australian government regulations for stochastic effects of occupational radiation
exposure limit the individual annual whole body equivalent dose to:
(a) 1 mSv
(b) 5 mSv
(c) 20 mSv
(d) 50 mSv
Question 12
A proportional counter, being used as a dose rate meter, gives a reading of 50 µSv/hr
at a given location. When covered by 2 mm of aluminium the meter reads 10 µSv/hr
at the same location. The radiation field at this point probably consists mostly of:
(a) alpha particles
(b) beta particles
(c) gamma rays
(d) neutrons
Question 13
In the ARPANSA Safety Guide for Radiation Protection in Diagnostic and
Interventional Radiology there is statement that for the protection of the patient the
practitioner is encouraged to use DRLs as a tool to support optimisation of protection
to the patient. DRL is an acronym for which of the following terms?
(a) Diagnostic Reference Level
(b) Digital Radiation Level
(c) Diagnostic Reference Load
(d) Digital Radiation Load
S2805(a)
Semester 2, 2010
Page 7 of 11
Question 14
The ARPANSA Code of Practice for Radiation Protection in the Medical Applications
of Ionizing Radiation (2008) requires that an employee who is likely to receive an
annual effective dose of 1 mSv must be issued with a Personal Radiation Monitoring
Device. If the employee is wearing only one monitoring device, which if the
following statements incorrectly describes where this device should be worn?
(a) on the trunk
(b) between the waist and chest
(c) under any protective garments
(d) outside any protective garments
Question 15
Consider the indirect action of x-rays on biological tissue. Which of the following
options are stated in the correct chronological order – i.e. starting with the initial
interaction and ending with the biological effect?
(a) Free radical formation – Incident x-ray photon – Fast electron – Chemical
changes from the breakage of bonds – Incident x-ray photon – Biological
effect
(b) Fast electron – Free radical formation – Chemical changes from the breakage
of bonds – Incident x-ray photon – Biological effect
(c) Incident x-ray photon – Fast electron – Free radical formation – Chemical
changes from the breakage of bonds – Biological effect
(d) Chemical changes from the breakage of bonds – Incident x-ray photon – Fast
electron – Free radical formation – Biological effect
Question 16
The list below (I to VIII) represents some concepts of radiobiology:
I.
Reoxygenation
II.
Remediation
III.
Radiotherapy
IV.
Repair of sub-lethal damage
V.
Radiogenic
VI.
Reassortment of cells within the cell cycle
VII. Repopulation
VIII. Radiological exposure and dose
Which of the following sets of ‘four Rs of radiobiology’ represents the key principles
underpinning our current understanding of the subject?
(a) II, IV,VII, VIII
(b) IV, V, VI, VII
(c) I, II, III, V
(d) I, IV, VI, VII
S2805(a)
Semester 2, 2010
Page 8 of 11
Question 17
According ICRP 103, which of the following groups represents all organs with the
highest weighting factor for biological risk?
(a) Bone surface, Colon, Lung
(b) Stomach, Lung, Breast
(c) Gonads, Liver Thyroid
(d) Breast, Brain, Salivary glands, Skin
Question 18
In ultrasound imaging of the boundary between two tissue types, what would be the
effect of increasing the difference in acoustic impedance between the two tissues?
(a) No effect
(b) Signal frequency would increase
(c) Reflected signal amplitude would increase
(d) Reflected signal amplitude would decrease
Question 19
Ultrasound is generally not used to image the structure of the human lungs. Which of
the following is the primary factor preventing clear imaging of the lungs?
(a) The complex structure of the lungs
(b) Air in the lungs
(c) The bones overlying the lungs
(d) The motion of the lungs during breathing
Question 20
0 dB on the decibel scale describing the intensity of sound is defined to be equivalent
to 10-12 W.m-2. What intensity in W.m-2 corresponds to 46 dB?
(a) 1.7 × 10-12 W.m-2
(b) 46 × 10-12 W.m-2
(c) 4.0 × 10-8 W.m-2
(d) 4.0 × 104 W.m-2
This is the end of Section A.
S2805(a)
Semester 2, 2010
Page 9 of 11
Section B
Please use the booklet provided for this section.
This section has six (6) questions (10 marks each)
ANSWER ALL QUESTIONS
Question 1
(a)
Briefly describe how a planar image is formed using a gamma camera.
(b)
In no more than a few sentences, explain how each of the following helps to
reduce scatter in imaging using a gamma camera:
(i)
A collimator
(ii)
A Pulse Height Analyser
(c)
Define what is meant by ‘hot’ and ‘cold’ spots found on a nuclear medicine
image. Name one situation where each can be used to diagnose disease.
(10 marks)
Question 2
(a)
(b)
(
)
–
A sample of Xenon 133
54 Xe decays through β decay to a metastable state of
Cesium (Cs), and then the sample becomes stable.
(i)
Write out a decay equation for this process.
(ii)
What is meant by the term metastable?
(iii) Sketch a diagram of the energy spectrum of the β– particles you would
expect to observe and explain the shape of this spectrum.
(iv)
What other particles would you expect to observe? Explain what the
energy spectrum of these particles would look like and why.
Another isotope of Cs, 137Cs, has a half life of 30 years. How long does it take
for a sample of 137Cs to decay to 10% of its initial activity?
(10 marks)
S2805(a)
Semester 2, 2010
Page 10 of 11
Question 3
(a)
A patient absorbed a total of 0.30 J of energy from a beam of X-rays. The
volume of tissue affected was 1.250 × 10-3 m-3. Assuming a mean tissue
density of 103 kg.m-3, what is the absorbed dose averaged over that volume of
tissue?
(b)
Suppose the tissue in part (a) was the patient's liver, with a tissue weighting
factor of 0.05. What would be the effective full body dose that would result in
the same risk to the patient as the liver dose in (a)?
(c)
Iodine-131 has a physical half-life of 8 days. However, in an adult patient, it
has an effective half-life of 7.6 days. Calculate the biological half-life.
(d)
Suppose a radioactive isotope happens to be chemically attached to a
substance that accumulates in fat tissue so that its biological half-life is very,
very long. In this case, what effect would this have on the effective half-life of
the isotope? Does it:
1) increase to a half-life much longer than its physical half-life,
2) more closely approach the physical half-life of the isotope, or
3) decrease to a half-life much shorter than its physical half-life?
From these three, choose the correct one and explain why it is correct.
(You may use algebra in your explanation, although this is not essential).
(10 marks)
Question 4
A nurse is required to handle a particular gamma source as part of her profession.
(a)
She receives a whole body dose rate of 90 µSv.hr-1 at a distance of 1 m from
source. Calculate the distance at which she must stand from the source in order
to reduce the dose rate to 10 µSv.hr-1.
(b)
She is required to handle the source as part of radiotherapy treatment for
patients. Her personal radiation monitor shows that she receives a dose of
0.1 mSv every time she handles the source. How many times a month is she
permitted to handle the source?
(10 marks)
Question 5
(a)
A tumour containing 5 × 108 cells receives an absorbed dose of 49 Gy during
the course of radiotherapy. How many tumour cells will be left if D0 equals
approximately 3.04 Gy?
(b)
Name five factors that determine relative biological effectiveness (RBE) of
radiation.
(c)
Most adverse health effects of radiation exposure may be described as either
stochastic or deterministic. Explain the difference between these and give an
example of each.
(total - 10 marks)
S2805(a)
Semester 2, 2010
Page 11 of 11
Question 6
Some of the properties of fat and muscle tissue are given in the Table below.
Fat Density
(kg.m–3) 920 Ultrasound
velocity (m.s–1) 1450 Muscle 1040 1585 Substance (a)
Calculate the acoustic impedance of the two materials, fat and muscle.
(b)
Calculate the percentage of ultrasound energy reflected at a boundary between
fat and muscle.
(c)
Comment on the size of this reflection and the significance of this value for
ultrasound imaging.
(d)
If the interface between these two tissues is moving, how would you expect
the ultrasound reflection to be affected? Briefly explain your answer.
(10 marks)
This is the end of your questions.