Title: Medical Physics
1Part 2
2What can radiation do?
Death Cancer Skin Burns Cataract Infertility Genet
ic effects
2
3What can radiation do?
Deterministic effects death, skin burns,
cataract, infertility Stochastic
effects cancer, genetic effects
3
4Early Observations of the Effects of Ionizing
Radiation
- 1895 X Rays discovered by Roentgen
- 1896 First skin burns reported
- 1896 First use of X Rays in the treatment of
cancer - 1896 Becquerel Discovery of radioactivity
- 1897 First cases of skin damage reported
- 1902 First report of X Ray induced cancer
- 1911 First report of leukaemia in humans and
lung cancer from occupational exposure - 1911 94 cases of tumour reported in Germany
(50 being radiologists)
5OBJECTIVES OF RADIATION PROTECTION
- PREVENTION of deterministic effect.
- LIMITING the probability of stochastic effect
5
6Radiosensitivity RS
- RS Probability of a cell, tissue or organ of
suffering an effect per unit of dose.
7RADIOSENSITIVITY
High RS Medium RS Low RS
Gonads Thyroid Eye lens Bone Marrow Spleen Lymphatic nodes Lymphocytes Skin Mesoderm organs (liver, heart, lungs) Muscle Bones Nervous system
8Why do we need protection?
- It is generally assumed that even very small
doses of ionizing radiation can potentially be
harmful . - Therefore, persons must be protected from
ionizing radiation at all dose levels.
8
9Who should be protected in Hospital?
- Patients.
- Members of his/her family.
- Workers.
- General public.
9
10Ionizing Radiation
We live with 1-3 mSv/y
Can kill 4000 mSv
10
11Patients Protection
- Persons are medically exposed as part of their
diagnostic or treatment - According to IAEA, ICRP and BSS, two basic
principles of radiation protection are to be
complied with - justification and optimization
12RP Principles vs. Actions
- Justification
- Optimization
- Dose Limitations
- Time
- (dose directly proportional to length of
exposure). - Shielding
- (b/w source and patient).
- Distance
- (Intensity and StP distance).
13Justification
- No use of ionizing radiation is justified if
there is no benefit. - All applications must be justified.
- This implies All, even the smallest exposures
are potentially harmful and the risk must be
offset by a benefit.
13
14The justification of a practice
- The decision to adopt or continue any human
activity involves a review of benefits and
disadvantages of the possible options - E.g. choosing between the use of X Rays or
ultrasound - Most of the assessments needed for the
justification of a practice are made on the basis
of experience, professional judgement, and common
sense.
15Risk/Benefit analysis
- Need to evaluate the benefits of radiation - an
easy task in the case of nuclear medicine. - Radiation is the diagnostic and therapeutic
agent. - Assessment of the risks requires the knowledge of
the dose received by persons.
15
16Optimization
- When radiation is to be used then the exposure
should be optimized to minimize any possibility
of detriment. - Optimization is doing the best you can under the
prevailing conditions. - Need to be familiar with techniques and options
to optimize the application of ionizing radiation
- this is really the main objective of the
present course.
16
17Optimization
- Reducing the patient dose may reduce the quantity
as well as the quality of the information
provided by the examination or may require
important extra resources. - Means that doses should be As Low As Reasonably
Achievable ALARA, economic and social factors
being taken into account compatible with
achieving the required objective.
18Optimization principle ALARA
18
19OPTIMIZATION OFPATIENT EXAMINATION
Diagnostic objective Medical exposure
20Optimization of image quality
- Image quality depends on
- Administered activity
- Technical factors - equipment used -
acquisition protocol - image processing
evaluation - noise - spatial resolution - - scatter
- Patient factors - size
- - age
- - disease - movement
21Framework of RP for medical exposure
- Justification
- Optimization
- The use of doses limits is NOT APPLICABLE
- Dose constraints and guidance (or reference)
levels ARE RECOMMENDED
22Three types of exposure
- Medical Exposure (principally the exposure of
persons as part of their diagnostic or treatment) - Occupational Exposure (exposure incurred at work,
and practically as a result of work) - Public Exposure (including all other exposures)
23Medical exposure
- Medical Exposure
- Exposure of persons as part of their diagnostic
or treatment. - Exposures incurred by volunteers as part of a
program of biomedical research.
24Responsibilities for Medical Exposure
- (a) No patient to be administered a diagnostic
or therapeutic medical exposure unless the
exposure is prescribed by a medical
practitioner - (d) For therapeutic uses of radiation, the
calibration, dosimetry and quality assurance
requirements of the Standards be conducted by or
under the supervision of a qualified expert in
radiotherapy physics.
24
25PUBLIC
- effective dose of 1 mSv/year
- equivalent dose to lens of the eye 15 mSv/yr
- equivalent dose to skin of 50 mSv/year.
26Guidance levels for diagnostic radiography
(typical adult patient)
Examination Entrance surface dose per radiograph (mGy)
Lumbar spine AP 10
Lumbar spine LAT 30
Lumbar spine LSJ 40
Abdomen, IVU and cholecystography AP 10
27Guidance levels for diagnostic radiography
(typical adult patient)
Examination Entrance surface dose per radiograph (mGy)
Pelvis AP 10
Hip joint AP 10
Chest PA 0.4
Chest LAT 1.5
28Typical effective doses from diagnostic medical
exposures
Diagnostic procedure Typical effective dose (mSv) Equiv. no. of chest x-rays Approx. equiv. period of natural background radiation
Chest (single PA film) 0.02 1 3 days
Skull 0.07 3.5 11 days
Thoracic spine 0.7 35 4 months
Lumbar spine 1.3 65 7 months
From Referral Criteria For Imaging. CE, 2000.
29Typical effective doses from diagnostic medical
exposures
Diagnostic procedure Typical effective dose (mSv) Equiv. no. of chest x-rays Approx. equiv. period of natural background radiation
CT head 2.3 115 1 year
CT chest 8 400 3.6 years
CT Abdomen or pelvis 10 500 4.5 years
From Referral Criteria For Imaging. CE, 2000.
30OCCUPATIONAL - APPENDIX I
- Dose Limits
- effective dose of 5mSv per year averaged over
five consecutive years - equivalent dose to lens of eye of 150mSv in a
year - equivalent dose to extremities or skin of 500mSv
in a year. - For apprentices (16-18 years of age)
- effective dose of 6mSv in a year
30
31OCCUPATIONAL
- Female workers should notify pregnancy.
- Working conditions shall be adapted to ensure
that the embryo and fetus are afforded the same
broad level of protection as for members of the
public.
31
32Class Activity 3
- Mr. Sharp, I am given to understand that 2 bone
scans and a cardiac study done on me have given
me 22 mSv whereas 20 mSv is the safe dose. I want
to file legal suit against the doctor. What do
you feel??