dose limits
- to whole body
- to organs
- lens of eyes
- 5 mrem/yr
- 50 mrem/yr
- 15 rem/yr
dose limits
- public (waiting room)
- minor workers (<18)
- declared pregnant woman
- 100 mrem/yr
- 10% of worker limits
- 500 mrem/term (recommended <50 mrem/month)
typical dose currently received from a chest xray
8 mrem
recommendations for pregnant workers
- greater risk in first trimester
- in first 2 weeks either no harm or total loss
- weeks 2-12: congenital abnormalities and mental retardation
- after 41 days there is a risk of cancer
how many rem for pregnant workers
0.5 rem
properties of a radionuclide that would make it good for diagnostic studies
- Use a small amount (short half-life)
- Carrier must be soluble but stable
- Radionuclide that can be combined with many carriers
- Should ideally emit only gammas
- Gamma energy should be high enough to escape the body and low enough to be readily detectable (50 keV to 200 keV)
- Effective half-life of radionuclide should be long enough for good imaging but not too long
effective half life equation
effective half life = physical half-life + biological half life
Tc-99m
- half-life
- energy
- metastable?
- type of chem
- 6 hours
- 140 keV
- yes
- good
I-123
- used for what
- energy
- type of energy
- half-life
- type of chem
- thyroid
- 159 keV
- gamma
- 15 hrs
- limited
I-131
- used for what
- energy
- what energy is too high
- half life
- therapy
- 364 keV
- gamma
- 8 days
CT
- adv.
- disadv.
- excellent contrast resolution
- good image of structure
- gives cross-sectional image
- excellent contrast resolution
- expensive compared to xray
- high dose to local area (800 mrem)
- heavy duty xray tube
- expensive compared to xray
PET
- type of energy
- collimator?
- resolution
- 3 problems
- specific
- no
- 2-5 mm
- expensive
- hard to produce nuclear med
- accelerator
- expensive
external beam
method for delivering high-energy x-ray beams to a patient’s tumor
brachytherapy
sealed radiation source is placed inside or next to the area requiring treatment
monoclonal antibodies
an antibody produced by a single clone of cells
-enlist natural immune system functions to fight cancer
gamma knife
focuses low-dose gamma radiation from many sources on a precise target
properties of a good radionuclide for therapy and how it differs from those used in diagnostic
- Intentional high dose to tumor (fatal)
- Side effects due to radiation acceptance (within limits)
- Significant risks to patient and to you
- Long course of treatment
- Internally (Want short range emitters (alpha and beta))
- Externally (Want high energy gammas and x-rays)
