Physics/Radiopharm 2017 Flashcards
Stats - reproducibility, population, reliability and bayes theorem
Reproducibility - ability to get the same research results or inferences, based on the raw data and computer programs provided by researchers.
Reliability - overall consistency of a measure. A measure is said to have a high reliability if it produces similar results under consistent conditions.
A population in statistics is a set of similar items or events which is of interest for some question or experiment.
Bayes theorem: The probability of event A (e.g., having breast cancer) given event B (having a positive mammogram) depends not only on the relationship between A and B (i.e., the accuracy of mammograms) but on the absolute probability (occurrence) of A not concerning B (i.e., the incidence of breast cancer in general), and the absolute probability of B not concerning A (i.e. the probability of a positive mammogram).
The absolutely crucial point to remember from Bayes’ theorem is that the prior probability (or pretest clinical assessment) is as important as the sensitivity and specificity of the diagnostic test in the determination of the post-test probability (the probability that the patient with a positive test truly has the disease).
60 Gbq in dose calibrator why measure less, how to fix, what amino acids why use them?
May measure less because of of incorrect radionuclide setting chosen, did not set to zero, high background, battery issue, constancy issue. Fix by performing QC such as constancy, set to zero, check voltage and battery. Dose calibrator is filled with argon and traces of halogen at high pressure. Its operating voltage is about 150 V.
10 % versus 20 % mediastinoscopy what relative risk reduction in % what NNT
ARR = ARC - ART = 0.20 - 0.10 = 0.10 = 10%
RRR = (ARC-ART)/ARC = (0.20 - 0.10) / 0.20 = 50%
NNT = 1/ARR = 1/0.10 = 10
AR (absolute risk) = the number of events (good or bad) in treated or control groups, divided by the number of people in that group
ARC = the AR of events in the control group ART = the AR of events in the treatment group
ARR (absolute risk reduction) = ARC – ART
RR (relative risk) = ART / ARC
RRR (relative risk reduction) = (ARC – ART) / ARC
RRR = 1 – RR
NNT (number needed to treat) = 1 / ARR
How to produce Tc - 2 ways
Using Fission MOLY in generator
99Mo → 99mTc + β− + νe
Cyclotron produced
100Mo(p,2n)99mTc
Describe coincidence events and whether accepted (RC)
True, scatter, random.
True and Scatter events increase linearly with activity; random events increase with the square of activity.
To decrease random events: use 2D imaging with septa, reduce dose, scatter correction (delayed window method or singles method), reduce coincidence acceptance window.
High count rate what happens to lost counts, what about NaI crystal?
High count rate leads to Dead time, which refers to the time required to process individual detected events. Dead time is the period of time that a counter remains insensitive to count the next event after an event. Dead time reduces sensitivity, which reduces S/N ratio. Images are noisier due to dead time, but the spatial resolution is unchanged. Events that occur in the dead time are lost, and in paralyzable systems, extend the dead time even further.
A counting system can be classified as being paralyzable or non-paralyzable.
A non-paralyzable system is one for which, if an event occurs during the dead time of a proceeding event, then the second event is simply ignored with no effect on subsequently occurring events. Observed counting rate: RO = Rt/(1 + Rt τ)
A paralyzable system is one for which each event introduces a dead time, whether or not that event was actually counted. Therefore, an event occurring during the dead time of a proceeding event would not be counted but still would introduce its own dead time during which subsequent events could not be recorded. Most radiation detectors behave as paralyzable systems. RO =Rt e-Rt τ , ROmax = 1/(eτ)
Radioprotectors and dose rate factor
Most radioprotectors are sulfhydryl compounds. They contain a sulfhydrl group (S-H) attached to a short carbon chain with a reactive compound at the opposite end. The example from Hall et all is cysteamine:
SH−CH2−CH2−NH2
These agents are only effective on radiation types that require oxygen for ‘fixing’ - ie. that function through indirect action of radiation
Cytoprotective mechanisms of sulfylhydryl compounds:
1. Free radical scavenger
The sulfhydryl group may act by chemically reacting with free radicals generated by indirectly ionising radiation and preventing their interaction with DNA
2. Proton/hydrogen donor to aid in chemical repair of DNA damage
The sulhydryl group may donate a hydrogen atom to assist in DNA repair pathways.
Define RBE, 2 factors that effect this (RC
Relative biologic effectiveness (RBE) of some test radiation (r) is the ratio D250/Dr, in which D250 and Dr are the doses of 250-kV x-rays and the test radiation, respectively, required to produce equal biologic effect. RBE = D250 / Dt = (Dose of 250 kVp X-rays) / (Dose of test radiation) to cause equivalent effect
RBE increases with LET to a maximum at about 100 keV/μm, thereafter decreasing with higher LET. For radiation with the optimal LET of 100 keV/μm, the average separation between ionizing events is similar to the diameter of the DNA double helix (2 nm). It can most efficiently produce double-strand breaks by a single track.
RBE depends on the following: o Radiation quality (LET) o Radiation dose o Number of dose fractions o Dose rate o Biologic system or end point
Anatomy of central neck (RC)
Hyoid bone (superior)
Carotid arteries (laterally)
Superficial layer of deep cervical fascia (anteriorly)
Deep layer of deep cervical fascia (posteriorly)
Innominate artery on right and corresponding axial plane on left (inferior)
Rb-82 how it is taken up, % myocardial retention at rest and stress in an animal model (?rabbit) and two things that increase this retention
Rb-82 is a potassium analog and is taken up by myocardial cells via the Na+/K+ ATP transporter in a rapid and active manner. Myocardial extraction fraction 65%.
What 3 radiopharmaceuticals stop breastfeeding (kinda RC)
I-123 (NaI), I-131 (NaI), Ga-67 citrate
3 Causes of radiopharmaceutical breakdown (RC)
o Changes in temperature or pH
o Light
o Presence of oxidizing or reducing agents
o Radiolysis
o Decomposition of the radiopharmaceutical due to the action of a solvent
8 things for major spill (RC)
Notify all persons in area and clear the area
Leave fume hood running
Close off and secure spill area
Remove contaminated clothing and clean skin
Notify RSO
Clean spill working from outside in with protection
Put all contaminated stuff in radioactive waste
Wipe test for residual contamination as appropriate
Arrange bioassay if necessary
Submit written report
5 things to change spect to pet
More shielding for room
Source of radiopharmaceuticals from supplier
Consider purchasing cyclotron
Attenuation correction for PET/MR or PET/CT
Train technologists who are inexperienced in CT
2 pet generator produced radionuclides with parent named (RC)
82Sr/82Rb
25.4d/76s
o 68Ge/68Ga
271d/68m
Stochastic vs deterministic (cancer, cataracts, sterility) (RCish)
Deterministic effect: radiobiologic effect with a threshold dose; severity ↑ with radiation dose
Example: cataract, sterility, and skin erythema
Stochastic effect: radiobiologic effect where probability of occurrence ↑ with radiation dose, but severity independent of dose; no threshold dose
Example: cancer and heritable mutations
Linear No Threshold: define- 2 things that happen indicating this is wrong (RC)
Linear No Threshold Model assumes that the long term biological damage caused by ionizing radiation is directly proportional to the dose. All radiation is considered harmful with no safety threshold, and the sum of several small exposures are considered to have the same effect as one larger exposure.
Among humans, there is no evidence of a carcinogenic effect for acute irradiation at doses less than 100 mSv and for protracted irradiation at doses less than 500 mSv
Atomic bomb data do not provide solid arguments for the LNT model. dose response is not linear at doses less than 150 mSv. In fact, a quasi-threshold, or even a hormetic effect, may exist below this dose.
Hormesis: Upregulation of protective mechanisms at the cell and tissue levels by low doses likely also operates against carcinogenic factors other than ionizing radiation and against spontaneous cancer, as demonstrated in various experiments in vitro and in vivo. Indeed, a dose of 10 mGy reduces the rate of spontaneous transformation in culture cells below the background level.
Electron capture, what else comes out, another electron capture isotope and does this cause transmutation (RC
Electron capture: p+ + e- → n + νe + Q
Neutrino carries away some of the energy, and when the orbital vacancy is filled, either characteristic x-ray or Auger electron is emitted. ↑Z favours EC. Larger elements favour EC as the K-shell is closer to the nucleus and more easily captured.
Some EC radiopharmaceuticals: Tl-201, Ga-67, I-123, I-125, In-111, Xe-127. Se-75
Yes, transmutations.
Cell phases in order of sensitivity
Cells in S-phase are typically radioresistant, those in late G2 and M phase are relatively sensitive.
From least radiosensitive to most radiosensative:
S; G1; early G2; late G2; M
Backprojection what is issue, how to fix, what is method used
Simple backprojection has inherent 1/r blurring. Fix it by using Filtered Backprojection. Ramp filter selectively amplifies high-frequency components relative to low-frequency components. The filter removes the 1/r blurring and star artifact present in simple backprojection and sharpens image detail, but it also amplifies high-frequency noise components in the image.
Transport index define and maximum dose for 3 package types (RC)
Transport Index (TI) = dose rate measurement at 1 meter in uSv/hr divided by 10
White I - maximum TI <0.05
Yellow II - 1.0
Yellow III - 10
Components of DTPA kit and relative proportions and why?
Main components: DTPA and stannous chloride
10^5-10^8 mol DTPA : 10^3-10^6 mol Sn2+ : 1 mol 99mTc
o Need enough Sn2+ to reduce all 99mTc
o Need greater amount of chelate to drive chemical equilibrium to form chelated complexes, and prevent Sn and Tc colloid formation
o pentasodium or calcium trisodium salt of DTPA – chelating agent
o stannous chloride dihydrate in lyophilized from - reducing agent of Tc-99mO4-
o ascorbic acid – stabilizer
Tin:
Too much: Hydrolysis of tin increases, may precipitate some of the reduced Tc-99m to form Tc-99m-Sn-colloid and other Sn-complexes, reducing yield of the labeled chelate
Too little: Incomplete reduction of Tc-99m to desired oxidation state and lower yield, and results in an increase in free pertechnetate.
Pertechnetate:
Too high a concentration with O2 can lead to radiolysis and the production of free radicals, which will interact with the chelates to form free pertechnetate. However kit limits are well below this.
The pH is adjusted to 3.9-4.1 with sodium hydroxide and/or hydrochloric acid prior to lyophilization. No bacteriostatic preservative is present
Effective dose for NEW and public
A NEW is any person who in the routine performance of their profession, business or employment will expect to be exposed to more than the prescribed limit of ionizing radiation for the general public (>1 mSv)
b) What is dose limit for NEW?
100 mSv over 5 years with a maximum of 50 mSv in any one year
c) What is dose limit for public?
1 mSv per year
The dose limit for pregnant workers is 4 mSv from the time the pregnancy is declared to the end of the term.
P32 route, 1/2 life and decay
P32 sodium orthophosphate Dose/route: 6-12 mCi IV Half-life: 14.3 days Decay: Pure beta emitter βmax: 1.71MeV Range: 8 mm ST, 3mm bone
Relative front
Relative front (Rf) is the ratio of the distance traveled by given compound within a solution during paper chromatography or ITLC, to the distance traveled by the solvent.
1/2 lives I-125, I-131, I-123, Ga-67, Ga-68, Y-90, Tl-201, In-111, Sr-89, Mo-99, ?Tc-99m (RC)
I-125 (59 days), I-131 (8 days), I-123 (13.2 hours), Ga-67 (78 hours), Ga-68 (68 minutes), Y-90 (64 hours), Tl-201 (73 hours), In-111 (67 hrs), Sr-89 (50.5 days), Mo-99 (66 hours), Tc-99m (6 hours)
Quenching gas, where is it and what does it have to do? (RC)
Ionized quenching gas that can recombine with electrons without giving off UV radiation (by dissociating into molecular fragments)
Absorb UV radiation inhibiting further ionization.
Electron donor
Quenching gas is used in a Geiger Mueller counter to prevent additional avalanche ionization from
positive ion cloud. They are commonly made from
o heavy organic vapors (alcohol) - more effective but can be used up because molecular fragments do not recombine after dissociation
o halogen gases (Cl2) – recombine after dissociation so essentially unlimited lifetime in GM counter
gives up electrons easily to neutralize positive ions, converting ion cloud into ionized molecules of quenching gas
when ionized quenching gas molecules are neutralized by electrons, they de-energize themselves by dissociating into molecular fragments instead of emitting UV photons
strong absorbers of UV radiation
Weighting factors for photon, electron, alpha and 1st 1/2 of neutrons
Equivalent dose = absorbed dose x Wr (radiation weighting factor)
Wr = 1 for x-ray, gamma ray, electrons, positrons
Wr = 2 OR 5 for proton (Sorenson P406)
Wr = 20 for alpha, fission and heavy nuclei
Wr = 5-20 depending on neutron energy
CT photon effects and which one dominates > 100 keV
Photoelectric effect at < 100 keV
Compton scatter begins to dominate > 100 keV
Pair production at > 10 MeV
Ra 223, 1/2 life, what is eventual stable daughter, how much energy and how many alphas?
Ra-223: t½ of 11.4 days, eventual stable daughter: Lead-207 (Pb-207), after six-stage decay. Energy range: 5-7.5 MeV # of particles: 4 alpha particles
