Rad Bio, Protection, and Shielding
Define the use factor:
(U): Proportional amount of time during which the x-ray beam is energized or directed toward a particular primary barrier. Usually 1 but can be less if multiple primary barriers are used (wall and table bucky in rad room for example)
Types of DNA damage:
-single-stranded break in DNA backbone -double-stranded break in DNA backbone Incorrectly repaired DSB can lead to carcinogenesis. Loss of change of bases post repair = mutations Chromosomal damage before DNA replication = chromosome aberration After DNA replication = hromatid aberration
Weekly controlled shielding design goal? Uncontrolled?
0.1 mGy/wk (5 mGy/yr) 0.02 mGy/wk (1 mGy/yr)
What is the workload per patient in mA*min/patient, average and busy number of patients per week, and average and busy workload per week in a chest room?
0.22 mA*min/patient 200, 400 patients per 40hrs 50, 100 mA*min/wk
Lead apron and glasses protection factor?
0.25-0.5 mmPb equivalent apron protects >90%. 0.35-0.5 mmPb protects 95-99% but weights 50-100% more. Lead glasses protect 30-70%. Normal glasses protect 20%.
What is the workload per patient in mA*min/patient, average and busy number of patients per week, and average and busy workload per week in a chest bucky rad room?
0.6 mA*min/patient 120, 160 patients per 40hrs 75, 100 mA*min/wk
What are the limits of leakage radiation by the FDA?
0.876 mGy/hr air kerma (100 mR/hr exposure) at 1 m (FDA, 2003a).
According to 10CFR20, what are the Q factors for equivalent dose?
1 for x rays and betas 20 for alphas 10 for neutrons of unknown energy 10 for high energy protons
Dose limits to the general public?
1 mSv/yr or 0.02 mSv unless deemed necessary.
Stages of cancer development?
1. Initiation - ionizing event causes mutation that is misrepaired. 2. Promotion - On its own, does not cause cancer, but if initiated, will cause the cell to divide. 3. Progression - transformed cell eventually evades hosts defenses and develops into a tumor.
What is the workload per patient in mA*min/patient, average and busy number of patients per week, and average and busy workload per week in a floor/other rad room?
1.9 mA*min/patient 120, 160 patients per 40hrs 240, 320 mA*min/wk
What is the workload per patient in mA*min/patient, average and busy number of patients per week, and average and busy workload per week in a RF room.
13 mA*min/patient 20, 30 patients per 40hrs 260, 400 mA*min/wk
What is the workload per patient in mA*min/patient, average and busy number of patients per week, and average and busy workload per week in a cardiac angiography room?
160 mA*min/patient 20, 30 patients per 40hrs 3200, 4800 mA*min/wk
Man made radiation % of note?
18% of total risk is man made. Of the 18%: Medical imaging: 58% Nuclear medicine: 21% Consumer products: 16%
Latency period of solid tumors due to radiation?
20 years
According to NCRP 147, describe the kVp range of standard mammo installations and the requirements and recommendations of mammo rooms?
25-35 kVp Low energy may mean only gypsum wall board is needed. Shall be consulted with a qualified expert. Doors may need extra shielding since wood isn't a good attenuator.
Annual occupational dose limits?
5 rem/yr effective dose limit (to dosimeter) Effective Dose Equivalent of 50 mSv/yr to the whole body, 15 mSv lens dose, 50 rem or 0.5 Sv to any individual organ or extremity. 0.5 rem or 5mSv to the fetus of a declared pregnant worker Minors are 10% of adults. (Effective dose equivalent = D x W_R x W_t
According to NCRP 147, describe the kVp range of standard radiographic installations and the requirements and recommendations of control booths:
50-150 kVp Operator shall be able to communicate with the patient and observe them. They shall be in a protected area with a fixed shield. The exposure switch shall be positioned so the radiographer can't activate it while outside the shielded area. The booth shall be >=2.1 m high and have no unprotected line of sight from the patient or x-ray tube. The observation window shall be shielded. The control booth shouldn't be a primary barrier and should have enough room for the equipment. The window should be 45x45cm and 1.5m above the floor For dedicated chest rooms, the image receptor is the primary barrier. The wall directly around the receptor and behind it are also the primary barrier. Everything else is secondary.
Average annual effective dose (not counting therapy):
6.2 mSv, 3.1 mSv from natural sources, 3.0 mSv from medical, 1 mSv from "other". 68% of natural radiation is from radon-222. Decays from U238 and has 3.8 day half life alpha emission.
What is the workload per patient in mA*min/patient, average and busy number of patients per week, and average and busy workload per week in a mammo room?`
6.7 mA*min/patient 80, 160 patients per 40hrs 550, 1075 mA*min/wk
According to NCRP 147, describe the kVp range of standard fluoroscopic installations and the requirements and recommendations of fluoro rooms?
60-120 kVp IR rooms shall have shielding that meet shielding requirements of design goals.
What is the workload per patient in mA*min/patient, average and busy number of patients per week, and average and busy workload per week in a peripheral angiography room?`
64 mA*min/patient 20, 30 patients per 40hrs 1300, 2000 mA*min/wk
When is the the fetus most vulnerable to radiation?
8-15 weeks. Called the window of cortical sensitivity
According to NCRP 147, describe the kVp range of standard CT installations and the requirements and recommendations of CT rooms?
80-140 kVp The workload is higher but there is only secondary radiation to consider. Scatter is not isotropic.
Natural radiation risk % of note?
82% of radiation is natural background. Of the 82%: 52% is from radon gas inhalation. 20% from ingestion 16% from cosmic
What is neurovascular syndrome?
>50 Gy dose, death in 2-3 days. These doses cause massive loss of serum and electrolytes in extravascular tissues. Causes circulatory problems which is how patients die. Stages of ARS are compressed at this dose. Patients may pass out, prodromal phase within the hour, 4-6 hours of latent phase, sivere manifest illness phase with neuro changes (tremors and convulsions), then coma and death.
Occupancy factors (T):
Administrative or clerical offices; laboratories, pharmacies and other work areas fully occupied by an individual; receptionist areas, attended waiting rooms, children's indoor play areas, adjacent x-ray rooms, film reading areas, nurse's stations, x-ray control rooms 1 Rooms used for patient examinations and treatments 1/2 Corridors, patient rooms, employee lounges, staff rest rooms 1/5 Corridor doors 1/8 Public toilets, unattended vending areas, storage rooms, outdoor areas with seating, unattended waiting rooms, patient holding areas 1/20 Outdoor areas with only transient pedestrian or vehicular traffic, unattended parking lots, vehicular drop off areas (unattended), attics, stairways, unattended elevators, janitor's closets 1/40
Define air kerma:
Air kerma is the energy extracted from an x-ray beam per unit mass of air in a small irradiated air volume. Air kerma is measured in Gy.
Define the annual reference level of intake (ALI):
Annual amount of radioactive material taken in by a worker to reach the maximum allowable dose limit (50 mSv) within a year for a reference man.
Define primary and secondary barrier:
Any wall, ceiling, floor, or structure that will intercept the radiation emitted from an x-ray tube. Secondary barrier is the barrier that limits scattered secondary radiation
Methods of DNA repair:
Apoptosis: cell death if unrepairable. Short/Long patch base excision repair Nucleotide excision repair SSB repair Cross-link repair DSB repair: Homologous recombination repair or error prone Nonhomologous end-joining Base excision repair: DNA glycosylase detects damaged base and removes it Endonuclease is brought to the site where it cuts segment DNA polymerase accompanied by protein resynthesizes the DNA segment DNA ligase joins the DNA segments
What is the equation for the transmission function, defined as the ratio between the kerma before the barrier vs the kerma after:
B(x) = (P/T)d^2/(KN) K = average unshielded air kerma per patient at 1 m from the source N = # patients per week P= design dose goal T=occupancy factor (This is the same equation as the one for calculating transmission through a secondary barrier, where d is the distance to the nearest person beyond it.)
What is the equation for calculating the transmission through a primary barrier, defined as the ratio between the kerma before the barrier vs the kerma after?
B(x) = (P/T)d^2/(KUN) K = average unshielded air kerma per patient at 1 m from the source N = # patients per week P= design dose goal T=occupancy factor U = use factor Assumptions if the room has multiple sources: Choose distance from the source that contributes the most. For primary beam, d should be measured from the x-ray tube delivering the primary radiation to that barrier. For barriers struck only by secondary radiation, measure d from the center of the table.
What is a photooncogene?
Codes for proteins that stimulate cell division. Mutated versions are called oncogenes, which can cause excessive proliferation.
Factors that affect radiosensitivity:
Conditional radiosensitivities: dose rate, LET, presence of oxygen High dose rate with low LET increasses sensitivity. High LET means less of a shoulder, more linear cell-survival curve. Fractionation has less effect at high LET. Oxygenation increases lethality in low LET. Inherent factors: Law of Burgunie and Tribondeau: Mitotic rate of cells - higher rate means higher sensitivity Low differentiation means more radiosensitive Cells are most vulnerable in the M phase, G2 phase next, resistant at G1, most resistant at S phase. (Cell phases are G1, S, G2, M)
Steps to take before imaging a pregnant woman?
Determined if another type of imaging that does not use ionizing radiation (US or MR) could give the desired diagnostic and interventional results. Analysis of the stage of gestation, the estimated anticipated fetal dose, the medical indication for the interventional procedure, and the risk of delaying the procedure (which often depends upon the stage of pregnancy).
Deterministic effect versus stochastic effect:
Deterministic effects are not scene before a cutoff threshold. Stochastic effects increase in likelihood with dose, severity of occurrence is independent of dose.
What is gastrointestinal syndrome:
Doses >12 Gy kill intestinal mucosa, causing nausea, vomitting, diarrhea, cramps. Death is ~100% and occurs 3-10 days. Causes greatly diminished capacity to regulate electrolytes and nutrients. Called gastrointestinal sequelae. Bacteria invades intestinal tract simultaneous to white blood cell death.
What is hematopoietic syndrome?
Doses of 0.5-10 Gy full body will kill lots of stem cells in the bone marrow. healhty adults will usually survive <2Gy, most die at >8Gy without bone marrow transplant of infection or hermorrhage from loss of platelets and white blood cells. Anemia from loss of red blood cells. Human LD50/60 = 3.5-4.5Gy without care, 5-6 Gy with care. Effects coincide with ARS
Skin effect thresholds and timings for fluoroscopic exposures:
Early transient erythema: 2Gy, 2-24hr onset Main erythema reaction: 6Gy, ~1.5 wk Temporary epilation: 3 GY, ~3 wk Permanent Epilation: 7Gy, ~3 wk Dry desquamation: 14Gy, ~4wk Moist Desquamation: 18Gy, ~4 wk Secondary ulceration: 24 Gy, >6 wk Late Erythema: 15 Gy, 8-10 wk Ischemic dermal necrosis: 18 Gy, >10 wk Dermal atrophy (first phase): 10 Gy, >12 wk Dermal atrophy (second phase): 10 Gy, >52 wk Telangiectasias: 10 Gy, >52 wk Delayed necrosis: 12 Gy, >52 wk
What possible radiation effects happen at 4-8 wk stages of gestation?
Embryonic death: 250 mGy at 18d, >500 mGy at >50d
Define absorbed dose:
Energy imparted per unit mass by ionizing radiation at a specific point. SI unit is Gy
Personnel dosimeters:
Film badges - dose is not equal to tissue. Use filters to help identify energy deposited. Vulnerable to heat and moisture. Dosimeters with storage phosphors (TLDs): records dose similar to tissue and can be reused. OSLs too, can be reread multiple times before erasing. Range from 100 uSv -10 Sv, reacting to 20 keV - 6 MeV photons, and 0.766 MeV - 5MeV betas. Direct Ion Storage Dosimeter: Uses gas-filled ion chamber with analog memory cell to record storage. Read through USB port. Has brad dose and energy range, unlimited reading by the user, but high initial cost. Can't read beta radiation. Pocket dosimeter: Display dose data immediately. Quartz fiber in air filled cahmber with wire frame with electric charge. Fiber bent away from frame by coulombic repulsio. Radiation neutralizes charge and radiation is measured by fiber movement. Reads >20 keV photons.
Distance to nearest occupied organs (d):
For adjacent wall - <0.3 m From upper floor to floor below: be not >1.7 m above the lower floor For ceiling transmission the distance of at least 0.5 m above the floor of the room above
Ion chamber vs GM counter?
GM counter gives counts vs time while ion chamber provides exposure information vs time run at a lower voltage.
Rad safety detection equipment:
GM counter: CPM Ion chamber: Exposure rates in R/hr - mR/hr range at >20keV
What is the gamma constant?
Gamma constant is the equivalent dose delivered at 1m from the unshielded source. Units are [R*cm^2/(mCi-hr)]
Effective dose from dosimeter readings?
H_effect = 0.18 x H_collar H_effect = 1.5 x H_under apron + 0.04 x H_collar
What possible radiation effects happen at 16wk-term stages of gestation?
Higher exposures can produce growth retardation and decreased brain size and intellect, although the effects are not as severe as occurs from similar exposures during midgestation Minimum lethal dose (from animal studies): >1,500 mGy Minimum dose for severe mental disability: >1,500 mGy Decrease in IQ can occur at lower doses: >100 mGy
What happens if a sentinel event happens? What is the radiation sentinel event?
Hospital must do a root cause investigation and create a plan of action within 45 days. Can, but not required for the hospital to report to the Joint Commission. Should include leadership and the most involved staff members. Numerical measures of success (MOS) determined after 4 months. Prolonged fluoroscopy with cumulative dose >15 Gy to a single field or, Any delivery of radiotherapy to the wrong body region or > 25% above the planned radiotherapy dose.
CTDI method for CT scattered air KERMA (K) calculation:
K = k x (L/Pitch) x (mAs/Rotation) x (CTDI_100/mAs) x (Scan kV/CTDI kV)^2 k_head = 9 x 10^-5 [1/cm] k_body = 3 x 10^-4 [1/cm]
DLP method CT scattered air KERMA (K) calculation:
K_head = k_head x DLP K_body = 1.2 x k_body x DLP N = number of rotations T = slice width per rotation k = scatter fraction per centimeter from NCRP 147 k_head = 9 x 10^-5 [1/cm] k_body = 3 x 10^-4 [1/cm]
Equation for unshielded primary air kerma according to NCRP 147:
K_p(0)=K_p1 (U) N/d^2 o K_p1 = unshielded primary air kerma at 1m / patient o U = use factor o N = # of patients o d = distance from x-ray tube
What is the relationship between the total unshielded kerma, the design dose goal (P), and the occupancy factor (T)?
Kerma <= P/T
Organs and relative radiosensitivity:
Lymphoid organs: high Skin, lens of eye, organs with epithelial cell lining: Fairly high Growing cartilage, growing bone, vasculature: Medium Mature Cartilage, lungs, kidneys, liver, glands: Fairly low Muscle, nerve cells: low
Explain MIRD:
MIRD = Medical Internal Radiation Dose Created by the MIRD committee. Cumulative activity = A = 1.44(Initial Activity)(T1/2_Effect) Absorbed Fraction = energy/organ mass S factor [Gy/Bq-sec or rad/uCi-hr] found in tables in target organ/source organ format Dose from h to k= A*S(organ h to k) total dose is summation of dose from organs h to k Limited by the assumptions of simplistic organs and uniform distribution of dose within organs.
Typical radiation doses and metrics of mammography?
Mean glandular dose, usually 2mGy per view for a standard breast.
Methods of patient dose reduction:
Minimize field size, shield radiosensitive organs if needed, increase SOD, use efficient imaging detectors. Fluoro (difficult cases can give 10+Gy): Use ABC, avoid high level when possible, use last image hold, spread dose to different views if possible, minimize patient thickness in beam, train and credential physicians. CT: Choose appropriate protocol for the patient, use higher kV for large patients, use lower kV for contrast in angeography images (brain), use tube current modulation, iterative reconstruction, minimize scan range, avoid eyes, optimize protocols, ensure auto mA modulation has reasonable mA limits, CTDIvol for Breain perfusion <0.5 Gy, use ECG-gated mA modulation for cardiac retrospective gating. Miscellaneous: Minimize screening exams, scan the correct patient, ensure equipment works properly, perform pregnancy test if necessary, use proper monitors.
What possible radiation effects happen at 8-15 wk stages of gestation?
Most sensitive period for irreversible whole-body growth retardation, microcephaly, and severe mental disability Minimum dose for growth retardation: 250-500 mGy Threshold for severe mental disability: 60-500 mGy Decrease in IQ can occur at lower doses: ~100 mGy Microcephaly >=20,000
What possible radiation effects happen at 3-4 wk stages of gestation?
Most sensitive period for the induction of embryonic death. (100-200 mGy threshold). Anything <50 mGy is unlikely to cause any effects and is indistinguishable from 0.
What regulatory bodies are there for radioactive materials in the US?
NRC: regulates definitions of radioactivity, dose, and standards for workers. Handles agreement states, CFRs, how materials are used and stored. FDA: regulates development and manufacturing of radiopharmaceuticals, manufacturing of x-ray equipment, and receives reports of injuries and/or deaths that equipment may have contributed to. (The joint comission handles sentinel events) Department of transportation: regulates how radioactive materials are transported.
What radiation induced effects in fetuses are shown to be caused by doses of <100 mGy?
None
Common radiation windows, walls, and door shielding materials?
Normal plate glass - Can be heavy if thick. Not good for shielding Lead glass - specify kVp to thickness Lead Acrylic - Soft material that can get scratched Gypsum wall board (Sheetrock) Lead - weight is 64*thickness in inches. Usually 1/32 in to 1/8 in Doors: Wood - Not good shielding If lead is required, the inside of the door frame should be lined with a single lead sheet Mineral core door - core consists primarily of calcium silicate, which has attenuation properties similar to gypsum wallboard
Where are dosimeters placed on the body?
On the torso. If lead is used, on the collar in front of lead with possible second one under lead. Pregnant worker wears 2nd dosimeter at waist level.
What is the p53 gene and what does it do?
P53 is an important tumor suppressor gene. It halts the cell cycle for repairs and pushes the cell to apoptosis if it can't be repaired. 50% of human tumors have P53 gene mutations.
What are the acute skin dose ranges, effects, and timeframes from exposures of 0-2 Gy in the absence of mitigating or aggravating physical or clinical factors:
Potential early transient erythema at 2 Gy, but not much recorded at less than 2 Gy
Define primary and secondary radiation exposure:
Primary radiation is the useful beam from the x-ray tube. Secondary radiation is the scattered radiation from the patient or other objects. Scattered radiation is proportional to field size.
Modifiers of cancer risk?
Quality of radiation (LET) Dose rate and fractionation Age of radiation recipient (younger is higher risk) Sex (women are at greate risk due to ovaries and breast sensitivity) Target organ risk Genetics (such as Ataxia-telangectasia (ATM), a rare recessive gene)
Describe acute radiation syndrome:
REsponse to whole body high acute radiation dose. Has 4 phases: Prodromal phase (first 48hrs): anorexia, nausea, vomiting, diarrhea, fever, lymphopenia, granulocytosis Latent (hours-21 days: Prodromata absent or diminished Manifest illness (hours-30days): Vascular damage, infection, bone marrow depression, leukopenia, thrombocytopenia, GI symptoms Death/recover (hours-60+days)
How does radiation interact with tissue?
Radiation creates energetic electrons if that radiation has enough energy to break the binding energy. Secondary electrons (delta rays) transfer energy to their surroundings with more excitation and/or ionization if energy is sufficient. If not (E<7.4 eV), energy is transfered through vibration, rotation, and collision. Energy is deposited very quickly: ~10^-8 sec
Regeneration vs Repair:
Repair for radioresistant cells. Replaces damaged cells with new cells. Regeneration replaces damaged cells with the same cell.
Relative risk definition:
Risk of exposed population/ risk of unexposed RR = 4 means 4x more likely to have that cancer Excess relative risk = RR-1
How are the reference levels for CT dose set?
Set at the 75%. 75% of doses are below the reference level.
How does ionization damage DNA?
Several interactions within a short distance creates complex/clustered damage with multiple damage sites that are more difficult for cells to repair and may end up repaired incorrectly. Radiation can be direct or indirect. Most of it is indirect. Indirect damage is done by free radicals. Ionization creates free radicals from water: H20+ + H20 = H3O+ + OH (Hydroxyl radical) H20- = OH- + H (Hydrogen radical) Damaging effects of free radicals are enhanced with oxygen since it stabalizes free radicals by binding to them and creating HO2 and inhibiting repair. Lifetime of free radicals are 10^-5 s, ~4 nm, and are the primary cause of damage in low-LET radiation.
What is a spur? What is a blob?
Short range interaction ~4-5nm from a low (~100 eV) energy electron. Accounts for 95% of deposited energy. Blobs are longer but still short interaction (~12 nm) from a slightly higher energy electron (300-500 eV)
Types of chromosomal abberations?
Single break, ring formation from faulty repair of double break, translocation where broken piece of 2 chromosome legs are swapped, 2 centric fragments recombine into a dicentric
What does an optically stimulated luminescence dosimeter consist of?
Strip of aluminum oxide crystalline material sealed in a laminated, light tight paper.
Describe a cell survival curve:
Survival fraction vs dose. Linear quadratic model SF(D) = exp(-alpha x D + beta x D^2) alpha is the linear portion coefficient beta is the quadratic portion coefficient Draw line from 0 dose along quadratic section, alpha x D is above the dotted line, beta x D^2 is below alpha/beta ratio describes cell sensitivity to different kinds of dose - low alpha/beta means larger shoulder and higher survival. D0 describes radiosensitivity under the study. It's the roughly linear part of the cell. Radioresistant cells have higher D0. n = extend the linear part out to the y-axis intercept Dq = draw a horizontal line from 100% survival fraction at 0 dose to the line to find n. Dq is the intercept point.
Define relative biological effectiveness:
Term relating the effeectiveness of the test radiation to the reference radiation. RBE = dose of 250 kV x-rays to produce effect / Dose of test radiation to produce the same effect. 1.5-3 for high energy x-rays vs 250 kV x-rays.
Roughly what is the assumed increase to cancer risk per Gy to a fetus?
The risk is no greater than exposures during early childhood. Cancer is least likely to be induced during or after the third trimester. Assume risk is nontrivial. Reasonable to assume cancer risk is 5-15% per Gy (few times more than general pop = 5% per Gy)
Control dose by controlling what?
Time, Distance, and shielding
What are the goals of radiation protection?
To limit stochastic effects and prevent deterministic effects.
What are the acute skin dose ranges, effects, and timeframes from exposures of 2-5 Gy in the absence of mitigating or aggravating physical or clinical factors:
Transient Erythema (<2wk), epilation (2-8wk), recovery from hair loss (6-52wk)
What are the acute skin dose ranges, effects, and timeframes from exposures of 5-10 Gy in the absence of mitigating or aggravating physical or clinical factors:
Transient erythema (<2wk) Erythema, epilation (2-8wk) prolonged erythema if closer to 10 Gy + permanent partial epilation(6-52wk) Dermal atrophy induration at higher doses (>40wk)
What are the acute skin dose ranges, effects, and timeframes from exposures of 10-15 Gy in the absence of mitigating or aggravating physical or clinical factors:
Transient erythema (<2wk) Erythema, epilation, possible dry or moist desquamation, recovery from desquamation (2-8wk) Prolonged erythema, permanent partial epilation(6-52wk) Dermal atrophy induration, skin likely to be weak; atrophic, telangiectasia (>40wk)
What are the acute skin dose ranges, effects, and timeframes from exposures of >15 Gy in the absence of mitigating or aggravating physical or clinical factors:
Transient erythema, edema, acute ulceration at very high doses (<2wk) Erythema, epilation, moist desquamation (2-8wk) Dermal atrophy, secondary ulceration due to failure of moist desquamation to heal, dermal necrosis at higher doses(6-52wk) Dermal atrophy induration, telangiectasia possible skin breakdown, wound may persist into a deeper lesion (>40wk)
Dose equivalent unit and definition:
Unit is in Sv or rem. Defined as the absorbed dose estimates the relative biological effectiveness of ionizing radiation. H_t = Absorbed dose*W_R W_R is the radiation weighting factor for estimating the relative biological effectiveness of ionizing radiation
Effective radiation dose unit and definition:
Unit is in Sv or rem. Defined as the sum of weighted equivalent doses to specific tissues. Effective Dose = E= Absorbed dose (W_t) W_R W_t is the tissue weighting factor. Fraction of detriment when the whole body is irradiated uniformly. W_R is the radiation weighting factor for estimating the relative biological effectiveness of ionizing radiation
Workload Equation and meaning:
W = N*W_norm N = # of patients per week W_norm = Average workload per patient Time integration of total mA in units of [mA-Minutes]. Air kerma is linearly proportional to workload. Assume a high workload at a single high kVp
What are some factors for radiation effects to the fetus?
o Age: Rad risks are most significant during preimplantation and organogenesis and portions of the first trimester (progressively less as pregnancy advances) o Position/depth: depth is less as age increases, depth changes with bladder fill (can take advantage of this) o Dose: Higher dose can à embryonic death, congenital malformations, growth retardation and neurological detriment (>1 Gy results in high lethality) There is no evidence that rad dose < 100 mGy is associated with adverse effects
Fetal doses of typical diagnostic procedures (mean):
x-ray: Abdomen - 1.4 mGy Thoracic spine, chest, and skull - <0.1 mGy Lumbar spine and urogram - 1.7 mGy Pelvis - 1.1 mGy Fluoro: Barium - 1.1 mGy Barium enema - 6.8 mGy CT: abdomen - 8 mGy chest - 0.06 mGy Head - <0.005 mGy Lumbar spine - 2.4 mGy Pelvis - 25 mGy
What is the algebraic solution to the barrier thickness, x_thickness, given by NCRP 147:
x_thickness = 1/(αγ) ln[ ( (NTK/(pd^2) )^γ + β/α )/(1+ β/α)] o Where α, β, γ depend on the material of the barrier and the workload distribution as a function of kVp
Consider some rules of thumb when treating a pregnant patient:
· If patient pregnant, consider: waiting, using non-ionizing modality · If scan necessary: exclude fetus from primary beam, reduce dose mode or collimation, optimize technique to fetus (shielding on pelvis not shown to be useful - most dose scatter within mother) · Estimating dose to the fetus: o Rule of thumb: fetal dose is 1/3 the entrance dose for average patient o If initial quick estimate (non-abd/pelv typically <1 mGy, abd/pelv < 50 mGy) is over 10 mGy, must do detailed calculation using established method o Large amount of uncertainty in even detailed calculations (20-80% depending on method)
The following documentation shall be maintained on a permanent basis by the operator of the facility:
• Shielding design data including assumptions and specifications • Construction, or as-built, documents showing location and amounts of shielding material installed • Post-construction survey reports • Information regarding remedies, if any were required • More recent reevaluations of the room shielding relative to changes (in utilization, etc.) that have been made or are still under consideration
