Dose trivia Flashcards
absorbed dose unit
Gy (J/kg)
What is the threshold for permanent sterility in males from an acute exposure, approximately?
6 Gy
Individuals who work in facilities in which radiation sources are used but whose responsibilities do not include exposure radiation are permitted to be exposed up to how many mrem per year?
100 mrem whole body
What does the radiation unit of absorbed dose measure?
Amount of energy absorbed per unit mass from ionizing radiation
The threshold dose for the main erythema reaction in human skin is ?
5 Gy The terms as defined by the International Commission on Radiological Protection (ICRP) include an early transient erythema seen a few hours after doses of 2 Gy. The main erythema reaction is at ~ 10 days and is secondary to inflammation and cell death of the basal epidermal layer and occurs at ~ 5 Gy. A late erythema can be seen 8-10 weeks after exposure and is bluish secondary to ischemic changes (~ 15 Gy).
The threshold dose for the early transient erythema in human skin is ?
2 Gy The terms as defined by the International Commission on Radiological Protection (ICRP) include an early transient erythema seen a few hours after doses of 2 Gy. The main erythema reaction is at ~ 10 days and is secondary to inflammation and cell death of the basal epidermal layer and occurs at ~ 5 Gy. A late erythema can be seen 8-10 weeks after exposure and is bluish secondary to ischemic changes (~ 15 Gy).
The unit of kinetic energy released in a mass (kerma) is a measure of?
Kinetic energy released in a mass (kerma) is a measure of the total initial kinetic energy of all charged particles liberated by uncharged particles per unit mass. It has units of J/kg, or Gy.
CTDI definition
CT dose index The CT dose index (CTDI) is a measure of the dose per slice as estimated with a 16 cm or 32 cm acrylic phantom as measured over a 100 mm length. CTDIvol takes into account the effect of mAs, kVp, and pitch as well as the difference in dose at the periphery and center of the phantom (CTDIvol = (1/3 x CTDI100 [center] + 2/3 x CTDI100 [periphery])/pitch).
Is CT scan length taken into account with CTDI or DLP?
DLP (dose length product) DLP = CTDvol x scan length
Radiation dose increases _____________with scan length
linearly
regulatory dose for fluoro (no high level control)
87 mGy/min (10 R/min)
regulatory dose for fluoro (high level control)
176 mGy/min (20 R/min)
What parameter must be set for High level control?
an audible alarm must be on when HLC is used
operator dose at 1 m from fluoro table
0.1% of what the patient gets
operator regulatory dose limit
50mSv/yr
fetus dose limit of operator
0.5mSv per mo
permanent epilation dose
7 Gy
at what dose does a physicist need to review the case?
> 5 Gy
Dry desquamation dose
13 Gy
Moist desquamation dose
18 Gy
Secondary ulceration
24 Gy
13 Gy
Dry desquamation dose
18 Gy
Moist desquamation dose
24 Gy
Secondary ulceration
CT Accreditation program developed by the ACR has established diagnostic CT reference values. What is the CTDvol for a routine adult abdomen?
25 mGy
According to Nuclear Regulatory Commission regulations, what is the annual dose limit for occupationally exposed individuals for the whole body, lens, and extremities?
5 rem to the whole body 15 rem to the lens 50 rem to the extremities
The maximum dose an individual member of the public may receive from the release of patients injected with radioactive materials (e.g., thyroid ablation patients)
5 mSv (500 mrem) is the maximum dose an individual member of the public may receive from the release of patients injected with radioactive materials.
The dose limit to a general member of the public from activities performed involving the use of radiation
1 mSv (100 mrem)
difference between CTDIw and CTDIvol
Weigthed CTDI takes into account the difference between the dose at the periphery (about double the center) and dose at the center. It is calculated by 1/3 the central CTDI + 2/3 the periphery CTDIw is expressed in mGy (no volumetric or length data - JUST DOSE) Volume CTDI (CTDIvol) is obtained by divided CTDIw by the pitch (CTDIvol = CTDIw/pich)
CTDIw and CTDIvol unit
mGy
equation for CTDIw
1/3 central CTDI + 2/3 peripheral CTDI
DLP equation
DLP = CTDI vol x length of scan
CTDIvol equation
CTDIw/pitch
units of DLP
mGycm
units of effective dose for CT
Sv
equation for effective dose in CT
effective dose = k x DLP
size of CT phantoms1
32 cm adult; 16 cm peds
CTDI numbers are based on:
CT phantoms. body phantom is 32 cm, peds phantom is 16 cm
ACR reference values CTDIvol: head, adult abdomen, peds abdomen
75mGy for head; 25 mGy for adult abd; 20 mGy for peds abd (5 yo) Ference dose is set by the ACR at the 75th percentile, and doses above this level should be investigated. These values are different from average dose
if patient larger than CT phantom, dose is __________estimated
if patient larger than CT phantom, dose is OVER estimated
if patient smaller than CT phantom, dose is __________estimated
if patient smaller than CT phantom, dose is UNDER estimated
dose is UNDER estimated when patient is _______ than the CT phantom
dose is UNDER estimated when patient is smaller than the CT phantom
dose is OVER estimated when patient is _______ than the CT phantom
dose is OVER estimated when patient is larger than the CT phantom
average dose in adult head CT
60 mGy
average dose in adult abd CT
20 mGy
average dose in peds abd CT
15 mGy
effective dose in adult head CT
1-2 mSv
effective dose in adult abd CT
8-11 mSv
dose of 1 CT chest is equal to about _____ PA CXRs
1 CT = 100 CXRs
CT of extremity effective dose
< 1mSv (super duper low) because extremities don’t contain any radiosensitive organs
embryo dose in CT A&P
30mGy
when is individual dose monitoring mandated?
when the occupational dose is >10% the annual dose limit of 500 mrem
risk of radiation induced cancer per dose in adult vs child
adult: 5% per Sv. child: up to 15% per Sv
maximum annual total effective dose equivalent for a worker under 18
NRC annual occupational dose limit for minors is 10% of adult dose limits. For total effective dose equivalent for adults is 50 mSv (0.05 Sv). The limit for a minor is 5 mSv (0.005 Sv) 5mSv is the same limit as for a fetus
32 cm acrylic phantom is placed in the CT gantry. The following measurements were obtained with the pitch set at 1.25: CTDI periphery = 30 mGy and CTDI center = 15 mGy. What is the CTDIvol?
20 mGy CTDIw is calculated as (1/3) CTDIcenter + (2/3) CTDI periphery. The CTDIvol = CTDIw/Pitch (1/3)(15) + (2/3)(30) = 25 25/1.25 = 20
background radiation
3 mSv (300mrem)
dose limit to member of general public
1 mSv (100 mrem)
Total effective dose limit for a radiation worker
50 mSv (500mrem)
dose limit for a radiation worker’s lense
150 mSv
dose limit for a radiation worker’s extremity
500mSv (50,000 mrem, 50 rem)
(1 Sv = 100 rem)
1 Sv = ________rem
1 Sv = 100 rem
1 mSv = ________mrem
1 mSv = 100 mrem
100 mrem = _______mSv
100 mrem = 1 mSv
100 rem = _______Sv
100 rem = 1 Sv
estimated absorbed dose to fetus from a routine abdomen pelvis
25 mGy
2.5 mGy.
Use inverse square law, the dose at point B will be 4 times less than the dose at point A since the distance was doubled. So, 10/4 = 2.5 mGy
a medical event must be reported if:
a pregnant patient inadvertently adminstered I-131 for Grave’s disease.
at what gestational age would the infant be at greatest risk for radioactive iodine-induced creatism
10-12 weeks
29 yo patient who is 10 weeks pregnant undergoes CT scan with estimated fetal absorbed does of 25 mGy. Increased risk of:
2x increased risk of cancer at 25 mGy
- For dose < 50 mGy –> no risk of birth defect, intellectual disability or fetal death
- > 100 mGy higher increase in adverse effects
- 1-2 weeks (preimplantation period) : there is an increased risk of death.
- 3-8 wk (organogenesis): increased risk of severe birth defects
- 9-15 wk: increased risk of mental retardation
