Radiation Protection
Review of Units of Measurements
Protection for Patient and Personnel
Review of Radiobiology
Follows the ARRT Content Specifications
Sources of Radiation Exposure
Natural or background - ground, cosmic, naturally occurring isotopes, etc.
Artificial or man-made - Medical and dental largest contributor to population dose
Units of Measurement - Know traditional and
Standard International UnitsRoentgen (R) - traditional unit of exposure in air - equipment related [x and gamma rays]
Coulomb/Kg or C/Kgrad (r) - traditional unit of absorbed dose [all]
rem - traditional unit of dose equivalent [x, beta, gamma]
Seivert (Sv)
Curie (Ci)
- measure of radioactivityBecquerel (Bq) = in Nuc Med
Detection Methods
Personnel Field Instruments
Film Badges - month
photographic film
TLD - 3 months
$ but very accurate
Ionization chamber
pocket dosimeter
drifts / not accurate
Larger one for NM or more industrial
Ionization Counter
Cutie Pie,Geiger Counter
spills, more industrial
Scintillation detector
more technical use
used in CT,NM
RT personnel use film badges
Monitoring Agencies
NCRP -National Council on Rad Protection
dose limitations control
DRH - Devices for Radiological Health
radiation control (more equipment related)
NRC - Nuclear Regulatory Commission - radiation protection standards (formerly- Atomic Energy Comm)
Maryland State Dept. Health & Hygiene
EPA - Environmental Protection Agency
more industrial application related matters
Recommendations for Dose
ALARA - As Low As Reasonably Achievable for patient and occupational worker
Cumulative Dose Limit for Occupational Worker - simply your age x 1 rem
ie. 47yo male RT, 47 rem
Embyro or fetus -- 50mrem/month or 500 mrem total
Member of public frequently, exposed 100mrem
Interactions with Matter
Coherent ( Classicial or Thompson) scattering: < 30kVp
Photoelectric Effect 30-150 kVp
Compton’s Scatter: 30-150 kVp
ie. 70kVp 40% PE and 60% Compton
vs 100kVp 10% PE and 90 % Compton
Pair Production and Photodisintegration : MeV as in Rad Therapy
Estimated Patient Doses
Skin - TLD 15, 000mrem and extremities 30,000 mrem
Gonad -- genetic responses at 20rads/yr
Bone Marrow (mean) - rad induced leukemia 100 rad/yr
Gonadal and bone doses are estimates
!Estimated Doses
Fluoroscopic are harder to measure
2rad/mA/minute
remember patient becomes the hazard since the scatter is what gets the radiographer
Exams with higher patient doses are:
Fluoro
Angio
Portables
General - around pelvic region, hip femur, lumbar, coccyx, sacrum
Cardinal Principles
Time : time, dose OR ¯ time, ¯ dose
Distance: distance, ¯ dose OR if you conversely ¯ distance, dose (don’t forget the inverse square law or direct square law)
Shielding: reduces dose as much as 95% in male patients
Patient Protection
Cardinal Principles
time, distance, shielding
Exposure Factors
kVp, mA, time, distance
directly related
kVp - ¯ interactions
¯ time - ¯ dose
fluoro time -keep it short
mA and ¯ (fast) time
Filtration - inherent
0.5mm al <50kVp
1.5mm al 50-70kVp
2.5mm al >70kVp
Film Screen Combo
Beam limitation
PBL - automatic collimation
Cones
Cylinders
aperture diaphragms
¯ field, scatter, dose
Avoid Repeats
techniques charts
good communication
restraining devices
good QA program
Patient Protection - continued
Shielding - not < 0.25mm Pb
long bones in peds
all eyes
gonadal - 5cm primary
flat rubber lead strips
shadow shield
shaped or cup
eye shields
If patient holds cassette, Pb glove needs to be 0.5 mm to protect hand
Air Gap technique
High Dose to
Gonadship upper femur
pelvis lumbar
lumbo-scaral
abdomen
sacrum coccyx
S-I Joints
BE, IVP, Cysto, Hystero
Personnel Protection
Cardinal Principles
Time, Distance, Shielding
Protective wear
Pb aprons 0.5mm =
Pb gloves 0.25mm =
thyroid - ¯ dose 10% & 6mrad per exam
Pb glasses 0.75mm
¯ dose 98%
Pb sterile gloves
Barriers - 7" high
primary 1/16th inch
secondary 1/32 inch
Pb glass port
mobile in OR
Mobile exposure cord length - no less 6’
Personnel Protection Continued
Never hold Patients - use immobilization devices
Wear monitoring devices
film badge
TLD
Pocket dosimeter
Fluoro equipment - apron on tower, bucky slot cover, fluoro timer
Clear room when doing portables or provide with Pb apron
Stand 2 m from table
Pregnancy
Radiographer
self disclosure voluntary
fetus 50mrem per month or 500 mrem or 5mSv over term
Baby badge at waist
0.5mm Pb aprons are 88% effective > 70 kVp
Patient
ask about LMP
ALARA
double shield or limit exam views
10 day rule for high dose exams
Rad Protection - Equipment
Control panel: light, meters and sound
SID: within ± 2% variance
PBL: within ± 2% of SID
Beam alignment
Filtration: 2.5mm Al equivalent total
Reproducibility: output = , not to exceed 5%
Linearity: intensity = across mA stations, not be exceed 10%
Personnel shield: short cords so exposures are made behind 7" barriers
Rad Protection - Equipment
Mobile C-Arm: not < 12" (30cm) source to tabletop distance
Stationary Fluoro:not < 15" (38cm) source to tabletop distance
Primary Barrier: IA assembly 2mm Pb equivalent when >125kVp (usually 80-120 kVp fluoro)
Filtration: 2.5mmAl total just in overhead tube; <100mR/Hr leakage at 1 meter
PBL on Fluoro tower: borders on monitor when IA is 14" from tabletop
Exposure switch: "Dead man" - intermittent ¯ dose
Rad Protection - Equipment
Bucky Slot Cover: 5cm wide at gonadal level and 0.25mm Pb thick
Protective Apron on Tower: 0.15- 0.25mm Pb between patient & operator
Cumulative Timer for Fluoro: 5 min/audible
X-Ray Intensity: should not >2.1R/min at tabletop per mA at 80 kVp
Dose Rate: must not > 10R/min maximum, should not 5
Front loaded cassette vs back load: front less dose
Spot cassette vs spot film camera -- dose to patient 3x more for cassette over camera
RADIOBIOLOGY
In addition to the technical side, we must understand the biological effects!
Characteristics of Radiation
Physical
LET - efficiency of radiation to produce excitation and ionization ( energy deposit per unit path length)
LET of dx is 3 keV/m m
RBE - Relative Biological Effectiveness
Biological Aspects
Review the mitosis and meiosis cycles
The most sensitive time for DNS is G2 and rest of mitotic stages (least during G1 and Synthesis)
Keep in mind that in meiosis, DNS replicates only once
What about other factor affecting cellular response?
Laws of Sensitivity
High mitotic activity -- more sensitive
Cell differentiation -- less, more sensitive
Long dividing future -- more sensitive
All these Bergonie and Tribondeau
Biological Stress
Pre/post irradiation conditions
Chemicals -- enhancers, protectors
Ancel and Vitemberger -- more environment related
Effects---
Direct - photon strikes DNA --breaks in ladder either rungs or side rails
Indirect - photon strikes water -- most abundant so most likely to happen more frequently
Target Theory -- variations, but striking a critical DNA area where lethality occurs immediately or may take two hits to achieve death
Cell survival curves - curve representing the dose and proportion of cells surviving
Mean Survival Curves
Relationship between the dose and number of cells that survive
Lethal Dose
human LD 50/60 -- 350 rad
previously 50/30 - Chernobyl changed figures
Dose Response Relationships
Linear, non-linear
Threshold or non-threshold
(non-stochastic) (stochastic, random)
We practice by Linear, non-threshold
Cellular Responses
Interphase death
Division Delay
Reproductive failure
Stages of Response
Dose Dependent
Prodromal -- NVD
Latent
Manifest
hematologic --dose between 100-1000
200-600/200-1000
GI syndrome - dose between 1000-5000
600-1000
CNS - dose > 5000
Recovery or Death
Radiation Reduced Malignancy
Historical populations
Dose related
Risks associated
20% population USA will die of Ca
how do you tell if rad caused?
Children? Leukemia is common
In Utero -- Fetal Irradiation
neonatal death - 2-3 week of gestation
malformations
growth stunting
congential defects - functional defects after week 20
cancer induction
Week 4-11 severe abnormalities, especially CNS and skeletal, while 11- 16 mental retardation & microcephaly