Xoran P1 Basics

Slide1: 

Xoran Radiation Safety Part 1 Radiation Basics

Outline: 

Outline X-ray production and interactions What is dose? (units) Biological effects and risk Naturally occurring radiation

What are X Rays?: 

What are X Rays? X rays are Electromagnetic waves of short wavelength High energy photons (just like light) Photon Properties: No charge No mass Travel at the speed of light

Electromagnetic Waves : 

Electromagnetic Waves Low High ENERGY Radio waves Microwaves Radar Infrared Visible light Ultra-violet X-ray Gamma-ray Non-ionizing radiation Ionizing radiation

How are X rays produced?: 

How are X rays produced? Electrons are accelerated across a gap with high voltage Electrons hit Tungsten target and are quickly deflected and decelerated Accelerated charges radiate electromagnetic waves (x rays) Electrons also interact with atomic electrons creating characteristic x rays

Bremsstrahlung Radiation: 

Bremsstrahlung Radiation Produced from the deceleration/deflection of the electrons near the atomic electric field of the anode atoms. These electromagnetic waves are emitted in a continuous spectrum of energies. Bremsstrahlung means “ braking radiation” in German.

Characteristic X Rays: 

Characteristic X Rays Produced when high energy electrons knock an inner atomic electron out of its orbit. Higher orbital atomic electrons transition to fill the vacancy and release the remaining energy in the form of an x ray.

Electron Interactions: 

Electron Interactions Bremsstrahlung Photons Characteristic X Ray

X-ray Tube Diagram: 

Anode (+) Cathode (-) Electrons (current “I”) Target X-rays Tube Potential “U” (for MiniCAT 120kVp) X-ray Tube Diagram

X-Ray Tubes: 

X-Ray Tubes Fixed anode (VCT) Rotating anode (MDCT)

X-Ray Spectrum: 

X-ray energy Relative Intensity Characteristic X-rays Continuous X-ray (Bremsstrahlung) EMAX (for MiniCAT = 120 keV) X-Ray Spectrum

X-Ray Filtration: 

X-Ray Filtration Beam shaping filter (bowtie) allows for a more constant signal at detectors Some copper or aluminum flat filters may also be utilized More intense beam at center + More attenuation by patient at center Evens out signal at detectors

Filtered X-Ray Spectrum: 

X-ray energy Relative Intensity Characteristic X-rays Continuous X-ray (Bremsstrahlung) EMAX (for MiniCAT = 120 keV) Filtered X-Ray Spectrum

X-Ray Tube Current and Voltage: 

X-ray energy Relative Intensity X-ray energy X-ray energy X-ray energy Relative Intensity Relative Intensity Relative Intensity Increasing Tube Current Increasing Tube Potential (Voltage) X-Ray Tube Current and Voltage

X-ray Interaction with Matter: 

X-ray Interaction with Matter X-ray Tube Scattered X-ray Absorbed X-ray Transmitted X-ray

Quantifying amounts of radiation: 

Quantifying amounts of radiation Exposure Dose 3. Dose equivalence 4. Effective Dose

Quantifying radiation- light analogy : 

Quantifying radiation- light analogy Light is another form of electromagnetic radiation Exposure (Roentgen)- how much light is emitted Dose (rad, rem, gray)- how much light is absorbed by a person

Exposure – Roentgen (R): 

Exposure – Roentgen (R) Measures radiation exposure in air number of ions produced in air x-ray output from machine Defined as the amount of X-rays or gamma-rays that will generate 2.58E-4 coulombs/kg-air = [charge / mass of air] Only applicable to X-ray/gamma-ray field.

Absorbed Dose, D – Rad (Gy): 

Absorbed Dose, D – Rad (Gy) Measures absorbed dose, D Rad stands for Radiation Absorbed Dose. Definition: 1 Rad is the amount of radiation that will deposit 0.01J of energy in a kilogram of material (tissue, air, shielding material …etc). Can be used for any kinds of radiation. Rad is a traditional unit for absorbed dose. International Unit (SI unit) for absorbed dose is Gy (gray). Conversion is 1 Gy = 100 rad.

Equivalent Dose, H- rem (Sv): 

rem stands for Roentgen Equivalent Man Obtained by multiplying mean absorbed dose from radiation R in a tissue or organ T, and radiation weighting factor wR for type of radiation. HT = ∑ (wR x DT,R) For X-rays, weighting factor is 1. Thus, for X-rays, 1 rem = 1 rad. rem is a traditional unit, SI unit is Sv (sievert). Conversions: 1 Sv = 100 rem; 1 rem = 10 mSv Equivalent Dose, H- rem (Sv)

Radiation Weighting Factors: 

Radiation Weighting Factors

Units – Conversion: 

Units – Conversion 1R = 0.93rad (tissue), 0.97rad(bone), 0.87rad(air) For a quick estimation of exposure, it is often approximated that 1R=1rad=1rem.

Effective Dose (mSv): 

Effective Dose (mSv) Sievert is also used to express effective radiation dose The risk of cancer induction from an equivalent dose depends on the organ receiving the dose. dose adjusted for type of radiation, partial vs. whole body exposure, & radiosensitivity of organs exposed

Effective Dose (mSv): 

Effective Dose (mSv) The effective dose is calculated by determining the equivalent dose to each organ irradiated and then multiplying this equivalent dose by a tissue-specific weighting factor for each organ or tissue type. These products of equivalent dose and tissue weighting factor are then summed over all the irradiated organs to calculate the effective dose: E = ∑ (wT x HT) We will use effective radiation dose whenever possible

Determining Effective Radiation Dose: 

Determining Effective Radiation Dose TLD place holders RANDO Head Phantom Measurement Protocol as per ICRP Report #103

Tissue Weighting Factors: 

Tissue Weighting Factors

Effective Dose for MiniCAT: 

Effective Dose for MiniCAT E = ∑ (wT x HT)

Other Measurements : 

Other Measurements A number of special dose quantities have been developed to characterize the doses associated with CT and compare different CT scanners They serve primarily as surrogate measures due to relative ease of calculation They are: Computed Tomography Dose Index (CTDI), "weighted" CTDI (CTDIW), "volume" CTDI (CTDIVOL), "multiple scan average dose" (MSAD) and "dose-length product" (DLP) Sometimes, the exposure (mAs) is used as a surrogate expression for a dose All of the above should be used with caution as can be misleading without the proper context.

CTDI, DLP, MSAD: 

CTDI, DLP, MSAD CTDIw = 1/3 center + 2/3 periphery CTDIvol = CTDIw/pitch DLP = CTDIvol* irradiated width MSAD is the average radiation dose over the central scan of a CT study consisting of multiple parallel scans

CTDI: 

CTDI CTDI- integrated dose, reported in most literature for single and multi-slice CT, but not defined for VCT (rad or mGy) CTDI originated for single-slice CT For MDCT, useful for comparing “dose” from different techniques CTDI makes little sense for VCT, since the beam exceeds the chamber length This is an area of current discussion in the scientific community

Ionization: 

Ionization Ionization Atom Electron Ionizing Radiation Ion More Reactive !! Biological Effect

Biological Effects: 

Biological Effects The deposition of energy to the object (body) by the absorbed and scattered X-rays is the basis for biological effects of X-ray radiation. X-ray has a capability to go through skin layers and deposit its energy to the cells deep inside the body. X-ray has enough energy to ionize atoms, which construct molecules. These ions can break chemical bonds within some critical biological molecules (e.g. DNA)

Biological Effects- Radiation Damage: 

Biological Effects- Radiation Damage Direct: radiation directly ionizes DNA Indirect: radiation ionizes water & produces free radicals: H* & OH* (single e- in outer shell & very reactive). Migrate to target & disrupt bonds, create lesions (e.g., DNA strand breaks or base damage). Responsible for > 95% of damage. Presence of O2 ↑ life of free-radicals, => ↑ risk of damage. Antioxidants ↓ risk (eat your vegetables).

Biological Effects: 

Biological Effects In some cases, those damaged cells are able to repair themselves. However, when high dose or high dose rate exposure may create non curable damage. When cells are not recovered, this damage can cause cell injury or even cell death. The effects may passed to daughter cells (with damaged characteristics). The division of this damaged cell may be the first step in tumor/cancer development. If enough cells in a particular body organ are damaged, the function of the organ may be impaired.

Biological Effects: 

Sensitivity Low High Muscle, Joints, Central nerves, Fat Skin, Inner-layer of intestines, Eyes Bone marrow, Lymph system, Reproductive organs Typically young and rapid growing cells are more sensitive to the radiation than mature cells. When cells divide the DNA is “unpacked” and vulnerable. Biological Effects

Results of DNA Damage: 

Results of DNA Damage Repair Cell death Rapid cell growth Genetic damage Most frequent Very rare DNA double-strand breaks (due to x-ray or free-radical interactions) are less easily repaired, & occasional misrepair can lead to point mutations, chromosomal translocations, & gene fusions all of which are linked to the induction of cancer. (Brenner & Hall NEJM 2007;357;2277

Radiation Risks: 

Radiation Risks Cancer, genetic defects Stochastic (No dose threshold) All or none. (Need change in a single cell) Probability ↑ with ↑ dose Severity does NOT ↑ with ↑ dose Cellular Injury Nonstochastic (deterministic) Has a threshold. (Need changes in many cells) Probability & severity both ↑ with ↑ dose above threshold Like sun burn- has a threshold & longer you are in the sun, the worse the sun burn. Examples: cataracts, radiation-induced erythema (skin burn), radiation induced epilation (hair loss)

Stochastic Effects: 

Stochastic effects are associated with long-term, low-level (chronic) exposure to radiation. Cumulative Cancer is considered by most people the primary health effect from radiation exposure. Mutations (changes in DNA) can occur. Sometimes the body fails to repair these mutations or even creates mutations during repair. The mutations can be genetic mutations  and passed on to offspring. http://www.epa.gov/radiation/understand/health_effects.html Stochastic Effects

Stochastic Effects: 

Stochastic Effects Radiation dose determines probability of effect not severity Radiation induced effects are indistinguishable from non-radiation induced effects

Deterministic Effects: 

Deterministic Effects Non-stochastic effects appear in cases of exposure to high levels of radiation.  Many non-cancerous health effects of radiation are non-stochastic. Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function.

Is any amount of radiation safe?: 

Is any amount of radiation safe? There is no firm basis for setting a "safe" level of exposure above background for stochastic effects. Many sources emit radiation that is well below natural background levels. This makes it extremely difficult to isolate its stochastic effects. Some scientists assert that low levels of radiation are beneficial to health (this idea is known as hormesis). However, there do appear to be threshold exposures for the various non-stochastic effects. http://www.epa.gov/radiation/understand/health_effects.htm

Radiation Risk: 

Radiation Risk Data are available to support increased, decreased, or no risk of cancer from low dose radiation Few of these data are taken from diagnostic imaging exposure All of the data are open to interpretation and subjectivity

Radiation Risk: 

Radiation Risk Committee on Biological Effects of Ionizing Radiation (BEIR) estimates risk associated with radiation exposure “A comprehensive review of the available biological and biophysical data supports a “linear no threshold” (LNT) risk model – that the risk of cancer proceeds in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans” LNT is widely accepted and gives conservative estimate of risk

Linear No-Threshold Model: 

Linear No-Threshold Model Dose Risk LNT

Radiation Risk: 

Radiation Risk “Epidemiological studies have been carried out to determine the possible carcinogenic risk of doses lower than about 100 mSv, and they have not been able to detect statistically significant risks” French Academy of Sciences “Recent radiobiological data undermine the validity of estimations based on the LNT in the range of doses lower than a few dozen mSv” National Academy of Medicine

Radiation Risk: 

Radiation Risk “There is substantial and convincing scientific evidence for health risks following high-dose exposures. However, below 50-100 mSv, risks of health effects are either too small to be observed or are nonexistent” Health Physics Society

Radiation Risk: 

Radiation Risk “The Society has concluded that estimates of risk should be limited to individuals receiving a dose of 5 rem in one year or a lifetime dose of 10 rem in addition to natural background. Below these doses, risk estimates should not be used; expressions of risk should only be qualitative emphasizing the inability to detect any increased health detriment (i.e., zero health effects is the most likely outcome”) Health Physics Society

Industry Risks: 

Industry Risks http://www.physics.isu.edu/radinf/risk.htm

Risk from Radiological Procedures: 

Risk from Radiological Procedures http://www.fda.gov/cdrh/ct/risks.html

Patient Effective doses in CT and radiographic examinations: 

Patient Effective doses in CT and radiographic examinations Information abstracted from ICRP Publication 87 http://www.icrp.org/downloadDoc.asp?document=docs/ICRP_87_CT_s.pps

Risk vs. Reality : 

Risk vs. Reality Patients may be misinformed about the risks of radiation For a CT exam with an exposure of 10 mSv, the increased risk of a fatal cancer is 1/2000. The natural risk of fatal cancer in the US population is about 1/5 (about 20%). 20%  20.05% Radiation in Movies Spiderman Incredible Hulk Teenage Mutant Ninja Turtles Benefits outweigh small risk

Pregnancy and Radiation: 

Pregnancy and Radiation There are radiation-related risks throughout pregnancy that are related to the stage of pregnancy and absorbed dose Radiation risks are most significant during organogenesis and in the early fetal period, somewhat less in the 2nd trimester, and least in the 3rd trimester Information abstracted from ICRP Publication 84 http://www.icrp.org/downloadDoc.asp?document=docs/ICRP_84_Pregnancy_s.pps

Pregnancy and Radiation - CNS: 

Pregnancy and Radiation - CNS During 8-25 weeks post-conception the CNS is particularly sensitive to radiation Fetal doses in excess of 100 mGy can result in some reduction of IQ (intelligence quotient) Fetal doses in the range of 1000 mGy can result in severe mental retardation and microcephaly, particularly during 8-15 weeks and to a lesser extent at 16-25 weeks Information abstracted from ICRP Publication 84 http://www.icrp.org/downloadDoc.asp?document=docs/ICRP_84_Pregnancy_s.pps

Pregnancy and Radiation – Doses: 

Pregnancy and Radiation – Doses Information abstracted from ICRP Publication 84 http://www.icrp.org/downloadDoc.asp?document=docs/ICRP_84_Pregnancy_s.pps

NCRP Report 54, page 7: 

NCRP Report 54, page 7 Noting that the excess risk of adverse effects arising from doses below 10 rad probably is not statistically detectable in experiments involving manageable numbers of animals, one must decide on a level above which scheduling is indicated. Doses below 5 rad to the human embryo-fetus are considered by many to represent an acceptable risk when compared to the potential medical benefit of the examination to the patient.

Pregnancy and Radiation: 

Pregnancy and Radiation Should have written procedure Ask female patients of child-bearing age, “Are you or may you be pregnant?” Extremely low dose to abdomen for head CT NCRP recommends no action below 5 rad

Natural Background Radiation in USA: 

Natural Background Radiation in USA Atlantic and Gulf Coastal Plain 1.05 mSv/yr Middle America 1.2 mSv/yr Rocky Mountain Plateau 1.45 mSv/yr Denver, Colorado 1.65 mSv/yr Population-weighted average 1.09 mSv/yr Exclusive of Radon (NCRP 45 and 94)

Natural Background Radiation in USA: 

Natural Background Radiation in USA Radon 2mSv Average Natural Background 3 mSv/yr Internal (K-40) 0.4 mSv

Natural Background and Man-Made Radiation in USA: 

Natural Background and Man-Made Radiation in USA Total Exposure rate of the average U.S. resident is 3.6 mSv /year. Natural 82% Man-Made 18%

Preventive measures: 

Preventive measures Know X-ray beam status at ALL TIMES ! Use safety features (shielding, shutter, warning sign, etc.) Do not place any part of your body in the beam. Make sure the beam is off when maintaining the scanner. Do not operate the device if you are not trained/supervised by trained personnel. MiniCAT has an FDA-mandated auto-shutoff at 44 seconds (110% of nominal exposure)

ALARA: 

ALARA As Low As Reasonably Achievable Radiation protection philosophy which should be applied to maintain any dose at levels as low as are practicable given the objective

Review: 

Review Part 1 Basics Part 2 Principles Part 3 Practical Issues

Electromagnetic Waves : 

Electromagnetic Waves Low High ENERGY Radio waves Microwaves Radar Infrared Visible light Ultra-violet X-ray Gamma-ray Non-ionizing radiation Ionizing radiation

Electromagnetic Radiation: 

Electromagnetic Radiation Ionizing Non-ionizing

Radiation Units: 

Radiation Units Exposure Roentgen- R Dose Gy (rad) Effective Dose Sv (rem) CTDI Gy (rad)

Linear No-Threshold Model: 

Linear No-Threshold Model Dose Risk LNT

Radiation Dose and Risk: 

Radiation Dose and Risk http://www.fda.gov/cdrh/ct/risks.html