7 Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous to living tissue.1913
8 Interactions of X-rays with matter No interaction; X-ray passes completely through tissue and into the image recording device.Complete absorption; X-ray energy is completely absorbed by the tissue. No imaging information results.Partial absorption with scatter; Scattering involves a partial transfer of energy to tissue, with the resulting scattered X-ray having less energy and a different trajectory. Scattered radiation tends to degrade image quality and is the primary source of radiation exposure to operator and staff.
10 Coherent ScatteringAlso called: Classical scattering or Thompson scatteringOccurs with energies below 10 keVIncident x-ray interacts with an atom of matter, causing it to become excited. Immediately the atom releases this excess energy and the scattered x-ray.
11 Coherent ScatteringThe wavelength is equal to the incident x-ray or equal energy.The only difference is the direction of travelEnergy in = Energy out - Only changes is direction
13 Classical (Coherent) Scattering Excitation of the total complement of atomic electrons occurs as a result of interaction with the incident photonNo ionization takes placeElectrons in shells “vibrate”Small heat is releasedThe photon is scattered in different directionsNo loss of E
14 Thompson scatterOccurs primarily with low energy x-rays. Classical will occur throughout the diagnostic range.Coherent contributes slightly to film fog and reduces image contrast.
15 Compton Effect or Compton Scattering Occurs throughout the diagnostic imaging rangeThe incident x-ray interacts with the outer electron shell on an atom of matter, removing it.It not only causes ionization but scatters the incident x-ray causing a reductions in energy and the change of direction.
16 COMPTONSCATTERING –OUTER SHELL ELECTRON IN BODY –INTERACTS WITHX-RAY PHOTONFROM TUBE
17 Compton scatterA fairly high energy (high kVp) x-ray photon ejects an outer shell electron.Though the x-ray photon is deflected with somewhat reduced energy (modified scatter), it retains most of its original energy and exits the body as an energetic scattered photon.A Compton e- is also releasedSince the scattered photon exits the body, it does not pose a radiation hazard to the patient.It can, however, contribute to film fog and pose a radiation hazard to personnel (as in fluoroscopic procedures).
20 Compton scatterBoth the scattered x-ray and the Compton electron have enough energy to cause more ionization before loosing all their energyIn the end the scattered photon is absorbed photoelectrically
21 Compton EffectThe Compton electron looses all of its kinetic energy by ionization and excitation and drops into a vacancy in an electron shell previously created by some other ionizing eventThe probability of Compton effect increases as photon energy increases, however the atomic number does not affect the chances of the Compton effect
22 Compton ScatterCompton is just as likely to occur with soft tissue as bone. Compton can occur with any given photon in any tissueCompton is very important in Radiography, but not in a good way.Scattered photons provides no useful diagnostic information
23 Compton EffectScattered radiation produces a uniform optical density on the radiograph that reduces image contrastScattered radiation from Compton contributes to the majority of technologists exposure, especially during fluoroscopySTAY AWAY FROM YOUR PATIENT !
24 Photoelectric Effect or Absorption Inner-shell ionizationThe photon is not scattered it is totally absorbedThe e- removed from the atom of matter is called a photoelectron, with an energy level equal to the difference between the incident photon and the e- binding energy.
27 PHOTOELECTRIC ABSORBTION IN THE PATIENT(CASCADE OF ELECTRONS)
28 Photoelectric effectA relatively low energy (low kVp) x-ray photon uses all its energy (true absorption) to eject an inner shell electron,leaving an orbital vacancy.An electron from the shell above drops down to fill the vacancy and, in doing so, gives up energy in the form of a characteristic ray.The photoelectric effect is more likely to occur in absorbers of high atomic number (eg, bone, positive contrast media)and contributes significantly to patient dose,as all the photon energy is absorbed by the patient (and for the latter reason, is responsible for the production of short-scale contrast).
29 Electron transitionsAre accompanied by the emission of more x-rays – secondary radiationSecondary radiation behaves much like scatter radiationSecondary contributes nothing to the imageThe probability that any given photon will undergo a photoelectric interaction is dependent on the photon energy and the atomic number of the atom
33 Important X-ray Interactions Of the five interactions only two are important to radiologyPhotoelectric effect or photoelectric absorptionCompton scatter
34 Compton scatter Contributes to no useful information Is independent of the atomic number of tissue. The probability of Compton is the same for bone atoms and for soft tissue atomsThe probability for Compton is more dependent on kVp or x-ray energy
35 Compton ScatterResults in image fog by optical densities not representing diagnostic informationPhoton are PhotonsIR is does not knowthe difference
36 Photoelectric Absorption Provides information to the IR because photons do not reach the IRThis represents anatomic structures with high x-ray absorption characteristics; radiopaque structures; tissue with high atomic number; or tissue with high mass density
37 Attenuation – The total reduction in the # of photons remaining in an x-ray beam after penetration through tissueAbsorption = x-ray disappears (Photoelectric, Pair production & Photodisintegration)Scattering = partially absorbed, x-ray emerges from the interaction traveling in a different direction (sometimes with less energy)Absorption + Scattering = Attenuation
39 3 Types of x-rays are important for IMAGE FORMATION DIFFERENTIAL ABSORPTION = the difference between those x-rays absorbed and those transmitted to the IRCompton scatter (no useful information)Photoelectric absorption (produces the light areas on the image)Transmitted x-rays (produces the grey/dark areas on the image)
40 Differential Absorption Increases as the kVp is reducedApproximately 1% of photons that interact with the patient (primary beam) reach the IR. Of that 1% approximately 0.5% interact to form the image
41 Differential Absorption The difference in x-ray interactionsFundamental for image formationOccurs because of Compton Scattering, Photoelectric absorption, and X-ray transmission
43 Compton vs. Photoelectric Below 80 kVp Photoelectric absorption is predominant above 80 kVp Compton scatter begins to increase.Dependent on the tissue attenuation properties
44 Differential absorption factors High atomic number = larger atomsMass Density = how tightly the atoms of tissue are packedZ # for air and soft tissue are about the same the OD changes are due to mass density difference
45 Human BiologyX-rays are harmful, low energy photons can cause skin burns, cancer, leukemiaIt is not known for certain the degree of effect following diagnostic levels of x-radiation
46 Technologists Responsibilities Technologists, Student Technologists, Radiologists & Medical Physicists have ethical & professional responsibilities to produce high-quality x-ray images with minimal radiation exposureWhat is the acronym for this?
51 Natural radiationNatural radiation accounts for approximately 300 millirem (mrem)3 sources of environmental radiation: cosmic rays, terrestrial radiation and internally deposited radionuclides. The largest source of natural radiation is radon.
53 Biological Response to Ionizing Radiation X-ray interactions with matter (human tissue) can cause biological changes.Technologists must understand cellular biology and how radiation interacts with cells in order to protect oneself and the patient.RBE – Relative Biological Effectiveness
59 RadiobiologyThe study of the effects of ionizing radiation on biologic tissueMost radiobiology research is designed to develop dose-response relationships to determine the effect of planned doses or accidents
63 Rad VS. Rem 1 RAD X QF = 1 REM 1 GRAY X QF = 1 SIEVERT QF FOR X-RAYS = 1So…… Rads = Rems
64 TYPES OF RADIATON (ALL CAUSE IONIZATION) ELECTROMAGNETICXRAYGAMMA(damaged caused by indirect action = free radicals – can be repaired)PARTICULATEALPHABETAFAST NEUTRONSUnit of mesaure is the curie (Ci) or becquerel (Bq)More destructive
65 QUALITY FACTOR Qualifies what the damage is from different types of radiationExample: QF for X-ray is 1QF for alpha is 20Alpha is 20 x more damaging to tissue
66 Measures biologic tissue response to radiation Measurement(Rad + QF = Rem)RBE-Measures biologic tissue response to radiation
69 Patient doseIs reported in Entrance Skin Exposure (ESE)
70 REGULATORY AGENCIESNCRP – National Council on Radiation Protection and Measurement ?NRC – Nuclear Regulatory Committee ?Other regulatory agencies?
71 REGULATORY AGENCIESNCRP – National Council on Radiation Protection and MeasurementReviews recommendation for radiation protection & safetyNRC – Nuclear Regulatory CommitteeMakes LAWS & enforces regulationsCalifornia Department of Public Health, Radiologic Health Branch (CDPH) Title 17
72 Human Radiation Response The effects of x-rays on human is the result of interactions at the atomic levelIonization or excitationThe result if a deposit if energy in tissue. The excess energy can result in a molecular change that can be measurable if the molecule involved is critical to metabolic function
74 Atom ionizationCan cause chemical binding property change. If the atom is part of a large molecule the ionization may cause molecule break down or relocation of the atom within the molecule
75 Abnormal moleculesIn time may function improperly or cease to function. This may cause serious impairment or death of the cellThis process is reversible by the ionized atom attracting a free e- and become neutral againCell and tissues can regenerate and recover from the radiation injury
76 Cell bombarded with photons What damage will they cause?
77 TARGET THEORYBIOLOGIC RESPONSE TO IONIZING RADIATION DEPENTS ON WHERE THE PHOTON INTERACTSCELL STRUCTURENUCLEUS & CYTOPLASMThe most at risk area of the cell…….CHROMOSOMES, WHICH ARE MADE UP OF GENES.
78 Cellular Absorption Direct vs. Indirect Hit Direct Hit Theory:When radiation interacts with DNA.Ionization of a DNA molecule.Break in the bases or phosphate bondsCan injure or kill the cellIndirect Hit Theory:Occurs when water molecules are ionizedProduces chemical changes – injury or cell deathVast majority of cellular damage is from indirect hit.
79 CellsThe most radiosensitive part of the cell is the deoxyribonucleic acid (DNA)Water is the most abundant molecule in the body. The body is 80% water. Humans are basically made of structure water.
80 Basic Cell Structure Two parts: 1. Nucleus 2. Cytoplasm Nucleus contains chromosomes – genetic info (DNA)DNA is at risk when a cell is exposed to ionizing radiationCytoplasm – 80% water
81 Tissue response to radiation A precise knowledge of various organ radiosensitivities in unnecessary. However, it is important to have a general knowledge of effects of radiation exposureA few important general principals are important to understand
82 Response of cells to radiation CELL SENSITIVITY TO RADIATIONTYPE OF CELLAGE OF CELLTYPE OF DAMAGE RECEIVEDKIND OF RADIATION EXPOSURE
83 Human cell typesTwo general types:Somatic cellsGenetic cells
84 MOST CONCERNING EFFECTS OF RADIATION EXPOSURE LATE EFFECTSSOMATIC EFFECTS = INDIVIDUAL EXPOSEDGENETIC EFFECTS =FUTURE GENERATIONS
89 Radiolysis poison water theory The human body is 80% water molecules and 1% DNA moleculesIrradiation of water represents the principal radiation interaction in the bodyWhen water is irradiation, it dissociates into other molecular products – RADIOLYSIS OF WATER
90 Formation if ions & free radicals The ion pair may rejoin into a stable water moleculeIn this case, no damage is done
94 Radiosensitivity of Cells Bergonie & Tribondeau (1906) – method of classifying a cell’s response to radiation according to sensitivity.Cells are most sensitive during active division (primitive in structure & function).
95 Cells that are most sensitive to radiation Young – immature cells The Law of Bergonie & TribondeauxCells that are most sensitive to radiationYoung – immature cellsStem CellsHighly dividing (mitotic) cellsHighly metabolic
97 Early vs Late effects of Radiation Early Effect = response that occurs within minutes or days after exposureLate Effects = response that occurs within months or years**most human responses have been observed after LARGE doses. To be cautious we assume even small doses are harmful**
100 RadiobiologyIrradiated tissue response, besides the cell properties, is determined by the amount of energy deposited per unit massLinear Energy Transfer (LET) = the rate at which energy is transferred from ionizing radiation to tissue
101 LETThe ability of ionizing radiation to produce biologic response increases as the LET of radiation increasesWhen the LET of radiation increases ionizations increase. When LET is high, ionizations occur frequently, increasing the potential for biologic damage
102 Relative Biologic Effectiveness As the LET of radiation increases, the chances of biologic damage also increasesRelative Biologic Effectiveness (RBE) = standardizes biologic effects of radiation exposureRBE for diagnostic x-rays is 1radiation with lower LET is less than 1, radiation with higher LET is greater than 1
103 QUALITY FACTOR Qualifies what the damage is from different types of radiationExample: QF for X-ray is 1QF for alpha is 20Alpha is 20 x more damaging to tissue
104 TYPES OF RADIATON (ALL CAUSE IONIZATION) PARTICULATE(HIGH LET)ALPHABETAFAST NEUTRONSMore destructiveELECTROMAGNETIC(LOW LET)XRAYGAMMA(damaged caused by indirect action = free radicals – can be repaired)
105 Why did the bunny die?? BUNNY A Received 200 rads BUNNY B
106 Why did the bunny die?? BUNNY A 200 rads x 1 for X-RAY = 200 RADS BUNNY B200 rads x 20 for alpha =4000 rads
108 Biologic Factors Affecting Radiosensitivity Oxygen Effect – tissue is more sensitive when the tissue is oxygenatedAge – Humans are most sensitive before birth, sensitivity decreases until maturity, after maturity humans are mostly resistant to radiation effects
114 Radiation Dose-Response Relationships Every radiation dose-response relationship has two characteristicsLinear or NonlinearThreshold or Stochastic (chance)
115 Linear Dose-Response Relationships Linear dose-response – when radiation dose is doubled the response to radiation is likewise doubledNonthreshold dose-response – any dose, regardless of it size is expected to produce a response – chanceThreshold dose-response – a radiation doses below a certain level no response is expected
119 SOMATIC & GENETIC STOCHASTIC VS NON STOCHASTIC A = STOCHASTIC“CHANCE” EFFECTSNONTHRESHOLDGENETIC, LEUKEMIA, CANCERDIAGNOSTIC RADIOLOGYB= NON-STOCHASTICTHRESHOLD EFFECTSDETERMINISTICSOMATIC EFFECTSSKIN ERYTHEMA, CATARACTS, STERILITYRAD -MALIGNANCIES
120 Linear vs Non linearLinear – direct response to the dose and the effects seen (proportionally)Non linear – effects are not proportional to the dose receivedS curve – rad therapy, skin erythema, most somatic, deterministic radiation effects.
121 Organ SystemsAre identified by their rate of cell proliferation and their stage of development. Each organ system have different ratesImmature cells are called undifferentiated cells, precursor cells or stem cells.Stem cells are more sensitive to radiation than mature cells
122 Tissue typesRadiosensitivity of tissue is also dependent on structural or functional featuresTissue types include: Epithelium, Connective (supporting tissues), Muscle and NervousThe various organs of the body exhibit a wide range of sensitivity to radiation. This is determined by the function of the organ, the rate at which cells mature in the organ, and the inherent radiosensitivity of the cell type
127 Total Body Response to Radiation Acute Radiation Syndrome – full body exposure given in a few minutes.3 stages of response:1. Prodromal Stage: NVD stage (nausea, vomiting, diarrhea)2. Latent Period: Feels well while undergoing biological changes3. Manifest Stage: Full effects felt, leads to recovery or death
128 3 Acute Radiation Syndromes Early Effects Bone marrow syndrome: results in infection, hemorrhage & anemiaGastrointestinal syndrome: results in diarrhea, nausea & vomiting, feverCentral nervous syndrome: results in convulsions, coma, & eventual death from increased intracranial pressure.CNS least sensitive in ADULTS –MOST sensitive in the FETUS
129 Late Effects of Radiation Somatic Effects: develop in the individual who is exposedMost common: Cataract formation & CarcinogenesisGenetic Effects: develop in future generations as a result of damage to germ cells.
130 SENSITIVITY TO RADIAITION Which (Male or Female) GONADs are external vs internalWhich gender is born with all their reproductive cells?Which gender constantly produces new cells?Which GENDER is more sensitive to radiation at birth? Why?
135 Permissible Occupational Dose Annual dose:5 Rem / year 50 mSv / year (NOT TO EXCEED 1.25 rem/quarter)Cumulative Dose1rem x age 10mSv X age
136 OCCUPATIONAL EXPOSURES 5 REMS / YEARBUT NOT TO EXCEED 1.25 REM/QUARTERTechnologist essentially receive all exposure during fluoroscopy exams
137 Occupational Dose ANNUAL LIMITS WHOLE BODY = 5 rems / 5000mremLENS OF THE EYE = 15 remsEXTREMITIES = 50 rems
138 PUBLIC EXPOSURE 10 % OF OCCUPATIONAL NON MEDICAL EXPOSURE (MUST BE MONITORED IF ABOVE 10%)NON MEDICAL EXPOSURE.5 RAD OR 500 MRADUNDER AGE 18 AND STUDENT100 mrem mSv
139 GSD 0. 20 mSv or 20 millirem GENETICALY SIGNIFICANT DOSE Takes all of the population into accountAnnual AVERAGE gonadal dose to population of childbearing age0. 20 mSv or 20 millirem*Bushong*30 mrem per NRC website
140 Fetus ExposureRadiation exposure is most harmful during the first trimester of pregnancyEmbryo-Fetus Exposure limit (Monthly)0.05 rem or 0.5 mSv
142 Effects of radiation in utero are time and dose related Effects include:Prenatal death, neonatal death, congenital abnormalities, malignancy inductions, general impairments of growth, genetic effects, and mental retardation.
143 Irradiation in UteroThe first trimester is the most radiosensitive period. After the 2 weeks of fertilizationThe first 2 weeks of pregnancy may be of least concern because the response is all or nothing
148 Pregnant patient ALWAYS ASK LMP before exposure made “10-day Rule” No longer used“Grace period” of implantationWhat is the State Law for gonadal shielding?
149 Pregnant PatientsShould never knowingly expose a pregnant patient unless a documented decision to so has been madeIf you must expose; use precise collimation & protective shields. Use a high kVp technique and only the minimal projections
150 Unsuspected pregnancy Always screen female patients for last LMPdon’t assume ages (patient privacy)If unsure obtain a blood test or reschedule exam if possible
151 PREGNANT PATIENTS Ascertain LMP - if fetus is exposed Medical Physicist will need information:Which x-ray machine used (mR/mAs)# Of projections (including repeats)Technique for each exposureSIDPatient measurement at C/RFluoro time & technique usedPhysicist will calculate fetal dose
152 90 % of cell damage will repair. At each stage cell repair is possible
153 Protraction & Fractionation cause less biological effect If radiation is delivered over a long period of time rather than quickly, the effect of that dose is lessened. Allows for intercellular repair and tissue recovery.ProtractionDose is delivered continuously but at a lower dose rateFractionationSame dose rate in short doses over a longer period (occupational exposure)
154 Biologic Factors Affecting Radiosensitivity Recovery – human cells can recover from radiation damage. If the radiation dose is not sufficient to kill the cell before its next division. Then given sufficient time, the cell will recoverIf a tissue or organ receives a sufficient radiation dose it responds by shrinking or atrophy. Cells disintegrate and are carried away as waste products
155 Hormesis Pg. 518 repair that can occur when below 5 rads of exposure A growing body of radiobiologic evidence suggests that a little bit of radiation is good for you. It stimulates hormonal and immune responses to other toxic environmental agentsWe still practice ALARA
156 Why cancer risks at low doses are uncertain It has been difficult to estimate cancer induction risks, because most of the radiation exposures that humans receive are very close to background levels.At low dose levels of millirems to tens of rems, the risk of radiation-induced cancers is so low,that if the risk exists, it is not readily distinguishable from normal levels of cancer occurrence.In addition, leukemia or solid tumors induced by radiation are indistinguishable from those that result from other causes.