Understanding Radiation Units

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 22 Answer True or False 1.The same amount of radiation falling on the person at level of breast, head or gonads will have the same biological effects. 2.Effective dose can be easily measured.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 33 Introduction Several quantities and units are used in the field of diagnostic radiology to measure and describe radiation dose. Dosimetry is the quantitative determination of radiation doses. Some can be measured directly while others can only be mathematically estimated.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 4 Hot Coffee – Energy contained in a sip Excess Temperature = 60 º - 37 = 23 º 1 sip= 3ml 3x 23= 69 calories

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 5 Radiation Dose Lethal Dose= 4Gy LD 50/60 = 4 Gy For man of 70 kg Energy absorbed = 4 x 70 = 280 J = 280/418= 67 calories = 1 sip Energy content of a sip of coffee if derived in the form of X- rays can be lethal X-rays

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 6 6 Dose of Radiation  Radiation energy absorbed by a body per unit mass.  Dosimetry is the quantitative determination of radiation doses.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 77 Basic Radiation Quantities Used to quantify a beam of X or γ-rays There are: Quantities to express total amount of radiation. Quantities to express radiation at a specific point Radiation at a specific point Photon fluence Absorbed dose Kerma Dose equivalent Total radiation Total photons Integral dose

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 8 Exposure (X) Exposure is a dosimetric quantity for measuring ionizing electromagnetic radiation (X-rays & Ɣ- rays), based on the ability of the radiation to produce ionization in air. Units: coulomb/kg (C/kg) or roentgen (R) 1 R = C/kg

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 9 EXPOSURE (X) It is the ability of a radiation beam to ionize air. It is measured in roentgens ( R), where 1 R of radiation exposure produces ions carrying 2.58 x C of charge per kg of dry air. The exposure is the charge Q in the air per unit mass m exposure = Q/m 1 R = 2.58 x C /kg The only information X can give is how much radiation is present. It does not say anything about whether all this ionization is absorbed by the material.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 10 KERMA KERMA (Kinetic Energy Released in a Material): Is the sum of the initial kinetic energies of all charged ionizing particles liberated by uncharged ionizing particles in a material of unit mass For medical imaging use, KERMA is usually expressed in air SI unit = joule per kilogram (J/kg) or gray (Gy) 1 J/kg = 1 Gy

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 11 Absorbed dose, D, is the amount of (E) energy imparted by ionizing radiation to matter per unit mass (m). D = E / m SI unit = joule per kg (J/kg) or gray (Gy). In diagnostic radiology, KERMA and D are equal. Absorbed dose: D Harold Gray

Absorbed Dose (D) One gray (Gy) is the amount of radiation (regardless of the type) that will deposit 1 J of energy in 1 kg of matter. An older unit for absorbed dose is the rad, an acronym for radiation absorbed dose(rad). One rad is the quantity of ionizing radiation that will deposit 0.01 J ( 100 ergs) of energy in 1 g of absorbing material. 1 gray = 100 rad. Radiation Protection in Paediatric Radiology L02. Understanding radiation units 12

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 13 Mean absorbed dose in a tissue or organ The mean absorbed dose in a tissue or organ D T is the energy deposited in the organ divided by the mass of that organ.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 14 Now things get a little more complicated !

Equivalent Dose The biological effects of radiation depends on the type of radiation. Equal dose of Alpha particles and Gamma radiation does not affect the tissue the same way. To account for the difference of the biological effects of radiation, we use the quantity equivalent dose. Equivalent Dose is the product of absorbed dose and the radiation weighting factor w R for the type of radiation use. Equivalent dose = absorbed dose x w R The SI unit of equivalent dose is sievert (Sv) An older unit for equivalent dose is the rem, short for roentgen equivalent man. 1 Sv = J/kg Radiation Protection in Paediatric Radiology L02. Understanding radiation units

Radiation Weighting Factors, w R Radiation typeRadiation weighting factor, w R Photons1 Electrons and muons1 Protons and charged pions2 Alpha particle, fission fragments, heavy ions 5 Neutrons,energy < 10keV > keV >100keV – 2MeV > 2-20 MeV > 20 MeV (Source: ICRP 103) Radiation Protection in Paediatric Radiology L02. Understanding radiation units

17 Radiation Quantities and Units Equivalent dose (Unit = sievert, Sv ) Compares the biological effects for different types of radiation, X-rays, Ɣ-rays, electrons, neutrons, protons, α-particles etc. For X-rays, Ɣ-rays, electrons : absorbed dose and equivalent dose have the same value Gy = Sv. Rolph Sievert

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 18 Summary Dosimetric quantities are useful to know the potential hazard from radiation and to determine radiation protection measures to be taken Physical quantities - Directly measurable Protection quantities - Defined for dose limitation purposes, but not directly measurable. Application specific quantities - Measurable in medical imaging. Diagnostic Refernce Levels

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 19 Answer True or False 1.The same amount of radiation falling on the person at level of breast, head or gonads will have same biological effects. 2.Effective dose can be easily measured. 3.Diagnostic reference levels are not applicable to paediatric radiology.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 20 Answer True or False 1. False -Different organs have different radio-sensitivity and tissue weighting factors. 2. False -It can be only calculated using different methods.

Example 1 A certain biological sample is given a dose of 7.50 rad from alpha particles. a. Calculate the absorbed dose in grays. b. Calculate the equivalent dose in sievert and rems. c. If the same dosage is delivered using fast neutrons with w R of 20, how much dosage in grays will be needed? Radiation Protection in Paediatric Radiology L02. Understanding radiation units 21

a rad ( 1 Gy/ 100 rad) = Gy b. eq.dose = absorbed dose x Wr = (0.0750) ( 5) = Sv eq.dose = 7.50 rad (5) = 37.5 rem c. Absorbed dose = eq.dose / Wr = Sv/20 = Gy Radiation Protection in Paediatric Radiology L02. Understanding radiation units 22

Solve: 1.How does the biological damage of 100 rad of beta particles compare with that of 100 rad of alpha particles? 2.A 75.0 mg tissue sample is irradiated. If it abbsorbs mJ of energy, what is the absorbed dose? 3.A person whose mass is 60.0 kg has been given a full-body exposure to a dose of 25.0 rad. How many joules of energy are deposited in the body? Radiation Protection in Paediatric Radiology L02. Understanding radiation units 23

Answer. 1. For beta: Eq.dose = absobed dose x Wr 100 rad (1) = 100 rem For alpha: Eq.dose = absobed dose x Wr 100 rad (5) =500 rem 2. Absorbed dose = E/ m = mJ / kg = 32 Gy 3. Convert rad to Gy : 25 rad = 1 Gy/ 100 rad = 0.25 Gy absorbed dose = E/m E = absorbed dose (m) = 0.25 Gy (60 kg) = 15 J Radiation Protection in Paediatric Radiology L02. Understanding radiation units 24

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 25 Mass Defect and Binding Energy

E = mc 2 Radiation Protection in Paediatric Radiology L02. Understanding radiation units 26 It tells of the huge amount of energy locked up in ordinary matter.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 27 Protons and neutrons make up the nucleus. The mass of the nucleus is equal to the combined masses of its protons and neutrons. Nuclear reaction can be analyzed in terms of the masses and energies of the nuclei and the particle before and after reaction. E = mc 2 is used in analyzing nuclear reaction.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 28  Nuclear masses are measured using an instrument called mass spectrometer.  The mass of the atoms is then compared against a standard which is in the case is C-12 and is expressed in atomic mass unit (amu). The mass of C-12 is equal to 12 amu.  1amu = x kg  When compared to C-12, the mass of hydrogen is equal to amu.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 29 Masses of the Proton, Neutron and Electron  Mass of proton, m p = amu  Mass of neutron, m n = amu  Mass of electron, m e = amu

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 30  How does the measured mass of hydrogen compare with its nuclear mass?  Compare the measured mass of the helium nucleus to the combined masses of all the two protons and two neutrons.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 31  Compare the measured mass of the helium nucleus to the combined masses of all the two protons and two neutrons. Sol.  m He = amu  2m p = amu x 2 = amu  2m n = amu x 2 = amu  2m p + 2m n = amu amu = amu  Note: The nuclear mass of the Helium atom is less than the total mass of its constituent parts.  The difference in mass is known as the mass defect, Δ m.  Δ m = amu – amu = amu

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 32 Mass seems to disappear when protons and neutrons combine to form a nucleus. Einstein’s principle of mass- energy equivalence says that the missing mass ( mass defect) is converted into energy. The energy equivalent of the mass defect is known as the binding energy (BE). From E = mc 2 BE = Δmc 2 The binding energy for helium can be calculated: BE He = Δmc 2 = ( amu) ( 3x10 8 m/s) 2

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 33 1 amu = 931 MeV For He,. BE He = ( amu) ( 931MeV/ amu) = 28.4 MeV 1 amu = 1.66 x kg 1eV = x J

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 34 Solve: 1. Calculate the binding energy of deuterium consists of one proton and one neutron. Its nuclear mass is amu. 2. Compute the binding energy of C-12 and compare it with the binding energy of C Calculate the disintegration energy of the reaction below. Given: m U-235 = amum Zr-94 = amu m Ce-140 = amun = amu

Nuclear Fission and Fusion The process by which a heavy nucleus split into medium-sized nuclei. It is induced by bombarding a heavy nucleus with neutrons. When two nuclei come very close to one another at very high temperature, the strong nuclear binding force predominates and allows the nuclei to fuse, releasing large amount of energy. Radiation Protection in Paediatric Radiology L02. Understanding radiation units 35

Calculate the energy involved in the reaction. Radiation Protection in Paediatric Radiology L02. Understanding radiation units 36,

(1) mass of the reactants  = = Total mass of reactants= (2) Mass of the products  = = = Total mass of products= Radiation Protection in Paediatric Radiology L02. Understanding radiation units 37

Total mass of reactants= amu Total mass of products= amu Δ mΔ m = amu amu Radiation Protection in Paediatric Radiology L02. Understanding radiation units 38

E = (0.222 ) (931 MeV/amu ) = 206 MeV Radiation Protection in Paediatric Radiology L02. Understanding radiation units 39

Assignment : Applications of Radioactivity and Nuclear Energy Enumerate applications of radioactivity and nuclear energy that you are aware of. Group 1-3 will present a report on the applications of radioactivity and nuclear energy to. G-1: Food and Agriculture G-2: Diagnosis and Therapy G-3: Radioactive Dating Radiation Protection in Paediatric Radiology L02. Understanding radiation units 40

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 41 Backscatter Factors (Water) HVLField size (cm x cm) mmAl10 x 1015 x 1520 x 2025 x 2530 x

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 42 If the KAP is calculated by the system, you must know if the user added filtration you use is included or not ! Kerma-Area Product: KAP

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 43 Kerma-Area Product: KAP It is always necessary to calibrate and to check the transmission chamber for the X-ray installation in use In some European countries, it is compulsory that new equipment is equipped with an integrated ionization transmission chamber or with automatic calculation methods

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 44 Dosimetric Quantities for CT Computed Tomography Dose Index (CTDI) CT air kerma index Dose-Length Product (DLP) Air kerma-length product

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 45 ICRU 74 / IAEA TRS 457 CT air kerma index Free-in-air (C k ) In phantom (C k,PMMA ) Air kerma length product (P KA )

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 46 Dosimetric Quantities for CT Principal dosimetric quantity in CT is CT air kerma index: where K(z) is air kerma along a line parallel to the axis of rotation of the scanner over a length of 100 mm. N = Number of detectors in multi-slice CT T = Individual detector dimension along z-dimension The product NT defines the nominal scan beam width/collimation for a given protocol.

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 47 Dosimetric Quantities for CT Weighted CT air kerma index, C W, combines values of C PMMA,100 measured at the centre and periphery of a standard CT dosimetry phantoms

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 48 Dosimetric Quantities for CT Pitch (IEC, 2003): T= Single detector dimension along z-axis in mm. N=Number of detectors used in a given scan protocol (N>1 for MDCT), N x T is total detector acquisition width or collimation I=table travel per rotation Radiographic, 2002, 22:949-62

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 49 Volume CTDI describes the average dose over the total volume scanned in sequential or helical sequence, taking into account gaps and overlaps of dose profiles (IEC, 2003): Average dose over x, y and z direction Protocol-specific information Dosimetric Quantities for CT

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 50 Dosimetric Quantities for CT Kerma-length product (P KL ): where L is scan length is limited by outer margins of the exposed scan range (irrespective to pitch) P KL for different sequences are additive if refer to the same type of phantom (head/body)

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 51 Maximum Skin Dose (MSD) Measurement/evaluation of MSD Point or area detectors Cumulative dose at IRP (interventional radiology point) Calculation from technical data Off line methods Area detectors: TLD array, slow films, radiochromic films From KAP and Cumulative dose measurement

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 52 Method for MSD Evaluation: Radiochromic Large Area Detector Example: Radiochromic films type Gafchromic XR R 14 ” x17 ” useful dose range: Gy minimal photon energy dependence ( keV) acquisition with a flatbed scanner:b/w image, bit/pixel or, measure of OD measurement with a reflection densitometer

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 53 Benefits of Radiochromic Films The radiochromic film: displays the maximum dose and its location shows how the total dose is distributed provides a quantitative record for patient files provides physician with guidance to enable safe planning of future fluoroscopically guided procedures improves fluoroscopic technique and patient safety possible rapid semi-quantitative evaluation Example of an exposed radiochromic film in a cardiac interventional procedure

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 54 Rapid Semi-Quantitative Evaluation: Example For each batch number (lot #) of gafchromic film a Comparison Tablet is provided In the reported example we easily can recognise that the darkness area of the film, corresponding to the skin area that has received the maximum local dose, has an Optical Density that correspond at about 4 Gy

Radiation Protection in Paediatric Radiology L02. Understanding radiation units 55 DRLs for Complex Procedures 3rd level “ Patient risk ” 2nd level “ Clinical protocol ” 1st level “ Equipment performance ” Dose rate and dose/image (BSS, CDRH, AAPM) Level 1 + No. images + fluoroscopy time Level 2 + DAP + Peak Skin Dose (MSD) Reference levels (indicative of the state of the practice): to help operators to conduct optimized procedures with reference to patient exposure For complex procedures reference levels should include: more parameters and, must take into account the complexity of the procedures. (European Dimond Consortium recommendations)