Introduction to Physics, Biology, and Safety Review 2024 PDF

OD 522 Course Intro, Physics, Biology and Safety Review Department of Oral and Maxillofacial Radiology, Boston University Course schedule ATTENDANCE IS MANDATORY! The final grade for this course will be determined by the following: Examination 1 25% Examination 2 25% Final Examination 45% Quizzes an...

OD 522 Course Intro, Physics, Biology and Safety Review Department of Oral and Maxillofacial Radiology, Boston University Course schedule ATTENDANCE IS MANDATORY! The final grade for this course will be determined by the following: Examination 1 25% Examination 2 25% Final Examination 45% Quizzes and Assignments 5% The following distribution represents the letter grades given for final grades: 93% & above-A 90-92% - A87-89% - B+ 83-86% - B 80-82% - B- 77-79% - C+ 73-76% - C 70-72% - C60-69% - D bone than soft tissue Create “fog” on the images Photoelectric Absorption Most interactions take place in the K-shell: electron density is highest here Characteristic x-ray formation Approximately 30% of all interactions X-ray photon strikes an electron near the nucleus with enough energy to knock it off its orbit; overcomes its binding energy. Photon is totally absorbed and its energy transferred to the ejected /recoil electron. Beam Attenuation Reduction in the intensity of x-ray beam as it traverses matter by either absorption or deflection of photons from the beam Measured using the half value layer (HVL): HVL is defined as the thickness of any material required to reduce the intensity of the beam in half. Beam Hardening: mean energy of beam is increased HALF VALUE LAYER A MEASURE OF ATTENUATION HVL Intensity 100 % Intensity 50 % Factors affecting attenuation: Energy of radiation, atomic number (Z) of material through which it passes, tissue density, electron density etc. DIFFERENTIAL ATTENUATION ▪ Different body parts attenuate the x-ray beam to different extents depending on their density, thickness, energy of the beam, beam size etc. ▪ Image contrast. Dosimetry Exposure Ability of X-rays or gamma rays to ionize air, measured as a charge per mass of air The traditional unit was the roentgen (R), which was described as: 1 R =2.58 x 10 C/kg Measures the intensity of the radiation field Roentgen replaced by the SI equivalent of air kerma Air Kerma Kerma = kinetic energy released in matter Measure of the energy transferred from photons to electrons Gray (Gy) 1 Gy = 1 J/kg Dose Quantities Absorbed Dose Absorbed dose (D ) is the amount of total energy absorbed by a unit mass of matter SI unit (Gy). 1 Gy = 1 J/kg The traditional unit was the rad (radiation absorbed dose) 1 Gy = 100 rad Equivalent Dose Comparing the biologic effects of different radiation types on organs and tissues Particulate radiation (e.g. protons, gamma rays, neutrons, alpha particles, etc.) have a higher linear energy transfer (LET) than ionizing radiation of lower energy (e.g. X-rays) This difference is called radiation-weighting factor (WR) Unit is the sievert (Sv), 1 Sv = 1 Gy. The traditional unit was rem (roentgen equivalent man), 1 Sv = 100 rem Effective Dose Calculate the risk to humans Measured by tissue weighting factors WT ICRP 2007 WT red bone marrow, breast, colon, lung, and stomach 0.12 gonads 0.08 bladder, esophagus, liver, and thyroid 0.04 bone surface, brain, salivary glands, and skin 0.01 other tissues totaling 0.12 Unit of the effective dose is the sievert (Sv) Radiobiology It is a medical science that involves the study of biological effects of ionizing radiation on living tissues Sources of Radiation Background Space Terrestrial Man made CT, CBCT, PET, Fluro… Radiation Chemistry Initial interaction of radiation and matter occurs at 10 -13 seconds after the exposure Direct Effects: immediate effects caused by ionizing radiation on macromolecules Indirect Effect: ionizing a water molecules causing free radical formation in turn interacts with biological molecule The 1st recorded biologic effect of radiation was described by Becquerel with skin erythema due to radium. Followed by ulceration that appeared 2 weeks later. Healing process took several weeks. Peirre Curie repeated this experience in 1901 deliberately producing a radium burn on his own forearm. Direct Effect Biologic molecules absorb energy from ionizing radiation and form unstable free radicals. Free radicals: extremely reactive and short lived 1/3 of the biologic effects of x-‐ray exposure result from direct effects Changes in DNA Breaking one or both of the DNA strands. Change or loss of a base Cross-‐linking a strand of DNA to other areas within the helix or to other strands Disruption of hydrogen bonds between DNA strands Indirect Effect Human body has approximately 70% water. X-‐ray + H2O -‐> H. + OH. Radiolysis of water -‐ hydrogen and hydroxyl free radicals About 2/3 of the biological damage by x-‐rays is caused by indirect action Stochastic and Deterministic (non-stochastic effects) Stochastic effects: Do not have a threshold for expression. ex. Cancer, mutations, genetic defects. Non-stochastic effects: Demonstrate a threshold for expression. Effect is directly proportional to the radiation dose/dose rate. ex. skin erythema, cataract, whole body radiation syndromes etc. Effects of Radiation Deterministic Effects Radiation injury to organisms results from either the killing of large numbers of cells DNA damage Cell death Decrease in tissue and organ function Examples Xerostomia Stochastic Effects Sublethal damage to individual cells that results in cancer formation or heritable mutation Sub-‐lethal DNA damage Gene mutation Replication of mutated cell Examples Osteoradionecrosis Leukemia Cataracts Salivary gland tumor Thyroid cancer Heritable disorders Effects on Oral Tissues The radiotherapy course continues for 6 to 7 weeks untill a total of 60 to 70 Gy. 2 Gy is delivered daily for a weekly exposure of 10 Gy (deterministic effects) Oral Mucous Membrane Taste Buds Salivary Glands Teeth Bone Decision to Use Radiodiagnostic Procedures Osteoradionecrosis Pathologic fx’s secondary to ORN Radiation Caries A 36-year-old female with tongue cancer who underwent postoperative chemoradiotherapy. The radiation field included the lower jaw but not the upper jaw. Multiple dental caries occurred, mainly in the mandibular teeth. A: Panoramic X-ray before RT. B: Two years after RT. C: Six years after RT. DOI: 10.15761/OHC.100012 1 Radiotherapy may produce short roots Radiation Safety & Protection Reducing Dental Exposure Justification Optimization ALARA Principle (As Low As Reasonably Achievable) Dose limitation Reduce Dental Exposure Justification Optimization ALARA Principle ( As low As Reasonably Achievable ) Dose Limitation Thank you !