X-rays, being a type of electromagnetic radiation, interact with the atoms and molecules of human tissues as they pass through the body. Linear Energy Transfer (LET) is a fundamental concept in the study of radiation biology and the effects of ionizing radiation on living tissues.

1. Transmission of X-ray through
body tissues linear energy
transfer
Presenter: Dr. Dheeraj Kumar
MRIT, Ph.D. (Radiology and Imaging)
Assistant Professor
Medical Radiology and Imaging Technology
School of Health Sciences, CSJM University, Kanpur
05 March 2024
Transmission of X-ray through body tissues linear energy
transfer By- Dr. Dheeraj Kumar
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2. X-ray Transmission Through Body Tissues
• X-rays, being a type of electromagnetic
radiation, interact with the atoms and
molecules of human tissues as they pass
through the body.
• The interaction processes primarily involve
absorption and scattering, which determine
the extent of X-ray transmission through
different types of tissues.
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Transmission of X-ray through body tissues linear energy
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3. Absorption
• Absorption refers to the process where X-ray photons are absorbed by the
atoms within the tissue.
• The extent of absorption depends on the energy of the X-ray photons and the
atomic composition of the tissue.
• Higher atomic number elements (e.g., calcium in bones) tend to absorb more X-
rays compared to lower atomic number elements (e.g., carbon in soft tissues).
• Consequently, tissues with higher density and higher atomic number elements
absorb more X-rays, leading to reduced transmission through those tissues. For
example, bones absorb a significant portion of X-rays, resulting in decreased
transmission and producing radiographic shadows on X-ray images.
• In medical imaging, the absorption characteristics of different tissues helps in
the interpretation of radiographic images and the detection of abnormalities.
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Transmission of X-ray through body tissues linear energy
transfer By- Dr. Dheeraj Kumar
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4. Scattering
• Scattering occurs when X-ray photons interact with the electrons of atoms in the tissue,
causing them to change direction.
• There are several types of scattering, including the Compton effect and coherent
scattering.
• Compton scattering involves the collision of an X-ray photon with an outer-shell electron,
resulting in the ejection of the electron and a scattered X-ray photon with reduced energy.
• Coherent scattering, also known as Rayleigh scattering, involves the elastic scattering of
X-ray photons by the whole atom without any loss of energy.
• Scattering contributes to the overall attenuation of the X-ray beam as it passes through the
tissue, reducing the intensity of the transmitted beam.
• While scattering can degrade image quality by producing scattered radiation that may blur
the image, it also provides valuable information about tissue composition and density.
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Transmission of X-ray through body tissues linear energy
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5. Importance of Linear Energy Transfer (LET)
• Linear Energy Transfer (LET) is a
fundamental concept in the study of
radiation biology and the effects of
ionizing radiation on living tissues.
• It provides crucial insights into how
radiation deposits energy as it traverses
through biological matter, influencing the
biological response to radiation exposure.
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Transmission of X-ray through body tissues linear energy
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6. Definition of Linear Energy Transfer (LET)
• Linear Energy Transfer (LET) refers to the average
amount of energy deposited by ionizing radiation
per unit length of tissue along its path.
• It is expressed in units of kiloelectronvolts per
micrometer (keV/μm) or megaelectronvolts per
meter (MeV/m).
• LET characterizes the density of energy deposition
along the radiation track and is influenced by the
type and energy of the radiation.
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Transmission of X-ray through body tissues linear energy
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7. Comparison with Other Types of Radiation
• Different types of ionizing radiation, such as X-
rays, gamma rays, alpha particles, and beta
particles, exhibit varying LET values.
• High-LET radiation deposits a significant
amount of energy over a short distance,
resulting in dense ionization along its path.
• Low-LET radiation, such as X-rays and gamma
rays, deposits energy more sparsely along its
path due to interactions with atomic electrons,
resulting in a lower density of ionization.
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Transmission of X-ray through body tissues linear energy
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8. Biological Effects of LET
• The biological effects of ionizing radiation depend not only
on the total absorbed dose but also on the LET of the
radiation.
• High-LET radiation, such as alpha particles and heavy ions, is
more effective in producing complex DNA damage, including
double-strand breaks, which can be difficult for cells to repair.
• Low-LET radiation, such as X-rays, primarily induces single-
strand breaks and other simpler forms of DNA damage.
• The effectiveness of radiation in causing biological damage
increases with increasing LET, as high-LET radiation deposits
more energy per unit length of tissue, resulting in greater
damage to cells and tissues.
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Transmission of X-ray through body tissues linear energy
transfer By- Dr. Dheeraj Kumar
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9. Clinical Implications
• Understanding the concept of LET is essential in
radiation therapy for optimizing treatment strategies
and selecting appropriate radiation modalities.
• High-LET radiation modalities, such as proton therapy
and heavy-ion therapy, offer advantages in targeting
radioresistant tumors and minimizing damage to
surrounding healthy tissues.
• In diagnostic radiology, the low-LET nature of X-rays
is advantageous for producing diagnostic images with
minimal biological effects on patients.
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Transmission of X-ray through body tissues linear energy
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10. Interaction Mechanisms
The mechanisms by which X-rays
interact with body tissues is essential
for comprehending their effects and
optimizing medical applications. X-
rays primarily interact with tissue
atoms through three main processes:
the photoelectric effect, Compton
scattering, and coherent scattering.
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Transmission of X-ray through body tissues linear energy
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11. Coherent Scattering
• Coherent scattering, also known as Rayleigh scattering, involves the
interaction of an X-ray photon with the entire atom.
• The incident photon interacts with the electron cloud of the atom, causing it
to oscillate momentarily before re-emitting the photon in a different direction
with the same energy.
• Coherent scattering is prevalent at low X-ray energies and contributes
minimally to tissue absorption.
• While coherent scattering does not significantly contribute to image
formation, it provides valuable information about tissue composition.
• Example: In mammography, where tissue differentiation is critical, coherent
scattering may contribute to the formation of subtle image details that aid in
the detection of abnormalities in breast tissue.
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Transmission of X-ray through body tissues linear energy
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12. Photoelectric Effect
• In the photoelectric effect, an incident X-ray photon interacts with an inner-shell
electron of an atom.
• The energy of the X-ray photon is absorbed by the electron, causing it to be ejected
from the atom.
• The atom then becomes ionized, and the excess energy is transferred to the ejected
electron, known as a photoelectron.
• This process is more likely to occur with atoms containing electrons with binding
energies close to the energy of the incident X-ray photon.
• The photoelectric effect dominates at lower X-ray energies and contributes
significantly to tissue absorption.
• Example: In bone imaging, where high-density tissues are predominant, the
photoelectric effect plays a crucial role in attenuating the X-ray beam, resulting in
radiographic contrast between bone and surrounding soft tissues.
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Transmission of X-ray through body tissues linear energy
transfer By- Dr. Dheeraj Kumar
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13. Compton Scattering
• Compton scattering involves the interaction of an X-ray photon with a loosely
bound outer-shell electron of an atom.
• The incident photon transfers a portion of its energy to the electron, causing it to
be ejected from the atom with reduced energy.
• The scattered photon, with decreased energy and altered direction, continues its
path through the tissue.
• Unlike the photoelectric effect, Compton scattering is not strongly influenced by
the atomic number of the tissue.
• Compton scattering becomes more prevalent at higher X-ray energies and
contributes to the overall attenuation of the X-ray beam.
• Example: In diagnostic radiography, where X-ray energies are typically higher,
Compton scattering is a primary contributor to the formation of scattered radiation
that may degrade image contrast and quality.
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Transmission of X-ray through body tissues linear energy
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14. Biological Effects of X-ray Radiation
• X-ray radiation, while invaluable in medical imaging and therapy, can
exert various biological effects on human tissues.
• These effects range from immediate cellular damage to long-term
health consequences and are influenced by factors such as radiation
dose, dose rate, and tissue sensitivity.
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Transmission of X-ray through body tissues linear energy
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15. DNA Damage and Cellular Effects
• X-ray radiation can directly ionize atoms within biological molecules, including
DNA, leading to the formation of DNA strand breaks, base damage, and cross-
links.
• Indirectly, X-rays can generate reactive oxygen species (ROS) within cells,
causing oxidative stress and further DNA damage.
• The accumulation of DNA lesions can disrupt cellular processes, including DNA
replication and repair, ultimately leading to cell death or mutation.
• Example: Single-strand breaks induced by low-LET X-rays may be efficiently
repaired by cellular mechanisms, while complex DNA damage caused by high-
LET radiation can be more challenging to repair, potentially resulting in
permanent genetic alterations or cell death.
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Transmission of X-ray through body tissues linear energy
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16. Tissue Responses and Biological Effects
• The biological effects of X-ray radiation depend on the sensitivity of
different tissues and organs to radiation-induced damage.
• Highly proliferative tissues, such as bone marrow and gastrointestinal
epithelium, are more sensitive to radiation due to their rapid cell
turnover rates.
• Chronic exposure to low doses of X-rays may increase the risk of cancer
development, particularly in radiosensitive tissues.
• Conversely, acute exposure to high doses of X-rays can cause
deterministic effects, such as radiation burns and radiation sickness.
• Example: In radiation therapy, the goal is to deliver a therapeutic dose
of radiation to tumor tissues while minimizing exposure to adjacent
healthy tissues, thereby reducing the risk of long-term side effects.
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Transmission of X-ray through body tissues linear energy
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17. Radiation Carcinogenesis and Long-Term Risks
• Prolonged or repeated exposure to X-ray radiation, particularly at high
doses, can increase the risk of cancer development through the
induction of genetic mutations and chromosomal abnormalities.
• The latency period between radiation exposure and the manifestation of
radiation-induced cancers can range from several years to decades.
• The carcinogenic potential of X-ray radiation depends on factors such
as dose, dose rate, and individual susceptibility.
• Example: Epidemiological studies have linked occupational exposure to
X-rays, such as in radiology and nuclear medicine, with an increased
risk of certain cancers, highlighting the importance of radiation
protection measures in minimizing occupational hazards.
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Transmission of X-ray through body tissues linear energy
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18. Clinical Applications
• X-ray radiation finds extensive use in clinical practice across various
medical specialties, owing to its ability to penetrate tissues and
produce detailed images. Additionally, X-rays play a crucial role in
therapeutic interventions, particularly in radiation oncology. Clinical
applications of X-ray radiation is essential for optimizing patient care
and treatment outcomes.
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Transmission of X-ray through body tissues linear energy
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19. Diagnostic Imaging
Radiography: It started when Wilhelm Conrad Roentgen discovered X-
rays in 1895
Fluoroscopy: It was invented by Thomas Edison in 1896, shortly after the
discovery of X-rays by Wilhelm Roentgen in 1895
Computed Tomography(CT): The first clinical CT scan of the human brain was
performed in 1971 using a scanner invented by Sir Godfrey Hounsfield, who
shared the Nobel Prize in Physiology or Medicine in 1979 with Allan McLeod
Cormack for the development of computerized
Mammography: The first mammography study was performed by German
surgeon Albert Salomon in 1913, on 3,000 mastectomies.
Interventional: Interventional radiology was conceived on Jan. 16, 1964, when
Charles Dotter, MD, percutaneously dilated a stenosed segment of the superficial
femoral artery in an 82-year-old woman with gangrenous ischemia who refused
leg amputation.
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Transmission of X-ray through body tissues linear energy
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20. Radiation Therapy
• X-ray radiation is a cornerstone of radiation therapy, employed in the treatment of various cancers through the
delivery of precisely targeted radiation doses to tumor tissues.
• External beam radiation therapy (EBRT) utilizes linear accelerators to deliver high-energy X-ray beams to the
tumor while sparing adjacent healthy tissues.
• Intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) optimize the
delivery of radiation by modulating beam intensity and shaping the radiation dose to conform to the tumor's
shape.
• Brachytherapy involves the placement of radioactive sources directly within or adjacent to the tumor site,
allowing for localized delivery of high-dose radiation while minimizing exposure to surrounding tissues.
• X-ray radiation therapy aims to eradicate cancer cells, shrink tumors, and alleviate symptoms, offering curative
or palliative treatment options depending on the disease stage and patient's condition.
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22. Radiation Safety and Quality Assurance
• In both diagnostic and therapeutic applications, ensuring radiation safety and quality assurance is
paramount to minimize patient dose and optimize imaging and treatment outcomes.
• Radiation protection measures, including lead shielding, collimation, and dose monitoring, are
implemented to reduce unnecessary radiation exposure to patients, healthcare providers, and the
public.
• Quality assurance programs, such as regular equipment calibration, dose verification, and
personnel training, uphold the highest standards of radiation safety and ensure the accuracy and
efficacy of X-ray procedures.
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Transmission of X-ray through body tissues linear energy
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23. Radiation Protection
• Radiation protection is paramount in medical settings where X-ray radiation is
utilized for diagnostic imaging and therapeutic interventions.
• Effective radiation protection measures aim to minimize radiation exposure to
patients, healthcare workers, and the general public while ensuring the delivery of
high-quality healthcare services.
• This slide explores various aspects of radiation protection and their importance in
maintaining safety and quality in radiology and medical physics practices.
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Transmission of X-ray through body tissues linear energy
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24. Patient Protection
• Patient protection strategies focus on minimizing radiation dose while obtaining diagnostic information
necessary for clinical decision-making.
• Optimization of imaging protocols involves selecting appropriate exposure factors, such as X-ray beam
energy, tube current, and exposure time, to achieve diagnostic image quality with the lowest possible radiation
dose.
• Use of shielding devices, such as lead aprons and thyroid collars, helps reduce unnecessary radiation exposure
to sensitive organs and tissues during X-ray procedures.
• Education and informed consent empower patients to make informed decisions about their healthcare and
understand the benefits and risks associated with X-ray examinations.
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Transmission of X-ray through body tissues linear energy
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25. Occupational Safety
• Occupational safety measures aim to protect healthcare workers involved in the delivery of X-ray services
from unnecessary radiation exposure.
• Use of personal protective equipment (PPE), including lead aprons, thyroid shields, and radiation badges,
helps minimize radiation exposure to radiographers, radiologists, and other personnel working in radiology
departments.
• Implementation of radiation safety protocols, such as time, distance, and shielding, ensures that healthcare
workers maintain safe distances from radiation sources and limit exposure time during X-ray procedures.
• Regular training and education on radiation safety practices, including radiation physics, dose management,
and emergency procedures, are essential for promoting a culture of safety and compliance among healthcare
staff.
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26. References
• "Radiation Biology for Medical Physicists" by E. J. Hall
• "Radiobiology for the Radiologist" by Eric J. Hall and Amato J. Giaccia
• "Essentials of Radiologic Science" by Robert F. Christ, Denise L. Orth, and Thomas S.
Curry
• "Principles of Radiographic Imaging: An Art and A Science" by Richard R. Carlton and
Arlene M. Adler
• "Radiation Protection in Medical Radiography" by Mary Alice Statkiewicz Sherer, Paula
J. Visconti, and E. Russell Ritenour
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