Radiation Terminology

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Radiation Terminology

• Presented By
• Vivian Heep, RHIT, CTR
• Cancer Registry Manager
• Moncrief Cancer Center
• September 29, 2005

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What is radiation therapy?

• Energy is delivered to the body to destroy
  aberrant cells.
• The energy is created with electric or nuclear
  sources.
• Energy form can be
• External beam
• Implants
• Isotopes
• Combination of modalities

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What is radiation therapy? (cont)

• Radiation damages cells so that they die when
  they divide.
• Malignant cells divide more rapidly than normal
  cells.
• The goal of radiation therapy is to deliver
  enough energy to kill malignant cells but not the
  normal cells.

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What is radiation therapy? (cont)

• How it works
• External beam is photons and/or electrons
• Weak energy (low power) penetrates shallow
• Strong energy (high power) penetrates deeper
• Electrons penetrate shallowly
• Photons penetrate deeply
• Longer exposure times equal higher doses

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What is radiation therapy? (cont)

• There is a maximum amount of life-time radiation
  that any given body tissue can tolerate.
• Once this maximum is reached, or closely
  approached, no more radiation can be given to
  that tissue.
• The maximum is organ/tissue-, histology-, and
  age-specific.

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Common Radiation Terms

• Radiation Oncologists
• Physicians who specialize in treating
  malignancies with radiation therapy
• Counsel patients
• Make treatment decisions
• Write prescriptions
• Supervise treatment
• Follow the patient to determine the outcome of
  the treatment

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Common Radiation Terms (cont)

• Physicists
• Ph.D or Masters Degree in physics
• Specially trained people
• Energy and machine specialists
• Take the prescription and create a treatment plan
• Capable of planning for every patient

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Common Radiation Terms (cont)

• Dosimetrists
• Specially trained people
• Bachelors degree
• Can enter the profession through on-the-job
  training by advancing from Radiation Therapist
  positions
• Create treatment plans for routine cases
• Assists Physicists with difficult treatment plans

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Common Radiation Terms (cont)

• Radiation Therapists
• Specially trained people who deliver the
  treatment to the patients
• Operate the equipment (computers and linear
  accelerators)
• Ensure that
• Correct daily dose is delivered
• Patient is properly positioned
• Patient is as comfortable as possible

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Common Radiation Terms (cont)

• Linear Accelerator (Linac)
• Most common type of delivery system
• Special equipment that creates radiation using
  high voltage electricity
• C-shaped arm rotates around the patient to
  achieve the optimum position
• The arm has a head with the aperture (opening)
  through which the radiation is beamed

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Common Radiation Terms (cont)

• Simulator
• A machine configured exactly as a linac but which
  does not create radiation.
• Used to confirm the proper beam configuration and
  the patients planned position
• Confirms that the patient can maintain the
  required position for treatment

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Common Radiation Terms (cont)

• Blocks
• Special metal blocks attached to the outside of a
  linac head
• Custom designed to prevent unwanted radiation
• Prevent normal tissues from receiving radiation

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Common Radiation Terms (cont)

• Collimators
• IMRT technology
• Blocks unwanted radiation using two series of
  metal leaves positioned inside a linac head, one
  set on each side
• Usually 60 leaves per side
• Each is independently controlled by the computer
• Allows greater dose specificity and provides
  better protection for normal tissues

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Common Radiation Terms (cont)

• Aquaplast Mask
• Special mesh
• After wetting, it is shaped to fit the patients
  head and neck
• As it dries, it hardens but retains that shape
• After it has hardened, it is attached to a collar
  which can be attached to the treatment table
• Ensures that the patient is immobilized and is in
  the exact same position for each treatment
• Can be used for other areas of the body

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Common Radiation Terms (cont)

• Consult
• An informational meeting between a radiation
  oncologist and a patient to discuss radiation
  treatment options.
• Radiation vs. Surgery vs. Chemo vs. Hormone vs.
  combination
• Treat vs. no treatment
• Beam vs. Implant vs. Isotope vs. combination

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Common Radiation Terms (cont)

• Simulation
• The CT scans which are made of the patients body
  area to be treated
• Used to create the patients treatment plan

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Common Radiation Terms (cont)

• Treatment Plan
• The physicians prescription and the simulation
  are used to design the treatment plan.
• Describes the specific energies, times, linear
  accelerator positions and patient positions
  needed to deliver the prescribed radiation dose.

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Common Radiation Terms (cont)

• Dose
• The amount of radiation that is delivered to the
  patient.
• The optimum dose to achieve the maximum tumor
  effect is prescribed by the radiation oncologist.

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Common Radiation Terms (cont)

• Centigray (cGy)
• The unit of measure that describes the amount of
  energy that is given to the patient.
• 100 centigray equals 1 Gray
• Sometimes called rads

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Common Radiation Terms (cont)

• Volume
• The area of the body that receives radiation
  therapy.
• The volume can be one or more of
• Primary Site
• Draining lymphatics
• Metastatic site
• Surgical bed

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Common Radiation Terms (cont)

• Index Volume
• The volume that precipitates the patients
  radiation treatment.
• Ex A symptomatic brain met, from an asymptomatic
  lung primary, caused the patient to seek
  treatment. Both volumes are treated, but the
  Index Volume is the brain.
• This volume is captured in the FORDS data field

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Common Radiation Terms (cont)

• Laterality (of volume)
• The side of the body of the volume that is
  treated.
• Use the ACoS Paired site determination
• One exception is lymph nodes
• Do not confuse this with the direction that
  treatment is delivered.

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Common Radiation Terms (cont)

• External Beam
• Radiation from an external source (usually a
  linear accelerator linac)
• Photons
• Electrons
• Orthovoltage
• Cobalt

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Common Radiation Terms (cont)

• Photons
• Energy that is beamed into the body which is
  neutral (it does not have any electrical charge).
• Penetrates deeply into the body because it is
  neutral and passes through positive body tissues.
• Sometimes referred to as particles.

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Common Radiation Terms (cont)

• Electrons
• Energy that is beamed into the body which has a
  negative electrical charge.
• Penetration is shallow because the negatively
  charged electrons bind to positive molecules in
  the body.
• Sometimes referred to as particles.

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Common Radiation Terms (cont)

• Intensity Modulated Radiation Therapy (IMRT)
• Requires a linear accelerator with multileaf
  collimaters.
• External beam that is delivered using dynamic
  technology the linac arm moves around the body
  while the radiation is ongoing and the
  collimaters move so that changing doses are
  delivered to the target volume.
• Highly conformal treatment is delivered to the
  target volume rather than homogenous treatment to
  a large volume. (ex prostate instead of the
  entire pelvis)
• Allows more precise targeting of the tumor.
• Limits the amount of radiation delivered to
  surrounding normal tissue

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Common Radiation Terms (cont)

• Tomotherapy
• IMRT radiation that is delivered in a linear
  accelerator that also creates CT scans.
• When the patient is in treatment position before
  every treatment, a CT scan of the volume is
  performed.
• This facilitates confirmation that the tumor is
  appropriately targeted.
• Body and tumor tissues shrink and change positions

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Common Radiation Terms (cont)

• Brachytherapy
• The radiation source is placed inside or very
  near the target volume.
• Delivered with two intensities.
• Low Dose Rate (LDR)
• High Dose Rate (HDR)

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Common Radiation Terms (cont)

• High Dose Rate (HDR) Brachytherapy
• Nuclear source is usually Iridium 192
• Half-life of 74 days
• Requires minutes to achieve the target dose

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Common Radiation Terms (cont)

• Low Dose Rate (LDR) Brachytherapy
• Intracavitary source is usually Cesium 137
• Requires multiple hours to achieve the target
  dose
• Interstitial source is usually Pallidium
• Permanent implantation
• Both have a half-life of 30 years

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Common Radiation Terms (cont)

• Half-life
• The amount of time required for a nuclear
  radiation source to emit half of its radiation.
• The shorter the half-life, the more radiation is
  emitted and the less time is required to reach
  the target dose.

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Common Radiation Terms (cont)

• Implant
• Radiation is delivered to the patient using an
  internal (inside the body) source.
• Two types
• Interstitial implant
• Intracavitary implant

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Common Radiation Terms (cont)

• Interstitial Implant
• A radiation source (usually in the form of seeds
  or ribbons) is permanently implanted into the
  tissue of the target volume.

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Common Radiation Terms (cont)

• Intracavitary Implant
• A radiation source is placed into an application
  device
• The application device is placed inside a body
  cavity
• The device is removed when sufficient time has
  passed to deliver the prescribed dose

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Common Radiation Terms (cont)

• Isotope
• Dorlands definition A chemical element having
  the same atomic number (same of protons) as
  another but possessing a different atomic mass
  (different of neutrons). A radioisotope has an
  unstable nucleus (composed of protons neutrons)
  which gives it the property of decay by one or
  more of several processes.
• A radioactive isotope is administered either
  orally or intravenously
• Carried through the body by the vascular system
• Malignant tissues take up more than normal
  tissues
• Isotopes do not harm normal tissues because their
  half-life is short, normal tissue does not absorb
  it as quickly, and it is quickly biologically
  excreted

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Common Radiation Terms (cont)

• Fraction
• One treatment (of many) to a volume
• Each fraction is a specified portion of the total
  dose
• Fractions doses are cumulative
• Their total equals the total dose delivered to
  the patient

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Common Radiation Terms (cont)

• Regional dose
• The dose delivered to the volumes largest
  treatment field
• Usually the most cGys
• Usually delivered before a boost dose.

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Common Radiation Terms (cont) Anterior View of
A Regional Volume/Dose
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Common Radiation Terms (cont) Lateral View of A
Regional Volume/Dose
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Common Radiation Terms (cont)

• Boost Dose
• The dose delivered to a second, smaller volume
• This volume is inside the area of the regional
  volume/dose
• There will be fewer cGys given
• There may be several boosts that are sequentially
  smaller
• Almost always given after the regional dose is
  complete

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Common Radiation Terms (cont) A Boost
Volume/Dose
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Common Radiation Terms (cont) Regional and
Boost Volumes/Doses
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Common Radiation Terms (cont)

• Modality
• This describes the type and strength of the
  energy that is delivered during treatment
• There may be multiple strengths and/or energies
  in any given treatment
• Photons (6 Mv 18 Mv)
• Electrons (6e 12e)
• Implants
• Isotopes
• Combinations (Mv e Mv/e Implant/Isotope)

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Common Radiation Terms (cont)

• Mixed Strengths
• Almost always applies to external beam
• Multiple (usually two) strengths of the same
  energy are used to achieve the target dose

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Common Radiation Terms (cont)

• Mixed Energies
• Almost always applies to external beam
• Both photons and electrons are used to achieve
  the target dose
• Photons penetrate deeply
• Electrons penetrate shallowly

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Acknowledgements

• Moncrief Cancer Center
• David Hammond, Physicist
• Bridget Bong, CTR

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Vivian Heep, RHIT, CTRMoncrief Cancer
Center1450 Eighth AveFort Worth TX 76104(817)
927-6336Vivian.Heep_at_moncrief.com