Mod 5

• Radiation


  Energy in transit or traveling through space
• Categories of radiation

  • Ionizing Radiation
  • Non-ionizing Radiation

  
• Non-ionizing radiation


  Radiation that does not have enough energy to ionize an atom
• Ionizing radiation


  Radiation that has enough energy to ionize an atom

  
• Types of ionizing radiation

  • Directly Ionizing
  • Indirectly Ionizing

  
• Indirectly ionizing radiation


  Particles that are uncharged or neutral that can ionize by a process or initiate an ionization process

  
• Indirectly ionizing radiation

  • Photons
  • Neutrons

  
• Directly ionizing radiation


  Particles that carry a charge and have sufficient kinetic energy to produce ionization by a direct collision

  
• Directly ionizing charged particles

  • Light Charged Particles (Electron, Beta Particle)
  • Heavy Charged Particles (Alpha Particle, Proton)

  
• In radiotherapy, high energy gamma rays are commonly used to treat cancer cells or control the growth rate of cancer cells

  
• Dose (Absorbed Dose)


  Energy deposited or absorbed in a small fixed weight of a material
• Dose unit

  Gray (Gy)
• Traditionally, the dose is measured in rad
• Dosimeter


  Device that measures dose uptake of external ionizing radiation

  
• Types of dosimeters

  • Thermoluminescence Dosimeter (TLD)
  • Ionization Chamber
  • Radiographic Film
• 1 Gray = 1 Joule/Kilogram
• Electron contamination


  Some gamma rays will interact with the internal components of the LINAC head and be emitted to the patient

  
• Dose determination process

  1. Determine the output of the machine

  2. Determine the absorbed dose in the irradiated medium

  
• Percentage Dose Distribution (PDD)


  Absorbed dose at a given depth expressed as a percentage of the absorbed dose at a reference depth on the central axis

  
• The PDD curve using a high energy photon shows the maximum dose (Dmax) is obtained at a certain depth within the patient body

  
• Gamma-ray is indirectly ionizing, meaning it doesn't directly ionize the atom inside the body but has a certain distance or depth where it gives out most of its energy and where electron equilibrium happens

  
• The PDD curve for heavy charged particles is very localized at the Bragg peak, requiring ultra precise patient positioning to avoid damaging nearby organs
• As the SSD (source-to-surface distance) increases


  The PDD (percentage dose distribution) increases
• The composition of the irradiated medium affects the penetration of the beam and the scattering characteristics, thus affecting the PDD curve
• The PDD curve has variations depending on the composition of the material being irradiated, with changes in relative dose at interfaces between materials of different densities
• As the beam energy increases

  The Dmax (maximum dose) moves deeper into the tissue and the skin-sparing effect increases
• Radiotherapy uses high-energy radiation to kill cancer cells and shrink tumors, which can be delivered externally (External Beam Radiation Therapy) or internally (Brachytherapy)
• Higher the beam energy

  Dmax moves to the left (deeper), and the skin-sparring effect increases
• PDD Curve with respect to different beam energy

  • 6 MV photons
  • 5 MV photons
• Comparing 6 MV photons and 5 MV photons

  Dmax moves to the left of the graph which then moves the depth of the Dmax within the phantom or tissue
• Changing the energy from 6 MV to 15 MV photons

  Ds or the dose on the surface decreases, Dmax moves to the left or in deeper within the phantom and the skin-sparring effect also increases
• TYPICAL VALUES OF SURFACE DOSE
• Radiotherapy or Radiation Therapy


  A type of cancer treatment that uses high-energy radiation to kill cancer cells and shrink tumors. The radiation can be delivered externally (EBRT) or internally through implants or radioactive substances (Brachytherapy)
• Radiotherapy


  • Can be used to treat many different types of cancer
  • The type and duration of radiotherapy treatment will depend on the type and stage of cancer being treated, as well as the patient's overall health and other individual factors
• Interaction of Radiation with Matter

  • Radiation kills cancer cells by damaging DNA
  • Protons are more lethal to cancer cells than x-rays
  • Carbon ions are 2-3 times more damaging than x-rays
• The radiation damages the DNA of the cancer cells, which prevents them from dividing and growing. While healthy cells can also be affected by the radiation, they are often able to repair themselves, whereas cancer cells are not. Radiotherapy can be used alone or in combination with other cancer treatments, such as chemotherapy or surgery.
• Fundamental Goal of Radiotherapy

  To deliver a dose of ionizing radiation to eradicate the cancer and, at the same time, limit the dose received by the surrounding healthy body tissue to as small as possible

  
• Current Status of Radiotherapy

  • Radiotherapy can be given with or without surgery and/or chemotherapy
  • Radical RT for tumor control, typically 30-40 treatments (fractions) up to 80 Gy
  • Adjuvant RT to control occult diseases after surgery
  • Neoadjuvant RT given before the main treatment
  • Palliative RT for symptom control, 1-5 fractions
• General Radiation Therapy Clinical Pathway

  1. Referral from the referring physician

  2. Initial Consultation with RO/ planning booking/ consent

  3. Simulation and or mold room

  4. Treatment planning (Individualized plan developed)

  5. Treatment course commences in fractions

  6. Treatment course delivered includes treatment review

  7. Treatment course finishes

  8. Follow-up consultation
• Simulation


  A mock-procedure of a patient procedure using a dedicated CT unit for RT. The patient is comfortably set-up and positioned in the exact way they will be treated, and tattoos or fiducial markers are made as reference marks.