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External Beam Radiotherapy (EBRT)

Chamal Kohombakadawala

MSc. (UOC), BSc. (Hons) in Eng, CTHE (KDU)

Department of Electrical Electronics and Telecommunication Engineering

Newspaper Article

Daily Mirror

  • Radioactive sources

  • For treatments

  • Terminology – Radiotherapy / Radiation Therapy

What is this about

Radiotherapy

(Radiation Therapy)

Radiotherapy

  • Clinical process
  • Ionizing radiation
  • (High energy X-ray or gamma rays)
  • Treatment purposes
  • Tumors

AIM

AIM

  • Deliver a very accurate dose of radiation

  • Well defined target volume

  • Minimum damage to surrounding healthy tissues

Improve quality of life !!

TYPES

  • External beam radiotherapy (teletherapy).

  • Brachytherapy (sealed source radiotherapy)

  • Unsealed source radiotherapy

  • Particle/ion beam radiotherapy

External Beam Radiotherapy

  • Source located outside

  • Use high energy beams
  • Gamma rays / X-rays

  • Beams directed using machines

EBRT

60Co Radiotherapy

Machine

Cobalt 60

Machines

Details

  • Natural source
  • Gamma rays
  • Energies of 1.173 and 1.332 MeV
  • Activity 5000–10000 Ci
  • Half-life - 5.27 years

  • Drawbacks
  • High surface dose
  • No MLC – localization issues
  • Always leakage radiation

Skin Dose

Typical values for 10 × 10 cm2 field

  • Cobalt-60 beam - 30% of the maximum dose
  • 6 MV x-ray beam - 15%
  • 18 MV x-ray beam - 10%

Linear Accelerators

(LINACs)

LINACs

LINACs

About

  • Linearly accelerate
  • Electrons
  • High energies (6MeV, 9MeV)

Standard method of producing photons and electrons

  • High frequency electromagnetic waves used
  • Produced by Magnetron or Klystron

Acceleration Process

Block Diagram

Define the Beam

MLC

  • Multiple blocks/leaves
  • Driven automatically, independent to each other
  • Generate field of any shape
  • 1 cm or less made of tungsten alloy

Beam Types

  • Clinical photon (x-ray) beams:
  • Appropriate x-ray target.
  • Appropriate flattening filter

  • Clinical electron beams
  • Scattering foils (pencil beam to broad beam)
  • Electron applicators

Photon

Vs.

Electron Beams

Treatment Planning

Assignment

Test Your Understanding

Kahoot Quiz (3 questions – 10s each)

Discuss

  • Magnetron Vs. klystron
  • LINACs Vs. 60Co machines
  • Disposal methods of 60Co source

(Due on next Monday)

Summary

  • Radiotherapy / Radiation Therapy
  • External Beam Radiation Therapy (EBRT)
  • Linear Accelerators (LINACs)
  • 60Co machines
  • Next Week – Treatment planning and dose calculations

References

  • LINAC (Linear Accelerator). [online] Radiologyinfo.org. Available at: <https://www.radiologyinfo.org/en/info.cfm?pg=linac> [Accessed 7 March 2021].
  • Gibbons, J. and Khan, F., n.d. Khan's The Physics of radiation therapy.
  • Wright, A., 1992. Medical physics handbook of radiation therapy. Madison, Wis.: Medical Physics Pub.
  • Sciencedirect.com. 2021. Linear Accelerators - an overview | ScienceDirect Topics. [online] Available at: <https://www.sciencedirect.com/topics/physics-and-astronomy/linear-accelerators> [Accessed 7 March 2021].
  • Moffitt Cancer Center. 2021. Linear Accelerator (LINAC). [online] Available at: <https://moffitt.org/treatments/radiation-therapy/linear-accelerator-linac/> [Accessed 7 March 2021].
  • Pubs.rsna.org. 2021. The Stanford Medical Linear Accelerator | Radiology. [online] Available at: <https://pubs.rsna.org/doi/10.1148/72.2.242> [Accessed 7 March 2021].

Thank You!!

Thank You!

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