External Beam Radiotherapy (EBRT)
Chamal Kohombakadawala
MSc. (UOC), BSc. (Hons) in Eng, CTHE (KDU)
Department of Electrical Electronics and Telecommunication Engineering
- 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
- 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
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
- 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
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].