Radiation Therapy (RT) Basics



RT Advances


Photon (high energy X-rays) radiotherapy generated by linear accelerators is standard treatment. There have been technological advances in the past 10 to 20 years. All of these advances are designed to treat the tumor more accurately while sparing surrounding tissues.

Conformal radiotherapy:

  • Three dimensional conformal RT is is generally the current standard of care.
  • Photon beam is aimed from multiple angles with shielding.
  • Special collimators (movable shielding leaves) in machine head to provide accurate shielding.
  • This is described in the RT planning section.



  • This means implanting the tumor bed with radioactive sources and is another way of concentrating the dose in the tumor bed and limiting dose to surrounding structures. 
  • This is not a recent innovation, but techniques have evolved using "After-loading" - which means that catheters can be placed in the tumor bed and the radioactive seeds loaded afterwards. This makes the technique far safer for medical staff to use.
  • Problems with this technique include variations in the dose distribution if the treatment volume is too large, but this can be a very good way to treat smaller tumors and spare surrounding normal tissues.


IMRT (Intensity Modulated Radiotherapy)

  • Uses many more fields than 3D conformal RT.
  • Each field has a different, varying intensity profile.
  • In this way the high dose volume can be very carefully shaped around the tumor.
  • The technology for IMRT at the BC Cancer Agency is provided by Varian.
  • RapidArc is a new form of image-guided IMRT.
  • Link:


RapidArc Demo

Stereotactic Radiotherapy

  • Means of precisely treating tumors with linear accelerator based technology.
  • Treatment can either be given in one single fraction or in many fractions. 
  • The radiotherapy can be aimed precisely at the tumor within 2mm or so.
  • Link:

Brain Lab



  • CT Image-guided, intensity modulated radiation therapy.
  • Link:





  • Cyclotrons produce energetic charged particles - protons.
  • Have a similar radiobiologic effect to photons. 
  • Protons have a special Bragg peak curve and can deliver high dose treatment with a margin of only a mm or so. 
  • There is a proton beam which treats only eye tumors in Vancouver.  In Canada there is no proton facility to treat other tumor sites.  Presently we send pediatric patients to proton centers in the United States if this therapy is indicated.
  • Links:

The Francis H. Burr Proton Therapy Center at the Massachusetts General Hospital, Boston

Proton Therapy at Loma Linda University Medical Center

The Proton Therapy Center at The University of Texas M. D. Anderson Cancer Center

Gamma knife

  • Numerous independent Co60 sources concentrated on a single target. 
  • Gamma Knife delivers single doses of RT to targeted areas of the brain with a precision of less than 1 mm.
  • The beam is precise, but surrounding normal tissue does receive minimum scattered radiation.
  • There are gamma knife facilities in Winnipeg and Toronto.
  • Links:

Gamma Knife (Winnipeg)

Gamma Knife (Toronto)

Back to top