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Measurement of proton beam dose profiles using a sensitive scintillation screen observed with a CCD camera

University of British Columbia

The Proton Therapy Facility at TRIUMF has been in routine operation since 1995 using 70 MeV protons extracted from the 500 MeV H" cyclotron to treat ocular melanomas. The main rationale behind using proton therapy over conventional therapy is its improved conformity (i.e. manipulating the beam to deliver maximum dose to the tumour volume and minimum dose to the healthy surrounding tissue) and uniformity of dose delivery. Efforts have been made to develop a rapid method of measuring dose profiles using a sensitive scintillating screen observed by a CCD camera. The main advantage of this sort of dosimetry system is its ability to do near real-time observation and analysis of the proton beam; the system offers a practical and timesaving method of quality control. Conventional proton dosimetry methods, which consist of a miniature detector scanned in a water box, can be slow and impractical for some studies. Experiments have been carried out using beam energies and intensities well matched to clinical doses. A scintillating screen enclosed in a light tight box is placed in the path of the proton beam, and is observed by a CCD camera. The CCD camera, which views the screen through a 45-degree mirror has an integrating mode for increased sensitivity and a frame grabber for immediate viewing. Various commercial intensifying screens have been evaluated and one screen Rarex PFG (ZnCdS:Ag) has been found to be 17 times more sensitive than the more commonly used LANEX (Gd₂0₂S:Tb) screen. The system has demonstrated to be useful for rapid visualization of lateral dose distributions to look at collimator scattering, beam steering, raw Bragg peaks, and effect of wedges.

Thesis/Dissertation

application/pdf

2009-05-26

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http://hdl.handle.net/2429/8248

Physics

University of British Columbia

UBCV

DSpace