Abstract

To further develop a MV x-ray portal imaging device with high detection efficiency and adequate spatial resolution for image guided radiation therapy, the experimental results for a prototype detector were matched using Monte-Carlo software to then improve upon the design. The simulation and experiment were carried out using a 6 MV beam from a linear accelerator machine. An adequate match was obtained with the spatial resolution matching up to a MTF value of 0.2 and then diverging and the total signal registered in the central fiber was matched for field sizes ranging from 3 cm by 3 cm to 20 cm by 20 cm for 5 cm, 15 cm and 25 cm air gaps within 3%. The design was altered from a hexagonal array of round double cladded fibers to a square array of single cladded square fibers. The spatial resolution was improved from 0.242 lp mm-1 to 0.359 lp mm-1 at an MTF value of 0.5 from the original design to a square array of square fibers 0.5 mm wide separated by 0.25 mm of lead foil. With further optimization of the detector design it may be possible to increase spatial resolution for MV x-ray imaging while maintaining an adequate detection efficiency.

Highlights

  • In Canada nearly half of the population is expected to be diagnosed cancer in their lifetimes with a total of 1⁄4 of Canadian mortality as a result of this disease

  • A reasonable match was obtained between the simulation and the experimental results for spatial resolution and the total signal for various field sizes

  • After the match was obtained the detector design was changed from a hexagonal array of round fibers to a square array of square fibers

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Summary

Introduction

In Canada nearly half of the population is expected to be diagnosed cancer in their lifetimes with a total of 1⁄4 of Canadian mortality as a result of this disease. In most cases the resulting tumor is treated by either surgery, chemotherapy, radiation therapy or a combination of these treatment modalities. The most common treatment is external beam radiation therapy. External beam therapy is most commonly delivered using a linear accelerator (LINAC) seen in figure 1.1 [2]. External beam radiation therapy is useful for treating tumors in regions where surgery carries a high risk or in regions where the tumor is inoperable. The goal of radiation therapy is to kill the cancerous cells while sparing the healthy cells. The LINAC uses megavoltage (MV) x-rays to primarily damage cancer cells by taking advantage of their high radio-sensitivity compared to healthy cells [3]

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