Development of Monte Carlo techniques for radiation transport simulations and application to radiotherapy physics and dosimetry

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Over 600,000 cancer patients a year are treated by radiation in North America. A critical aspect of each treatment is the accurate delivery of a known dose of radiation to the tumour. Thus clinical dosimetry, the determination of the radiation dose delivered to the tumour and elsewhere in the patient, plays a central role in these treatments. This research program involves two separate components of clinical dosimetry. One goal is to improve our ability to measure the radiation dose in a water tank with a high degree of accuracy since this calibrates the output of the source of radiation which may be an accelerator or a small radioactive seed. Another goal is to improve our ability to take a knowledge of that "reference dose", and calculate the dose distribution inside a real patient exposed to the same source of radiation. The central tool used in this research program is a suite of computer codes developed by the principal investigator and colleagues. These codes use what are called Monte Carlo techniques to model the passage of radiation through matter, including measuring devices and patients. This research is supported by a powerful cluster of computers funded by CFI. These computer codes are used to study how the instruments which measure radiation are working and recent breakthroughs mean practical and accurate corrections can be calculated for the first time, thereby improving clinical radiation measurement. The results show problems with current methods at the 1 to 5% level, but since the errors can affect hundreds of thousands of patients, the effects can be important. In another component of the research program, use will be made of another breakthrough to rapidly calculate the dose distributions around radioactive sources placed in the body to kill tumours. Sophisticated techniques have been developed to do accurate calculations of the very complex sources used, while the time taken for the calculations has been reduced from days to minutes. The goal now is to make the programs easier to use so that clinical physicists can make use of them on a routine basis and thereby improve cancer radiotherapy.