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Head, Division of Radiation Oncology , University of Western Ontario
Director, Physics Research and Education , London Regional Cancer Program
Tel: 519-685-8600 x53613
Radiation dose computations, radiation detection in 3D, new radiation sources for brachytherapy, radiobiology of DNA damage and repair.
Three-Dimensional Dose Mapping (with K. Jordan, K. Chu, B. Rutt)
Recent technological advances are making it possible to improve X-ray treatments using three-dimensional (3D) irradiation techniques available in our London Regional Cancer Program (LRCC). Verification of 3D dose distributions is essential before they can be used clinically on patients. A new dosimetry technique has been developed in our lab for the measurement of such dose distributions produced in tissue-equivalent gel absorbers. The chemical dosimeter is composed of ferrous sulphate, benzoic acid, and xylenol orange (FBX), mixed with a gel substrate. We map the local changes in optical density due to radiation energy absorption using a green Helium-Neon laser scanning through the gel (in two dimensions) to produce dose images, slice by slice, using optical computed tomography. We can also measure this dose distribution using magnetic resonance imaging (MRI) which yield T1 relaxation maps in the same gel material for direct comparison.
Tomotherapy (with J. VanDyk and G. Bauman)
Tomotherapy, literally translated, means slice therapy. Tomotherapy is an evolving technology that employs slit-like radiation beams. These beams have the same shape as the beam that is used for diagnosis in CT scanning. However, there are two main differences. First, the beam has a high energy (6 MV versus 120 kV). Second, as the beam rotates about the patient, a series of radiation absorbing vanes are inserted into the beam dynamically. These are used to control the beam intensity along the length of the slit. These vanes move in and out as the beam rotates around the patient and reduce the dose to normal tissues as needed. The patient moves into the gantry aperture while the beam is on and while the absorbing vanes move in and out so that the path "spirals" around the patient. On the exit side of the patient is a set of radiation detectors, which are used to generate a CT scan of the patient. Thus tomotherapy is a machine that provides both the capabilities of tumour and normal tissue localization while the patient is in the treatment position, as well as very sophisticated radiation treatment and verification - all in one machine. We hope to have one of the first machines installed at the LRCC for prototype evaluation, unique radiobiology studies, and early clinical trials.
New Radiation Sources for Brachytherapy (with P. Munro)
Brachytherapy is the placement of small radiation sources within or near the tumour bed using guide needles. Radioactive sources have been used in the past and, for example, we were the first to use Ytterbium-169 clinically (October 1990). We continue to evaluate new commercial seeds such as the new generation of Iodine-125 seeds. However, radioactive sources have the limitations of emitting discrete photon energies, decaying dose rate, and of radiation protection. It would therefore be advantageous to have a miniature X-ray needle with variable energy and with a "on/off" switch, as is now being developed commercially. Our lab will evaluate such new technology, performing X-ray spectroscopy and 3D dosimetry with the long-term goal of brain or prostate cancer treatments.
Optimal X-rays for DNA Damage in Tumour Cells (with E. Yu and P. Truong)
Radiosensitizing drugs, such as Iodinated deoxyUridine (IUdR), can be used in combination with X-rays to enhance the killing of tumour cells. IUdR substitutes for thymidine in the DNA structure of rapidly-dividing cells and the Iodine serves to absorb X-rays with a photon energy near 33 keV. By using this optimal excitation energy, we can accentuate the radiation damage as measured by cell survival and of DNA fragmentation. By using the "comet assay" for DNA damage, it may be also possible to measure the radiosensitivity of tumours in individual patients before deciding on their treatment strategy and dose prescription. Initial DNA damage and the enzymatic repair rate can also be measured.