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[PAST EVENT] Physics Colloquium - Dr. Paul Black
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Dr. Paul Black, Wake Forest University, Title: Innovations in Surface Guidance Techniques for Radiotherapy Applications
Abstract:
About half of all cancer patients receive radiation therapy, which is delivered in a prescribed number of fractionated doses. As such, radiation therapy delivery requires accurate and repeatable patient positioning, ideally to sub-millimeter accuracy, for each fraction. This need for reproducible, consistent patient positioning becomes even more important as the plan complexity or the dose per fraction increases. Conventionally, patient positioning is verified before radiation delivery, but not actively monitored for changes during treatment. Positioning verification performed in real-time, concurrent with treatment, stands to improve on this methodology. Recently, groups have been working towards establishing methods for real-time verification of radiation treatment delivery. The two techniques presented use optical light to track patient positioning and verify radiation delivery.
When particles of sufficient energy travel through human tissue, light emission, known as Cherenkov radiation, is observable on the irradiated patient skin. This has been shown to correlate with ionizing radiation dose delivery in solid tissue, allowing real-time treatment verification. Cherenkov light images were acquired during radiation delivery to standard and anthropomorphic phantoms. Two clinical scenarios were tested: 1) observation of field overlaps or gaps in matched radiation fields and 2) patient positioning shifts during modulated dose delivery. The second technique investigated is Optical Surface Guidance (OSG), in which an optical light field is projected onto the patient surface and monitored using a multi-angle camera system. This technology can reliably monitor the patient surface in real-time, but cannot visualize radiation dose.
The detectability limit for determining radiation field placement and phantom position was investigated. For matched radiation fields, measurements of Cherenkov images agreed with known field separations. Detection of sub-millimeter positioning shifts was also demonstrated. For Cherenkov imaging, the major confounding factors were radiation angle of incidence, beam energy, and radiation type. For the OSG investigation, we verified sub-millimeter accuracy of the system, including rotational position changes. The combination of Cherenkov detection and OSG can be used in the development and refinement of a real-time patient and radiation delivery monitoring technique for clinical radiation dose delivery.