Improving the Utility Of Cherenkov Imaging in the Radiotherapy Clinic

Abstract

More than half of all cancer patients in the United States undergo fractionated, daily radiation therapy as a component of treatment. While radiotherapy is widely regarded as life-saving, errors during delivery can be severe or even fatal, despite their rarity. These incidents may not be noticed immediately, because the treatment beam is not observed directly, and radiation-induced injuries take time to manifest by nature. It is in this context that the goal of the research presented here is to develop new Cherenkov imaging techniques to be used during radiotherapy for quality assurance testing, as well as patient treatment verification.

Cherenkov imaging allows for direct optical visualization of radiation dose deposition as ionizing beams pass through dielectric material via the Cherenkov Effect, by which fast-moving charged particles excite optical emission from media as they relax after rapid polarization. The number of Cherenkov photons produced is proportional to radiation dose delivered for a monoenergetic beam. However, the number of photons that can be detected is governed by efficiency in reaching the detector, which is influenced by variation in tissue optical properties in living subjects. This thesis first focuses on clinical patient imaging requirements, and techniques to improve the correlation between detected Cherenkov light intensity and metrics relating to delivered dose. Patients undergoing whole-breast radiotherapy (WBI), volumetric modulated arc therapy (VMAT), and total skin electron therapy (TSET) are discussed.

Quality assurance imaging is more straightforward, since the optical properties of the irradiated subject can be controlled. The remainder of this thesis employs water tanks and solid plastics to measure relative dose optically. These methods are adapted to accommodate atypical large field setups for TSET, as well as cutting edge clinical systems combining concurrent magnetic resonance imaging with radiotherapy delivery systems (cobalt-60 and linac based).