PhD Thesis Defense: Rachael Hachadorian

For info on how to attend this videoconference, email rachael.l.hachadorian.TH@dartmouth.edu

"Towards Absolute Dosimetry and Field Verification of Whole Breast Radiation Therapy Treatment Using Cherenkov Imaging"

Abstract

This thesis focused on the development of a fundamentally new way to validate the precision and accuracy of radiation therapy treatment sessions (predominantly in breast patients) by optically imaging the Cherenkov light emitted during delivery.

Specifically, the utility of Cherenkov imaging has been explored in the largest patient cohort known, and a thorough feasibility assessment was completed to determine what steps are necessary for Cherenkov light to become a viable reporter for both the consistency of the beam shape and delivered surface dose on the patient. The techniques involved applying whole-image and point-by-point correction factors to account for optical attenuation and distortion of the Cherenkov intensities due to patient-specific and treatment-specific differences, which usually arise from light absorption due to interior blood volumes, tissue types and skin pigmentations. These differences skew the light intensity-to-dose linearity and misreport the delivered surface dose. This work determined the level of accuracy that can be achieved by correcting for patient tissue optical differences, beam energy, and beam-to-patient geometries within these fields. With continued development, Cherenkov images may then become direct, video-rate maps of the delivered surface dose with sufficient positional and dosimetric accuracy to be used in clinical monitoring. Specific studies examined correction methods that utilize SFDI, optical reflectance, and x-ray CT tissue composition. One of the more promising approaches showed through a series of controlled phantom imaging and analysis of patient imaging studies, that a systematic calibrations can be introduced to correct for many of these dominant parameters, based upon the tissue radio density, or CT number. Further refinement can correct for inter-patient and inter-fraction superficial skin changes.

Additionally, beam shape imaging serves as an important aspect of this work, which allowed for the quantification of patient position accuracy for both single- and multi-field irradiation. In multi-field imaging, the resulting match line accuracy could be verified using Cherenkov images. All patient data was collected directly in imaging sessions at both of Dartmouth-Hitchcock Health’s Lebanon and Cheshire Medical Centers. In summary, this work was able to (1) demonstrate quantitative evidence that Cherenkov imaging can estimate field edges to clinical accuracy, and (2) determine how to develop this imaging modality to achieve quantitative remote dose imaging in whole breast radiotherapy.

Thesis Committee

• Brian Pogue, PhD (Chair)
• David Gladstone, ScD
• Petr Bruza, PhD
• Lesley Jarvis, MD, PhD
• Rongxiao Zhang, PhD
• Michael Jermyn PhD
• Todd Pawlicki PhD

Contact

For more information, contact Daryl Laware at daryl.a.laware@dartmouth.edu.