Author ORCID Identifier
https://orcid.org/0000-0003-4215-318X
Date of Award
Spring 5-2026
Document Type
Thesis (Ph.D.)
Department or Program
Engineering Sciences
First Advisor
Petr Bruza
Abstract
Radiation therapy (RT) is a widely adopted cancer treatment technique, contributing to over 50% of all cancer treatments worldwide while improving quality of life for many others. Effective RT relies on rigorous quality assurance, including routine treatment plan validation and verification of machine output. However, variations in patient setup and anatomical changes over the course of treatment can cause deviations from the prescribed plan, potentially compromising treatment efficacy or increasing treatment related morbidity. Verification and monitoring of dose delivery could address these issues but is currently limited to point measurements using in-vivo dosimeters (IVDs) which offer limited utility in large treatment fields or areas of high dose gradients, and provide little to no temporal information. Furthermore, recent advancements in the pursuit of more effective treatment techniques have shown that ultra-high dose rate (UHDR) radiation delivery introduces predominantly healthy tissue sparing, termed the FLASH effect, but repeatability was shown to be sensitive to dose and dose rate dynamics, the verification of which requires wide area monitoring capabilities that current IVD cannot provide. The limitations of existing IVD systems therefore affects both conventional therapy and UHDR applications, where precise spatiotemporal dose characterization is critical, underscoring the need for comprehensive, full‑field treatment monitoring and dynamic surface dosimetry.
The first part of this thesis focuses on the development and application of a deformable scintillator array for high‑speed, wide‑area surface dosimetry across radiotherapy modalities. FLASH pencil beam scanning (PBS) proton therapy served as the driving application due to its increased spatial, temporal, and dosimetric complexities and the lack of available full field surface dosimetry in ongoing clinical trials. A prototype system was constructed and evaluated on an anthropomorphic phantom with spatiotemporally complex FLASH PBS plans to characterize performance and derive novel delivery verification metrics. Time resolved surface measurements were then used to develop a depth projection algorithm that estimated volumetric dose from surface dose dynamics. Translation of this dosimetry technique to conformal proton FLASH and conventional PBS is underway. The array was also adapted to conventional photon therapy to monitor surface dose across wide areas and field gradients, enabling estimation of contralateral breast dose in phantom studies and in-vivo clinical whole‑breast radiotherapy.
The second part of the thesis aims to expand the utility of imaging-based treatment monitoring by investigating the spectral response of optical emission during external beam radiotherapy. High energy particles traveling through tissue have been shown to result in Cherenkov emission from the patient surface, and in cases of rapid high dose delivery like UHDR proton therapy can also lead to additional forms of tissue luminescence. While previous work has shown the Cherenkov emission is correlated with dose deposition, known spectrally heterogeneous attenuators in the tissue such as blood and oxygenation disrupt this relationship before the emission can be imaged. This work leverages the differential attenuation of tissue constituents by spectrally separating the surface luminescence using static, sequential, and simultaneous spectral signal filtering across proton, electron, and photon modalities. For proton therapy, this work evaluates the feasibility of such optical monitoring in conventional and FLASH applications, and uses spectral information to investigate the origin of emission. In conventional electron and photon therapy, where the emission is known to be Cherenkov-based, spectral signal separation is used to monitor inter-fractional physiological development through changes in blood content and tissue oxygenation. Finally, by leveraging the known attenuation properties of the primary tissue constituents, the work offers a path to correct for local effects of hemoglobin signal attenuation in photon radiotherapy, bringing the technique of Cherenkov imaging closer towards relating collected surface emission to deposited surface dose.
Recommended Citation
Vasyltsiv, Roman, "Multimodal Optical Imaging for Dynamic Surface Dosimetry and Treatment Monitoring in Conventional and Ultra-High Dose Rate Radiotherapy" (2026). Dartmouth College Ph.D Dissertations. 497.
https://digitalcommons.dartmouth.edu/dissertations/497
