Abstract
The effectiveness of radiation therapy depends on treatment assessment and adaptation.
Cherenkov light emitted during treatment delivery has emerged as a promising
tool for monitoring molecular and external beam radiation therapy treatment delivery.
This thesis investigates the characteristics of Cherenkov light emitted during radiation
therapy and its potential for treatment assessment.
In molecular radiation therapy (MRT), limited control over the uptake and elimination
of the radioisotope can result in significant inter-patient variability in the dose absorbed
by the tissue, and there is a need for accurate patient-specific dosimetry. This thesis
employs Monte Carlo simulations based on patient CT data to investigate the spatial
and spectral characteristics of Cherenkov light emitted in tissue and emerging at the
patient surface during MRT of the thyroid. A novel approach to dosimetry is introduced
based on the relationship between the Cherenkov light intensity at the surface and the
dose deposited in tissue. The potential for such a Cherenkov light-based dosimetry
technique is evaluated across multiple patient anatomies and for varying tissue optical
parameters and radioisotope uptake by the tumour. To account for the patient-specific
light transport in the body, a patient-specific correction factor is introduced. This
substantially reduces the inter-patient variability in the linear relationship between the
dose absorbed by the treated tissue and the surface light, enabling the definition of a
calibration curve for MRT dosimetry based on surface light measurements. The potential
for Cherenkov light-based dosimetry in MRT is thus demonstrated, and guidance
for translating this approach to clinical practice is provided.
In external beam radiation therapy (EBRT), radiation delivery is well controlled. However,
the response to treatment depends on the tumour physiology, and functionalimage
guidance plays an important role in treatment assessment and adaptation. This
thesis addresses functional imaging using Cherenkov light emitted in the tissue during
radiation delivery. Specifically, the characteristics of Cherenkov light emitted during
EBRT of the larynx are explored, and its potential for probing the tumour is evaluated.
Monte Carlo simulations of treatment delivery for intensity-modulated radiation
therapy and volumetric-modulated arc therapy have been performed using clinical radiotherapy
and CT data to model dose deposition, Cherenkov light emission and transport,
and light emerging at the patient surface. It is found that near-infrared light
emerging at the patient surface originates sufficiently deep within tissue and could potentially
be used to probe the tumour. It is also found that surface light measurements
restricted to smaller areas containing the region where the light emitted in the tumour
emerges (which can be determined through simulations performed prior to treatment)
could enable probing the tumour while being easier to integrate with the radiotherapy
system. By characterising the spatial distribution of Cherenkov light emission and identifying
detection settings, information for developing image reconstruction algorithms
for Cherenkov light-based tomography is provided. By quantifying the surface light,
this study indicates the level of detection sensitivity required, thus providing insight
for further detector development.