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| Tim Baran |
A number of research groups, including Thomas Foster’s lab at the
PDT is an emerging cancer therapy that uses a combination of
light-sensitive drugs, known as photosensitizers, and targeted illumination to
create photochemical reactions that result in the destruction of cancer cells. Since
the treated area is limited by the penetration depth of the treatment light,
PDT has typically been used to treat superficial malignancies of the skin and
other easily accessible regions.
To make it work within the body, the photosensitizer is delivered systemically or locally, and allowed to accumulate in the tumor. Under image guidance, cylindrical diffusing fibers are then inserted into the tumor to deliver the treatment light. This treatment light is usually delivered by a laser with wavelengths varying from 630-700 nm (and beyond), depending on the photosensitizer used. As the diffusers used can be as long as 5 cm for large tumors, the required laser power at the source can approach or exceed 1 W.
As interstitial PDT is often performed in regions where
there is sensitive healthy tissue nearby, there is a need for careful treatment
planning. Towards that end, we have
developed a Monte Carlo simulation space that
allows for patient optical properties and anatomy to be incorporated into a
rigorous treatment plan.
Unlike radiation therapy, in which radiation doses can be
directly computed from CT scan data, calculations of optical dose require
knowledge of the patient’s optical properties, which can vary among patients
and even within a single patient. Therefore, spectroscopic determination of optical properties is required
before a treatment plan can be formulated.
A number of techniques exist to do this. In our case, we use a custom optical probe
that is inserted into the treatment region and a Monte Carlo based fitting algorithm in order
to extract optical properties. These
extracted optical properties are then combined with CT image data from the
patient in order to build an optical and anatomical map of the patient in our
simulation space. The number of
diffusers, and the amount of light delivered by them, can then be optimized
using a constrained nonlinear optimization algorithm. This ensures that tumor tissues receive a physician-prescribed
light dose, while damage to healthy tissue is minimized.
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| Simulated patient data showing the insertion of four cylindrical diffusing fibers for photodynamic therapy of head and neck cancers |
My work thus far has been preclinical, using simulated data
sets and animal models. We are actively
seeking to translate interstitial PDT into the clinic at the University of Rochester
Medical Center for treatment of cholangiocarcinoma, cancers of the head and
neck, and deep-tissue microbial infections.
TIM BARAN is a PhD candidate in the Institute
of Optics at the University
of Rochester (Rochester , NY
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