News & Events

Gal Shafirstein, Ph.D.

Posted on October 26, 2018


Date - October 26, 2018
1:00 pm - 2:00 pm


Dr. Gal Shafirstein, D.Sc.
Professor of Oncology and Full Member
Director of Photodynamic Therapy (PDT) Clinical Research
PDT Center at the Department of Cell Stress Biology
Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA
Talk Title: Photodynamic Therapy Dosimetry – From the Clinic to the Bench and Back


Photodynamic therapy (PDT) dosimetry has been traditionally defined as the product of the local
concentration of the photosensitizer multiplied by the applied light dose (J/cm 2 ). This concept holds true
if the light dose rate (i.e. irradiance, mW/cm 2 ) is low enough so that there is efficient oxygen
consumption during PDT. The irradiance within the target tumor, and thus dosimetry, depends on the
method of illumination: external beam PDT (EB-PDT) or interstitial PDT (I-PDT). While EB-PDT is used to
treat superficial and thin tumors, I-PDT is used to treat deeply seated and large tumors. To date, the
reported tumor response to EB-PDT has been better in comparison to I-PDT. Using computer modeling,
we investigated the differences in irradiance between EB-PDT and I-PDT, and formulated a hypothesis:
that using our computer model we can define light irradiance that will improve the response and cure
rate in I-PDT. This hypothesis was tested in preclinical studies (on the bench), and found to be true in
rigor studies using two animal models. The results of these studies were used to develop a clinical study
(back to clinic) to administer I-PDT in patients with locally advanced head and neck cancer who failed to
respond to standard therapies.

In this talk, a brief overview of EB-PDT and I-PDT will be presented. We will review the principles of light
dosimetry, and present the study design and results that led to the development of a modified light
dosimetry for I-PDT. We will discuss how a clinical observation and research led to a preclinical study
that is used to guide a clinical study in I-PDT.