Lasers in medicine: therapeutic and monitoring applications

Our laboratory is currently investigating the potential of interstitial laser therapy as an effective modality for the treatment of disease, including the thermal destruction of small solid tumors. The research is currently focused on the treatment of prostate cancer. However, the general goal of this work is to optimize and control interstitial thermal therapy for a variety of applications. To this end, two related investigations are being undertaken.

1) Knowledge of tissue optical properties is essential in order to plan and control Interstitial Laser Photocoagulation (ILP). The penetration of optical energy in tissue is governed by the optical absorption and optical scattering properties. Once absorbed the optical energy is converted to thermal energy. Generally, tissue optical properties are determined, based on measurements of transmission and reflection of light through excised (ex vivo) tissue samples. Compilations of ex vivo tissue optical properties can be found in the literature. However, the influence of perfused blood (in vivo tissues) on optical properties is not well known. The validity of using ex vivo optical properties to plan laser therapy is therefore questioned. A novel technique is being developed to determine tissue optical properties, source/sensor location, and source power from multipoint measurements of optical fluence and temperature, data routinely available during laser irradiation.

2) Confining the lethal thermal effects to a target volume requires control over the spatial and temporal temperature elevation. In order to control treatments, an on-line multipoint temperature and thermal damage control algorithm is being developed to provide for on-line adjustment of the heating protocol (laser power, exposure duration and source locations). The required input to the algorithm will be 3D temperature maps reconstructed from sparse measured data sets and/or complete 3D temperaure data obtained from MRI thermometry. One challenge of this work will be to include the effects of changing tissue optical properties.

These techniques will be developed using fluoroptic thermometry and medical diode laser systems in our laboratory. Projects can involve both computation and experimentation, including thermal and optical modeling, visualization techniques and hardware development.

Graduate Students:

Selected References:

• Ying Fan, Andreas Mandelis, Gloria Spirou, I. Alex Vitkin and William M. Whelan, “Laser photothermoacoustic frequency swept heterodyned lock-in depth profilometry in turbid tissue phantoms”, Physical Review E, 72, 051908, 2005.

• LCL Chin, WM Whelan and IA Vitkin, “Information content of point radiance measurements in turbid media: implications for interstitial optical property quantification”, Journal of the Optical Society of  America, (in press), 2005.

• G. Spirou, A. Oraevsky, IA Vitkin and WM Whelan, “Optical and acoustic properties at 1064nm of polyvinyl chloride-plastisol (PCP) for use as  a tissue phantom in biomedical photoacoustics”, Physics in Medicine and Biology, 50, N141-N153, 2005.

• Sean R H Davidson, I. Alex Vitkin, Michael D. Sherar and William M. Whelan, "Characterization of measurement artefacts in fluoroptic temperature sensors: Implications for laser thermal therapy at 810 nm" Lasers in Surgery and Medicine, 36, 297-306 2005.

• William M. Whelan, Lee C.L. Chin, Sean R. Davidson and I. Alex Vitkin, “A novel strategy for monitoring laser thermal therapy based on changes in optothermal properties of heated tissues”, International Journal of Thermophysics , 26, 233-241, 2005.

• Lee CL Chin, Brian C Wilson, William M Whelan and I Alex Vitkin “Radiance-based method for on-line determination of thermal coagulation extent during laser interstitial thermal therapy” Optics Letters, 29, 959-961, 2004