Biomedical subjects

Stephen M Hahn

Publications and source records attributed to Stephen M Hahn.

39 records · Page 3Linked to original sources

PubMedDate not supplied

Optical properties of human prostate at 732 nm measured in mediated photodynamic therapy.

Characterization of the tissue light penetration in prostate photodynamic therapy (PDT) is important to plan the arrangement and weighting of light sources so that sufficient light fluence is delivered to the treatment volume. The optical properties (absorption [mu(a)], transport scattering [mu(s)'] and effective attenuation [mu(eff)] coefficients) of 13 patients with locally recurrent prostate cancer were measured in situ using interstitial isotropic detectors. Measurements were made at 732 nm before and after motexafin lutetium (MLu)-mediated PDT in four quadrants. Optical properties were derived by applying the diffusion theory to the fluence rates measured at several distances (0.5-5 cm) from a point source. mu(a) and mu(s)' varied between 0.07 and 1.62 cm(-1) (mean 0.37 +/- 0.24 cm(-1)) and 1.1 and 44 cm(-1) (mean 14 +/- 11 cm(-1)), respectively. mu(a) was proportional to the concentration of MLu measured by an ex vivo fluorescence assay. We have observed, on average, a reduction of the MLu concentration after PDT, presumably due to the PDT consumption of MLu. mu(eff) varied between 0.91 and 6.7 cm(-1) (mean 2.9 +/- 0.7 cm(-1)), corresponding to an optical penetration depth (delta = 1/micro(eff)) of 0.1-1.1 cm (mean 0.4 +/- 0.1 cm). The mean penetration depth at 732 nm in human prostate is at least two times smaller than that found in normal canine prostates, which can be explained by a four times increase of the mean value of mu(s)' in human prostates. The mean light fluence rate per unit source strength at 0.5 cm from a point source was 1.5 +/- 1.1 cm(-2), excluding situations when bleeding occurs. The total number of measurements was N = 121 for all mean quantities listed above. This study showed significant inter- and intraprostatic differences in the optical properties, suggesting that a real-time dosimetry measurement and feedback system for monitoring light fluences during treatment should be considered for future PDT studies.

Humans↗

PubMedDate not supplied

Interstitial fluorescence spectroscopy in the human prostate during motexafin lutetium-mediated photodynamic therapy.

The in vivo fluorescence emission from human prostates was measured before and after motexafin lutetium (MLu)-mediated photodynamic therapy (PDT). A single side-firing optical fiber was used for both the delivery of 465 nm light-emitting diode excitation light and the collection of emitted fluorescence. It was placed interstitially within the prostate via a closed transparent plastic catheter. Fitting of the collected fluorescence emission spectra using the known fluorescence spectrum of 1 mg/kg MLu in an intralipid phantom yields a quantitative measure of the local MLu concentration. We found that an additional correction factor is needed to account for the reduction of the MLu fluorescence intensity measured in vivo due to strong optical absorption in the prostate. We have adopted an empirical correction formula given by C = (3.1 cm(-1)/micro's) exp (microeff x 0.97 cm), which ranges from approximately 3 to 16, with a mean of 9.3 +/-4.8. Using a computer-controlled step motor to move the probe incrementally along parallel tracks within the prostate we can determine one-dimensional profiles of the MLu concentration. The absolute MLu concentration and the shape of its distribution are confirmed by ex vivo assay and by diffuse absorption measurements, respectively. We find significant heterogeneity in photosensitizer concentration within and among five patients. These variations occur over large enough spatial scales compared with the sampling volume of the fluorescence emission that mapping the distribution in three dimensions is possible.

Humans↗

PubMedDate not supplied

Real-time in situ monitoring of human prostate photodynamic therapy with diffuse light.

Photodynamic therapy (PDT) requires oxygen to cause cellular and vascular tumor damage. Tissue oxygen concentration, in turn, is influenced by blood flow and blood oxygenation. Real-time clinical measurement of these hemodynamic quantities, however, is rare. This paper reports the development and application of a probe, combining diffuse reflectance spectroscopy (DRS) for measurement of tumor blood oxygenation and diffuse correlation spectroscopy (DCS) for measurement of tumor blood flow. The instrument was adapted for clinical use during interstitial prostate PDT. Three patients with locally recurrent prostate cancer received 2 mg/ kg motexafin lutetium (MLu) 3 h before illumination and a total light dose of 100 J/cm(2) at 150 mW/cm. Prostrate blood oxygen saturation (StO2) decreased only slightly (approximately 3%) after treatment. On the other hand, prostate blood flow and total hemoglobin concentration over the course of PDT decreased by 50% and 15%, respectively, suggesting MLu-mediated PDT has an anti-vascular effect. While it is certainly impossible to draw definite conclusions from measurements of only three patients, the observed differences in tumor blood flow and blood oxygenation responses during PDT can, in principle, be used to choose among tissue oxygen consumption models and therefore emphasize the potential clinical value for simultaneous monitoring of both parameters.

Dose-Response Relationship, Radiation↗