Online light dosimetry with real-time feedback was applied for temoporfin-mediated interstitial photodynamic therapy (PDT) of dog prostate. The aim was to investigate the performance of online dosimetry by studying the correlation between light dose plans and the tissue response, i.e., extent of induced tissue necrosis and damage to surrounding organs at risk. Light-dose planning software provided dose plans, including light source positions and light doses, based on ultrasound images. A laser instrument provided therapeutic light and dosimetric measurements. The procedure was designed to closely emulate the procedure for whole-prostate PDT in humans with prostate cancer. Nine healthy dogs were subjected to the procedure according to a light-dose escalation plan. About 0.15 mg/kg temoporfin was administered 72 h before the procedure. The results of the procedure were assessed by magnetic resonance imaging, and gross pathology and histopathology of excised tissue. Light dose planning and online dosimetry clearly resulted in more focused effect and less damage to surrounding tissue than interstitial PDT without dosimetry. A light energy dose–response relationship was established where the threshold dose to induce prostate gland necrosis was estimated from 20 to 30 J/cm2.
Optical techniques for tissue diagnostics currently are experiencing tremendous growth in biomedical applications, mainly due to their noninvasive, inexpensive, and real-time functionality. Here, we demonstrate a hand-held fiber optic probe instrument based on fluorescence/reflectance spectroscopy for precise tumor delineation. It is mainly aimed for brain tumor resection guidance with clinical adaptation to minimize the disruption of the standard surgical workflow and is meant as a complement to the state-of-the-art fluorescence surgical microscopy technique. Multiple light sources with fast pulse modulation and detection enable precise quantification of protoporphyrin IX (PpIX), tissue optical properties, and ambient light suppression. Laboratory measurements show the system is insensitive to strong ambient light. Validation measurements of tissue phantoms using nonlinear least squares support vector machines (LS-SVM) regression analysis demonstrate an error of <5% for PpIX concentration ranging from 400 to 1000 nM, even in the presence of large variations in phantom optical properties. The mean error is 3% for reduced scattering coefficient and 5% for blood concentration. Diagnostic precision of 100% was obtained by LS-SVM classification for in vivo skin tumors with topically applied 5-aminolevulinic acid during photodynamic therapy. The probe could easily be generalized to other tissue types and fluorophores for therapy guidance and monitoring.
Total resection of glioblastoma multiform (GBM), the most common and aggressive malignant brain tumor, is challenging among other things due to difficulty in intraoperative discrimination between normal and residual tumor cells. This project demonstrates the potential of a system based on a combination of autofluorescence and diffuse reflectance spectroscopy to be useful as an intraoperative guiding tool. In this context, a system based on 5 LEDs coupled to optical fibers was employed to deliver UV/visible light to the sample sequentially. Remitted light from the tissue; including diffuse reflected and fluorescence of endogenous and exogenous fluorophores, as well as its photobleaching product, is transmitted to one photodiode and four avalanche photodiodes. This instrument has been evaluated with very promising results by performing various tissue-equivalent phantom laboratory and clinical studies on skin lesions.
Glioblastoma multiforme (GBM) has long been known as the most common and aggressive form of brain malignancy. The morphological similarities of the malignant and surrounding tissue cause difficulties to distinct the tumors during surgery. In order to achieve better results in resecting malignant brain tumors, a fiber based optical system which can be used intraoperative is developed in this project. In this context, the system hardware details, system controlling interfaces and laboratory testing results are presented. Based on the results obtained from various tests with tissue-equivalent phantoms, the system is proved to have stable performance, robust structure, and have good linearity as well as high sensitivity to low PpIX concentration under strong ambient light conditions.
An ultrasound coupled handheld-probe-based optical fluorescence molecular tomography (FMT) system has been in
development for the purpose of quantifying the production of Protoporphyrin IX (PPIX) in aminolevulinic acid
treated (ALA), Basal Cell Carcinoma (BCC) in vivo. The design couples fiber-based spectral sampling of PPIX
fluorescence emission with a high frequency ultrasound imaging system, allowing regionally localized fluorescence
intensities to be quantified [1]. The optical data are obtained by sequential excitation of the tissue with a 633nm
laser, at four source locations and five parallel detections at each of the five interspersed detection locations. This
method of acquisition permits fluorescence detection for both superficial and deep locations in ultrasound field. The
optical boundary data, tissue layers segmented from ultrasound image and diffusion theory are used to estimate the
fluorescence in tissue layers. To improve the recovery of the fluorescence signal of PPIX, eliminating tissue autofluorescence
is of great importance. Here the approach was to utilize measurements which straddled the steep Qband
excitation peak of PPIX, via the integration of an additional laser source, exciting at 637 nm; a wavelength
with a 2 fold lower PPIX excitation value than 633nm.The auto-fluorescence spectrum acquired from the 637 nm
laser is then used to spectrally decouple the fluorescence data and produce an accurate fluorescence emission signal,
because the two wavelengths have very similar auto-fluorescence but substantially different PPIX excitation levels.
The accuracy of this method, using a single source detector pair setup, is verified through animal tumor model
experiments, and the result is compared to different methods of fluorescence signal recovery.
The in vivo performance of a Fluorescence Molecular Tomography system as a function of pathophysiological
parameters that determine the penetration of nonbinding fluorescent nanoparticle was examined through imaging of
a series of three tumor models. The pathophysiological parameters examined were, vessel density, interstitial fluid
pressure (IFP), and collagen content. Drug delivery and IFP were measured in vivo via fluorescence spectroscopy
and a fiber-optic coupled pressure probe. Vessel density and collagen content were determined ex vivo through
histochemical analysis. The kinetics of the 40 nm,10000 KDa, fluorescent particles, which were injected into the tail
vein of the mice, was monitored by sequential excitation of the tissue on and off the tumor site through employment
of sixteen source detector pairs interspersed linearly in reflectance geometry. Each optical fluorescence data set was
collected at discrete time intervals in order to monitor drug uptake for a period of 45 minutes. The kinetics of the
drug delivery and the average nanoparticle uptake were correlated with the vessel density, interstitial pressure and
collagen content. The results of the correlations were verified to be consistent with the published relationship
between the three pathophysiological parameters and nanoparticle drug delivery.
Accurate quantification of photosensitizers is in many cases a critical issue in photodynamic therapy. As a noninvasive and sensitive tool, fluorescence imaging has attracted particular interest for quantification in pre-clinical research. However, due to the absorption of excitation and emission light by turbid media, such as biological tissue, the detected fluorescence signal does not have a simple and unique dependence on the fluorophore concentration for different tissues, but depends in a complex way on other parameters as well. For this reason, little has been done on drug quantification in vivo by the fluorescence imaging technique. In this paper we present a novel approach to compensate for the light absorption in homogeneous turbid media both for the excitation and emission light, utilizing time-resolved fluorescence white Monte Carlo simulations combined with the Beer-Lambert law. This method shows that the corrected fluorescence intensity is almost proportional to the absolute fluorophore concentration. The results on controllable tissue phantoms and murine tissues are presented and show good correlations between the evaluated fluorescence intensities after the light-absorption correction and absolute fluorophore concentrations. These results suggest that the technique potentially provides the means to quantify the fluorophore concentration from fluorescence images.
The first results from a clinical study for Temoporfin-mediated photodynamic therapy (PDT) of low-grade (T1c) primary prostate cancer using online dosimetry are presented. Dosimetric feedback in real time was applied, for the first time to our knowledge, in interstitial photodynamic therapy. The dosimetry software IDOSE provided dose plans, including optical fiber positions and light doses based on 3-D tissue models generated from ultrasound images. Tissue optical property measurements were obtained using the same fibers used for light delivery. Measurements were taken before, during, and after the treatment session. On the basis of these real-time measured optical properties, the light-dose plan was recalculated. The aim of the treatment was to ablate the entire prostate while minimizing exposure to surrounding organs. The results indicate that online dosimetry based on real-time tissue optical property measurements enabled the light dose to be adapted and optimized. However, histopathological analysis of tissue biopsies taken six months post-PDT treatment showed there were still residual viable cancer cells present in the prostate tissue sections. The authors propose that the incomplete treatment of the prostate tissue could be due to a too low light threshold dose, which was set to 5 J/cm2.
Photodynamic therapy (PDT) is reviewed using the treatment of skin tumors as an example of superficial lesions and prostate cancer as an example of deep-lying lesions requiring interstitial intervention. These two applications are among the most commonly studied in oncological PDT, and illustrate well the different challenges facing the two modalities of PDT-superficial and interstitial. They thus serve as good examples to illustrate the entire field of PDT in oncology. PDT is discussed based on the Lund University group's over 20 yr of experience in the field. In particular, the interplay between optical diagnostics and dosimetry and the delivery of the therapeutic light dose are highlighted. An interactive multiple-fiber interstitial procedure to deliver the required therapeutic dose based on the assessment of light fluence rate and sensitizer concentration and oxygen level throughout the tumor is presented.
Photodynamic therapy (PDT) for the treatment of prostate cancer has been demonstrated to be a safe treatment
option capable of inducing tissue necrosis and decrease in prostate specific antigen (PSA). Research groups report
on large variations in treatment response, possibly due to biological variations in tissue composition and short-term
response to the therapeutic irradiation. Within our group, an instrument for interstitial PDT on prostate
tissue that incorporates realtime treatment feedback is being developed. The treatment protocol consists of
two parts. The first part incorporates the pre-treatment plan with ultrasound investigations, providing the
geometry for the prostate gland and surrounding risk organs, an iterative random-search algorithm to determine
near-optimal fiber positions within the reconstructed geometry and a Block-Cimmino optimization algorithm for
predicting individual fiber irradiation times. During the second part, the therapeutic light delivery is combined
with measurements of the light transmission signals between the optical fibers, thus monitoring the tissue effective
attenuation coefficient by means of spatially resolved spectroscopy. These data are then used as input for repeated
runs of the Block-Cimmino optimization algorithm. Thus, the irradiation times for individual fibers are updated
throughout the treatment in order to compensate for the influence of changes in tissue composition on the light
distribution at the therapeutic wavelength.
Fluorescence molecular tomography (FMT) suffers from inherent ill-posedness due to the vast number of
possible solutions to the reconstruction problem. To increase the robustness of such a problem one need
prior information. We present here a method for rendering a priori information of the position of a
fluorescent inclusion inside turbid media. The method utilizes solely two spectral bands within the
fluorescence spectrum emitted from the fluorophore. The method is presented and verified using
experimental data from a tissue phantom. The confinement is also used to impose weights onto the voxels
before the inversion of the linear set of equations describing the FMT problem.
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