THIS IS FOR THE SESSION "CAPABILITIES OF 5-ALA"
The accumulation of the fluorescent photosensitizer protoporphyrin IX (PpIX) after systemic administration of 5-ALA proved high tumor selectivity and led to intra-operative fluorescence guidance during resection of malignant glioma. 5-ALA therefore also promises to be useful for PDT of malignant glioma. Preclinical investigations resulted in the establishment of an appropriate treatment planning strategy and treatment parameters. This can be outlined as follows: interstitial placement of cylindrical diffuser fibers (1 to 4 cm diffuser length) by stereotaxy after careful planning on CT/MRI scans, such that fibers are approximately 1 cm apart and as close as 3-4 mm from the contrast uptaking tumor border. Aim of the irradiation parameters (200 mW/cm diffuser length for 1 hour) is to reach >95% photobleaching of PpIX in at least one optical penetration depth (approx. 3 mm) from the fibers. The therapeutic penetration depth can be expected to reach significantly deeper and kill glioma cells within parts of the infiltration zone, which are no more highlighted by Gd-contrast uptake. So far, inoperable de novo and recurrent malignant glioma with sizes up to 3 cm in diameter proved amenable in clinical investigations. Intriguing longterm progression free and overall survivals led to the design of prospective clinical trials, which are expected to start recruitment in 2019.
Further research should focus on individualizing treatment parameters, further improve PpIX accumulation, including the sensitization of cancer stem cells and explore the role of immune stimulation by PDT, including the possible synergistic effect of immune checkpoint inhibitors.
Interstitial photodynamic therapy (iPDT) is currently being investigated as a light-based treatment option for highly malignant brain tumours (glioblastomas/GBM). To obtain a sufficient irradiation of the tumour, quantitative knowledge about the light propagation in the tissue is required for the light dosimetry calculations underlying the clinical treatment planning. To individualize the light dosimetry calculations, the optical properties of the irradiated tissue need to be determined in-vivo. A novel approach for this purpose is based on the direction-resolved light detection within the tissue, using a rotating optical side-view probe. During measurement, the tissue is irradiated via a separate interstitially placed light applicator, and from the angular dependence of the recorded signal the optical tissue properties are calculated, based on a solution of the radiative transfer equation (RTE). Measurements were performed on liquid tissue phantoms and biological tissue samples. As a result, an over- and underestimation of the calculated optical absorption and scattering coefficients may arise in some situations, but the effective attenuation coefficient remains largely unaffected and corresponds well with literature values.
Thermography is used in many application areas like non-destructive testing, architecture or zoology. Approaches to use thermography for medical diagnostics are usually focused on the detection of tumors. The usefulness and specificity for this purpose has been debated. Nevertheless it seems reasonable to evaluate the applicability of thermography as a tool for determining temperature distributions on the surface of, e.g., light diffusers or biological tissue in the field of laser medicine. The assessment of tissue-heating in treatments like interstitial photodynamic therapy (iPDT) is of particular interest since additional tissue damage due to tissue heating is usually undesired and has thus to be avoided. Monte Carlo based simulations of the expected heat distribution in tissue are based on idealized setups. They usually omit certain characteristics of fibers, like inhomogeneities in a light diffuser or losses at components such as internal mirrors, that might potentially result in local hot spots and therefore in heating beyond an acceptable temperature. Experimental techniques based on thermocouples, or similar point-based temperature measurement devices, provide only a limited view of the temperature distribution inside or at the surface of the treated tissue. As a high resolution non-contact wide-field technique thermography although has some limitations. We present an evaluation of the usefulness of thermographic methods for recording the heat distribution on tissue and tissue phantom surfaces during laser treatment in an iPDT-like setup and compare the results with Monte Carlo based simulations.
Knowledge of tissue optical properties, in particular the absorption μa and the reduced scattering coefficient μs′, is required for diagnostic and therapeutic applications in which the light distribution during treatment has to be known. As it is generally very difficult to obtain this information with sufficient accuracy in vivo, optical properties are often approximately determined on ex vivo tissue samples. In this case, the obtained optical properties may strongly depend on the sample preparation. The extent of the expectable preparation-dependent differences was systematically investigated in comparative measurements on dissected and homogenized porcine tissue samples (liver, lung, brain, and muscle). These measurements were performed at wavelengths 520, 635, 660, and 785 nm, using a dual-step reflectance device and at a spectral range of 515 to 800 nm with an integrating sphere setup. In a third experiment, the density of tissue samples (dissected and homogenized) was investigated, as the characteristic of the packaging of internal tissue structures strongly influences the absorption and scattering. The standard errors of the obtained absorption and reduced scattering coefficients were found to be reduced in case of homogenized tissue. Homogenizing the tissues also allows a much easier and faster sample preparation, as macroscopic internal tissue structures are destroyed in the homogenized tissue so that a planar tissue sample with well-defined thickness can easily and accurately be prepared by filling the tissue paste into a cuvette. Consequently, a better reproducibility result was obtained when using homogenized samples. According to the density measurements accomplished for dissected and homogenized tissue samples, all types of tissues, except lung, showed a decrease in the density due to the homogenization process. The presented results are in good agreement for μs′ regardless of the preparation procedure, whereas μa differs, probably influenced by blood content and dehydration. Because of faster and easier preparation and easier sample positioning, homogenization prior to measurement seems to be suitable for investigating the optical properties ex vivo. Additionally, by means of using the homogenization process, the sample size and thickness do not need to be particularly large, as is the case for most biopsies from the OR.
Malignant gliomas are a devastating brain tumor disease with very poor prognosis. Stereotactic biopsy sampling is routinely used in larger neurosurgical centers to confirm the diagnosis of a suspected brain tumor. This procedure is associated with risk of blood vessel rupture as well as false-negative results. Recent investigations suggest a potential of light-based techniques to improve both therapy and diagnosis of GBM.
Optical guidance can be utilized to improve the biopsy sampling procedure in terms of safety, reliability, and efficacy. Recording of optical signals (transmission, remission, fluorescence) can be potentially integrated into a biopsy needle for providing optical detection of tumor tissue and blood vessel recognition during the biopsy sampling.
Optical signals can also be used for monitoring purposes during photodynamic therapy. Here, fluorescence signals recorded before the treatment indicate the presence and accumulation level of photosensitizer, while photobleaching of the photosensitizer fluorescence during the treatment can be used as a measure of the effectiveness of the therapy. Finally, transmitted light can reveal problematic tissue-optical conditions as well as changes of the optical properties of the treated tissue, which may be relevant with regard to treatment prognosis and strategy. Different optical concepts for interstitial PDT monitoring and optical tissue property assessment are presented.
Malignant gliomas are a devastating brain tumor disease with very poor prognosis. Stereotactic biopsy sampling is routinely used in larger neurosurgical centers to confirm the diagnosis of a suspected brain tumor. This procedure is associated with risk of blood vessel rupture as well as false-negative results. Recent investigations suggest a potential of light-based techniques to improve both therapy and diagnosis of GBM. Optical guidance can be utilized to improve the biopsy sampling procedure in terms of safety, reliability, and efficacy. Recording of optical signals (transmission, remission, fluorescence) can be potentially integrated into a biopsy needle for providing optical detection of tumor tissue and blood vessel recognition during the biopsy sampling. Optical signals can also be used for monitoring purposes during photodynamic therapy. Here, fluorescence signals recorded before the treatment indicate the presence and accumulation level of photosensitizer, while photobleaching of the photosensitizer fluorescence during the treatment can be used as a measure of the effectiveness of the therapy. Finally, transmitted light can reveal problematic tissue-optical conditions as well as changes of the optical properties of the treated tissue, which may be relevant with regard to treatment prognosis and strategy. Different optical concepts for interstitial PDT monitoring and optical tissue property assessment are presented.
5-aminolevulinic-acid-(5-ALA)-induced protoporphyrin IX (PpIX) fluorescence may be used to improve stereotactic brain tumor biopsies. In this study, the sensitivity of PpIX-based tumor detection has been investigated for two potential excitation wavelengths (405 nm, 633 nm). Using a 200 μm fiber in contact with semi-infinite optical phantoms containing ink and Lipovenös, PpIX detection limits of 4.0 nM and 200 nM (relating to 1 mW excitation power) were determined for 405 nm and 633 nm excitation, respectively. Hence, typical PpIX concentrations in glioblastomas of a few μM should be well detectable with both wavelengths. Additionally, blood layers of selected thicknesses were placed between fiber and phantom. Red excitation was shown to be considerably less affected by blood interference: A 50 μm blood layer, for instance, blocked the 405- nm-excited fluorescence completely, but reduced the 633-nm-excited signal by less than 50%. Ray tracing simulations demonstrated that – without blood layer – the sensitivity advantage of 405 nm rises for decreasing fluorescent volume from 50-fold to a maximum of 100-fold. However, at a tumor volume of 1 mm3, which is a typical biopsy sample size, the 633-nm-excited fluorescence signal is only reduced by about 10%. Further simulations revealed that with increasing fiber-tumor distance, the signal drops faster for 405 nm. This reduces the risk of detecting tumor tissue outside the needle’s coverage, but diminishes the overlap between optically and mechanically sampled volumes. While 405 nm generally offers a higher sensitivity, 633 nm is more sensitive to distant tumors and considerably superior in case of blood-covered tumor tissue.
Stereotactic biopsy procedure is performed to obtain a tissue sample for diagnosis purposes. Currently, a fiber-based mechano-optical device for stereotactic biopsies of brain tumors is developed. Two different fluorophores are employed to improve the safety and reliability of this procedure: The fluorescence of intravenously applied indocyanine green (ICG) facilitates the recognition of blood vessels and thus helps minimize the risk of cerebral hemorrhages. 5- aminolevulinic-acid-induced protoporphyrin IX (PpIX) fluorescence is used to localize vital tumor tissue. ICG fluorescence detection using a 2-fiber probe turned out to be an applicable method to recognize blood vessels about 1.5 mm ahead of the fiber tip during a brain tumor biopsy. Moreover, the suitability of two different PpIX excitation wavelengths regarding practical aspects was investigated: While PpIX excitation in the violet region (at 405 nm) allows for higher sensitivity, red excitation (at 633 nm) is noticeably superior with regard to blood layers obscuring the fluorescence signal. Contact measurements on brain simulating agar phantoms demonstrated that a typical blood coverage of the tumor reduces the PpIX signal to about 75% and nearly 0% for 633 nm and 405 nm excitation, respectively. As a result, 633 nm seems to be the wavelength of choice for PpIX-assisted detection of high-grade gliomas in stereotactic biopsy.
Medical laser applications based on widespread research and development is a very dynamic and increasingly popular field from an ecological as well as an economic point of view. Conferences and personal communication are necessary to identify specific requests and potential unmet needs in this multi- and interdisciplinary discipline. Precise gathering of all information on innovative, new, or renewed techniques is necessary to design medical devices for introduction into clinical applications and finally to become established for routine treatment or diagnosis. Five examples of successfully addressed clinical requests are described to show the long-term endurance in developing light-based innovative clinical concepts and devices. Starting from laboratory medicine, a noninvasive approach to detect signals related to iron deficiency is shown. Based upon photosensitization, fluorescence-guided resection had been discovered, opening the door for photodynamic approaches for the treatment of brain cancer. Thermal laser application in the nasal cavity obtained clinical acceptance by the introduction of new laser wavelengths in clinical consciousness. Varicose veins can be treated by innovative endoluminal treatment methods, thus reducing side effects and saving time. Techniques and developments are presented with potential for diagnosis and treatment to improve the clinical situation for the benefit of the patient.
Objective: Improvement of the clinical outcome of glioblastoma (GBM) patients by employment of fluorescence and
photosensitization on the basis of 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (PpIX).
Methods: In this report the focus is laid on the use of tumor selective PpIX fluorescence for stereotactic biopsy
sampling and intra-operative treatment monitoring. In addition, our current concept for treatment planning is presented.
For stereotactic interstitial photodynamic therapy (iPDT), radial diffusers were implanted into the contrast enhancing
tumor volume. Spectroscopic measurements of laser light transmission and fluorescence between adjacent fibers were
performed prior, during and post PDT.
Results: PpIX concentrations in primary glioblastoma tissue show high intra- and inter-patient variability, but are
usually sufficient for an effective PDT. During individual treatment attempts with 5-ALA based GBM-iPDT,
transmission and fluorescence measurements between radial diffusers gave the following results: 1. In some cases,
transmission after PDT is considerably reduced compared to the value before PDT, which may be attributable to a
depletion of oxygenated hemoglobin and/or diffuse bleeding. 2. PpIX fluorescence is efficiently photobleached during
PDT in all cases.
Conclusion: iPDT with assessment of PpIX fluorescence and photobleaching is a promising treatment option.
Individualization of treatment parameters appears to bear a potential to further improve clinical outcomes.
Objective: During laser assisted laparoscopic intervention smoke occurs reducing the clear vision to the target. Simply
smoke suction is not possible with respect to deflating / enflating capabilities of the belly. Thus the clinical question arise
if the use of different wavelength may show similar smoke development or whether is it possible to reduce the smoke
development by wavelength selection.
Materials and Methods: Tissue test model was “Bavarian Leberkäse”. A special container set-up was created to collect
the laser induced smoke. Smoke was suctioned through a capillary. The amount of light scattered by the smoke particles
when flowing through this capillary was measured. Ablation parameter was continuous mode and10W at the end of a
400μm bare fibre for the wavelengths 980nm, 1350nm and 1470nm. Additional the optical transmission was measured.
The vaporized tissue volume was measured.
Results: Light scattering, optical parameters and vaporized tissue volume were correlated. Measurement showed
reproducible results. While the time to get first signal of scattered light in case of 1470nm is shorter compared the other
wavelength, the ratio of scatter-signal to ablation rate showed only a trend increase when longer wavelength were used.
Conclusion: Tissue absorbers and carbonized tissue properties are relevant for smoke development resulting in an
increased SI / AR ratio trend. Thus the expert physician in laparoscopic intervention should also be an expert in lasertissue
interaction. Cutting without carbonization gained advantages.
Objective: When a stereotactic biopsy is taken to enable histopathological diagnosis of a suspected brain tumor, it is
essential to i) do this safely, that is not injure a major blood vessel and ii) to obtain relevant vital material from the
tumor. We are investigating the suitability of Indocyanine Green (ICG) fluorescence for blood vessel recognition and 5-
Aminolevulinic acid (5-ALA) induced Protoporphyrin IX (PpIX) fluorescence for identification of proliferative brain
Methods: A fiber-optic endoscopic approach was studied to generate and detect both fluorescence signals. PpIX
concentrations in brain tumors have been measured by chemical extraction. Preliminary equipment was studied in a
Results: PpIX-concentrations in glioblastoma tissue showed high inner- and inter-patient variability, but each patient
out of 15 with interpretable data showed at least one sample with a PpIX-concentration exceeding 2.4 μmol/l, which is
easily detectable by state-of-the-art fiberoptic fluorescence spectroscopy and imaging. The imaging fluoroscope with
30,000 pixels resolution could be introduced through a position controlled stereotactic needle. ICG-fluorescence from
vessels with diameters ≥ 0.1 mm can be detected with a contrast of 2-2.5 against surrounding tissue.
Conclusion: Fluorescence detection during stereotactic biopsy might increase safety and precision of the procedure