研究不同光敏剂诱导的光动力疗法对人白血病细胞的杀伤作用

目的 研究并比较3种卟啉类光敏剂——血卟啉衍生物(HpD)、癌光啉(PsD007)和血卟啉 单甲醚(HMME)诱导的光动力疗法(PDT)对白血病细胞K562的杀伤效应.方法 以人白血病细胞K562为研究对象,分为对照组和PDT组,以梯度浓度的光敏剂与K562细胞共同孵育,经不同能量光照后,用噻唑蓝(MTT)法测定PDT对K562细胞的杀伤作用.结果 与对照组相比,PDT对K562细胞有明显杀伤作用,并随着光敏剂浓度的增加和光照能量的增大,效果增强.PsD007-PDT和HMME-PDT的效果都明显优于HpD-PDT(P＜0.05);而当光敏剂质量浓度较大(25 μg/ml)或能量密度较大(7.2 J/cm2)时,PsD007-PDT的作用效果优于HMME-PDT.结论 PDT对人白血病细胞K562具有明显的杀伤作用,其对细胞的抑制率具有显著的剂量效应关系;PDT对K562的杀伤效应与光敏剂种类有关,HpD-PDT的杀伤效果不如PsD007和HMME;在较高能量密度和较大光敏剂浓度的条件下,PsD007-PDT的效果优于HMME-PDT.     

新型卟啉类光敏药物介导的PDT对两种胃癌细胞HGC27和MGC803的杀伤效应

目的 观察本实验室自行合成的新型卟啉类光敏药物对2种人胃癌细胞HGC27和MGC803的光动力学治疗(PDT)作用及作用机制.方法 以人胃癌细胞HGC27和MGC803为实验细胞株.实验分为4组:空白对照组(无药物孵育、无光照),单纯光敏药物组(药物孵育、无光照),单纯光照组(无药物孵育、有光照),光敏药物+光照组(药...     

光动力治疗中激光辐射有效吸收剂量

光动力治疗中激光辐射有效吸收剂量郑蔚谢树森（福建师范大学激光研究所，福州３５０００７）ＡｂｓｔｒａｃｔＲｅｓｅａｒｃｈｅｒｓｔｙｐｉｃａｌｙｕｓｅｒａｄｉａｎｔｅｘｐｏｓｕｒｅｏｎｔｈｅｓｕｒｆａｃｅｏｆｔｉｓｕｅｔｏｅｖａｌｕａｔｅｔｈｅｌｉｇｈｔ...     

Photodynamic therapy as an alternative antimicrobial modality for oral infections.

Infections of the mouth are mostly local in nature, but if left untreated, may lead to potentially life-threatening conditions. Mouth infections, such as caries, pulpitis, periodontal disease, and oral mucosal infections, such as mouth ulcers, are readily accessible and thus well suited to photodynamic therapy (PDT). Many organisms, which may cause infections in the oral cavity, have been found to be susceptible to PDT to varying degrees. Several photosensitizers have been shown to be effective against target organisms without inducing damage to the host tissues. The use of appropriate photosensitizers and light doses can eradicate virtually all organisms in the region, but in the oral cavity where there is a balance of native microflora, this would potentially be a problem leading to the overgrowth of opportunistic organisms. This may be overcome using a photosensitizer linked to an antibody recognizing the target organisms. At present, treatment of infections with PDT appears best for localized and superficial infections. Treatment of deeply seated infections, such as abscesses, may also be possible with improvements in the delivery of the sensitizer and light. PDT has the potential to become established as an alternative antimicrobial approach for oral infections and deserves further evaluation.     

Determination of the tumor tissue optical properties during and after photodynamic therapy using inverse Monte Carlo method and double integrating sphere between 350 and 1000 nm

Photodynamic therapy (PDT) efficacy depends on the amount of light distribution within the tissue. However, conventional PDT does not consider the laser irradiation dose during PDT. The optical properties of biological tissues (absorption coefficient μ(a), reduced scattering coefficient μ's), anisotropy factor g, refractive index, etc.) help us to recognize light propagation through the tissue. The goal of this paper is to acquire the knowledge of the light propagation within tissue during and after PDT with the optical property of PDT-performed mouse tumor tissue. The optical properties of mouse tumor tissues were evaluated using a double integrating sphere setup and the algorithm based on the inverse Monte Carlo method in the wavelength range from 350 to 1000 nm. During PDT, the μ(a) and μ's were not changed after 1 and 5 min of irradiation. After PDT, the μ's in the wavelength range from 600 to 1000 nm increased with the passage of time. For seven days after PDT, the μ's increased by 1.7 to 2.0 times, which results in the optical penetration depth decreased by 1.4 to 1.8 times. To ensure an effective procedure, the adjustment of laser parameters for the decreasing penetration depth is recommended for the re-irradiation of PDT.     

The role of photodynamic therapy (PDT) physics

Photodynamic therapy (PDT) is an emerging treatment modality that employs the photochemical interaction of three components: light, photosensitizer, and oxygen. Tremendous progress has been made in the last 2 decades in new technical development of all components as well as understanding of the biophysical mechanism of PDT. The authors will review the current state of art in PDT research, with an emphasis in PDT physics. They foresee a merge of current separate areas of research in light production and delivery, PDT dosimetry, multimodality imaging, new photosensitizer development, and PDT biology into interdisciplinary combination of two to three areas. Ultimately, they strongly believe that all these categories of research will be linked to develop an integrated model for real-time dosimetry and treatment planning based on biological response.     

Updated results of a phase I trial of motexafin lutetium-mediated interstitial photodynamic therapy in patients with locally recurrent prostate cancer.

Locally recurrent prostate cancer after treatment with radiation therapy is a clinical problem with few acceptable treatments. One potential treatment, photodynamic therapy (PDT), is a modality that uses laser light, drug photosensitizer, and oxygen to kill tumor cells through direct cellular cytotoxicity and/or through destruction of tumor vasculature. A Phase I trial of interstitial PDT with the photosensitizer Motexafin lutetium was initiated in men with locally recurrent prostate cancer. In this ongoing trial, the primary objective is to determine the maximally tolerated dose of Motexafin lutetium-mediated PDT. Other objectives include evaluation of Motexafin lutetium uptake from prostate tissue using a spectrofluorometric assay and evaluation of optical properties in the human prostate. Fifteen men with biopsy-proven locally recurrent prostate cancer and no evidence of distant metastatic disease have been enrolled and 14 have been treated. Treatment plans were developed using transrectal ultrasound images. The PDT dose was escalated by increasing the Motexafin lutetium dose, increasing the 732 ran light dose, and decreasing the drug-light interval. Motexafin lutetium doses ranged from 0.5 to 2 mg/kg administered IV 24, 6, or 3 hr prior to 732 ran light delivery. The light dose, measured in real time with in situ spherical detectors was 25-100 J/cm2. Light was delivered via optical fibers inserted through a transperineal brachytherapy template in the operating room. Optical property measurements were made before and after light therapy. Prostate biopsies were obtained before and after light delivery for spectrofluorometric measurements of photosensitizer uptake. Fourteen patients have completed protocol treatment on eight dose levels without dose-limiting toxicity. Grade I genitourinary symptoms that are PDT related have been observed. One patient had Grade II urinary urgency that was urinary catheter related. No rectal or other gastrointestinal PDT-related tox-icities have been observed to date. Measurements of Motexafin lutetium demonstrated the presence of photosensitizer in prostate tissue from all patients. Optical property measurements demonstrated substantial heterogeneity in the optical properties of the human prostate gland which supports the use of individualized treatment planning for prostate PDT.     

Protoporphyrin IX fluorescence photobleaching increases with the use of fractionated irradiation in the esophagus

Fluorescence measurements have been used to track the dosimetry of photodynamic therapy (PDT) for many years, and this approach can be especially important for treatments with aminolevulinic-acid-induced protoporphyrin IX (ALA-PpIX). PpIX photobleaches rapidly, and the bleaching is known to be oxygen dependent, and at the same time, fractionation or reduced irradiance treatments have been shown to significantly increase efficacy. Thus, in vivo measurement of either the bleaching rate and/or the total bleaching yield could be used to track the deposited dose in tissue and determine the optimal treatment plans. Fluorescence in rat esophagus and human Barrett's esophagus are measured during PDT in both continuous and fractionated light delivery treatment, and the bleaching is quantified. Reducing the optical irradiance from 50 to 25 mWcm did not significantly alter photobleaching in rat esophagus, but fractionation of the light at 1-min on and off intervals did increase photobleaching up to 10% more (p value=0.02) and up to 25% more in the human Barrett's tissue (p value<0.001). While two different tissues and two different dosimetry systems are used, the data support the overall hypothesis that light fractionation in ALA-PpIX PDT esophageal treatments should have a beneficial effect on the total treatment effect.     

Vascular and cellular targeting for photodynamic therapy

Photodynamic therapy (PDT) involves the combination of photosensitizers (PS) with light as a treatment, and has been an established medical practice for about 10 years. Current primary applications of PDT are age-related macular degeneration (AMD) and several types of cancer and precancer. Tumor vasculature and parenchyma cells are both potential targets of PDT damage. The preference of vascular versus cellular targeting is highly dependent upon the relative distribution of photosensitizers in each compartment, which is governed by the photosensitizer pharmacokinetic properties and can be effectively manipulated by the photosensitizer drug administration and light illumination interval (drug-light interval) during PDT treatment, or by the modification of photosensitizer molecular structure. PDT using shorter PS-light intervals mainly targets tumor vasculature by confining photosensitizer localization within blood vessels, whereas if the sensitizer has a reasonably long pharmacokinetic lifetime, then PDT at longer PS-light intervals can induce more tumor cellular damage, because the photosensitizer has then distributed into the tumor cellular compartment. This passive targeting mechanism is regulated by the innate photosensitizer physicochemical properties. In addition to the passive targeting approach, active targeting of various tumor endothelial and cellular markers has been studied extensively. The tumor cellular markers that have been explored for active photodynamic targeting are mainly tumor surface markers, including growth factor receptors, low-density lipoprotein (LDL) receptors, transferrin receptors, folic acid receptors, glucose transporters, integrin receptors, and insulin receptors. In addition to tumor surface proteins, nuclear receptors are targeted, as well. A limited number of studies have been performed to actively target tumor endothelial markers (ED-B domain of fibronectin, VEGF receptor-2, and neuropilin-1). Intracellular targeting is a challenge due to the difficulty in achieving sufficient penetration into the target cell, but significant progress has been made in this area. In this review, we summarize current studies of vascular and cellular targeting of PDT after more than 30 years of intensive efforts.     

Wedge-shaped applicator for additional light delivery and dosimetry in the diaphragmal sinus during photodynamic therapy for malignant pleural mesothelioma

In situ light dosimetry during photodynamic therapy (PDT) of malignant pleural mesothelioma (MPM) after tumour resection facilitates the delivery of a controlled light distribution to the inner thoracic surface. Illumination of the diaphragm-induced sinus, however, remains difficult. Our aim was to develop a wedge-shaped light applicator with incorporated light dosimetry to deliver an additional fluence limited to the sinus. The wedge-shaped applicator contains a cylindrical diffuser for light delivery and two isotropic detectors for simultaneous light dosimetry. These detectors were placed at strategic positions where the fluence rate is maximal or minimal (middle and edge). Prior to its clinical use, the performance of the sinus light applicator was tested in several optical tissue phantoms with different optical properties. The fluence rate distribution over the surface of the applicator showed little change when the wedge was submerged in four different optical phantoms. During clinical PDT of MPM the applicator had to be re-located manually four times in order to give an additional fluence of approximately 2 J cm(-2) to the entire sinus. The light applicator enables dosimetry-controlled light delivery for additional illumination of the sinus region that is often under-illuminated during thoracic integral illumination of MPM.     

A new method for photodynamic therapy of melanotic melanoma -- effects of depigmentation with violet light photodynamic therapy

Melanotic melanomas have a poor response to photodynamic therapy (PDT). The reason for this is that melanin absorbs light over the entire wavelength region used for PDT (400-750 nm). Photobleaching of melanin is an approach to overcome this obstacle. In the present work, reflectance spectroscopy was applied to study depigmentation of human and murine skin with different melanin contents, and effects induced by PDT with topical application of methyl 5-aminolevulinate (MAL) on B16F10 melanotic melanomas transplanted to nude mice. Depigmentation and inhibition of tumor growth after violet light (420 nm) exposure, red light (634 nm) exposure, and combinations of both were studied. Reflectance spectroscopy was suitable for evaluation of the pigmentation of both human and murine skin. Skin depigmentation leads to increase in reflectance. PDT with violet light bleached some of the melanin in the skin above the B16F10 melanomas, and possibly also in the upper part of the melanomas. This resulted in a larger growth inhibition of tumors first given PDT with violet light and then with red light compared to treatments using the reverse order of illumination, namely, red light before violet light. It is concluded that violet light PDT can bleach melanin in melanotic tumors and therefore increase their sensitivity to red light PDT. This finding indicates a new PDT modality that can be further developed for treatment of superficial melanotic melanomas and possibly other diseases where pigmentation is a problem.     

Influence of uterine cervix shape on photodynamic therapy efficiency

The goal of practical photodynamic therapy (PDT) dosimetry is to optimize the distribution of a light dose delivered to tissue by selecting the irradiation time and geometry to match the geometry and optical properties of the tumor and surrounding tissue. Homogeneous irradiation is among one of the sources of correct PDT dosimetry. The goal of this study is to model and predict the influence of the shape of a treated organ in need of light dose correction. Thus efficiency of light delivery to the tissue volume is defined and calculated with shape factors of the uterine cervix as parameters. Two cases (parallel and divergent beam) of enlightening configuration are investigated. The calculations presented extend PDT dosimetry with the influence of the shape of the uterine cervix on PDT necrosis depth. This allows for photodynamic excitation light dose correction for more reliable treatments.     

Light penetration in the human prostate: a whole prostate clinical study at 763 nm

Photodynamic therapy (PDT) is being investigated as a treatment for localized prostate cancer. Photodynamic therapy uses a photosensitizing drug which is activated by a specific wavelength of light, in the presence of oxygen. The activated drug reacts with tissue oxygen to produce reactive oxygen species which are responsible for localized tissue necrosis. One of the determinants of the PDT effect is the penetration of light in the prostate. This study assesses the penetration depth of 763 nm light throughout the prostate. Eight men undergoing multiple hollow needle insertion for high dose rate brachytherapy were recruited. 763 nm light, produced by a diode laser, was delivered to the prostate using cylindrically diffusing optical fibers within the plastic needles. Light was detected at different distances from the source, using an isotropic detector within nearby needles. Penetration depth was calculated using the Boltzmann approximation to the diffusion equation. Delivery detector fiber separation was measured on computed tomography. The mean penetration depth was 0.57 cm, but there was within patient variation of a mean factor of 4.3. Further work is ongoing to assess the effect of such variability in light penetration, on the PDT effect.     

Photodynamic dose does not correlate with long-term tumor response to mTHPC-PDT performed at several drug-light intervals

Meso-tetra-hydroxyphenyl-chlorin (mTHPC, Foscan), a promising photosensitizer for photodynamic therapy (PDT), is approved in Europe for the palliative treatment of head and neck cancer. Based on work in mice that investigated optimal tumor accumulation, clinical protocols with Foscan typically employ an interval of 96 h between systemic sensitizer administration and irradiation. However, recent studies in mouse tumor models have demonstrated significantly improved long-term tumor response when irradiation is performed at shorter drug-light intervals of 3 and 6 h. Using a previously published theoretical model of microscopic PDT dosimetry and informed by experimentally determined photophysical properties and intratumor sensitizer concentrations and distributions, we calculated photodynamic dose depositions following mTHPC-PDT for drug-light intervals of 3, 6, 24, and 96 h. Our results demonstrate that the singlet oxygen dose to the tumor volume does not track even qualitatively with tumor responses for these four drug-light intervals. Further, microscopic analysis of simulated singlet oxygen deposition shows that in no case do any subpopulations of tumor cells receive a threshold dose. Indeed, under the conditions of these simulations more than 90% of the tumor volume receives a dose that is approximately 20-fold lower than the threshold dose for mTHPC. Thus, in this evaluation of mTHPC-PDT at various drug-light intervals, any PDT dose metric that is proportional to singlet oxygen creation and/or deposition would fail to predict the tumor response. In situations like this one, other reporters of biological response to therapy would be necessary.     

Near-infrared light induced in vivo photodynamic therapy of cancer based on upconversion nanoparticles

Upconversion nanoparticles (UCNPs) that emit high-energy photons upon excitation by the low-energy near-infrared (NIR) light are emerging as new optical nano-probes useful in biomedicine. Herein, we load Chlorin e6 (Ce6), a photosensitizer, on polymer-coated UCNPs, forming a UCNP-Ce6 supramolecular complex that produces singlet oxygen to kill cancer cells under NIR light. Excellent photodynamic therapy (PDT) efficacy is achieved in tumor-bearing mice upon intratumoral injection of UCNP-Ce6 and the followed NIR light exposure. It is further uncovered that UCNPs after PDT treatment are gradually cleared out from mouse organs, without rendering appreciable toxicity to the treated animals. Moreover, we demonstrate that the NIR-induced PDT based on UCNP-Ce6 exhibits a remarkably increased tissue penetration depth compared to the traditional PDT using visible excitation light, offering significantly improved treatment efficacy for tumors blocked by thick biological tissues. Our work demonstrates NIR light-induced in vivo PDT treatment of cancer in animals, and highlights the promise of UCNPs for multifunctional in vivo cancer treatment and imaging.     

Immune response against angiosarcoma following lower fluence rate clinical photodynamic therapy.

Tumor response to photodynamic therapy (PDT) is dependent on treatment parameters used. In particular, the light fluence rate may be an important determinant of the treatment outcome. In this clinical case report, we describe the response of angiosarcoma to PDT carried out using different fluence rates and drug and light doses. A patient with recurrent multifocal angiosarcoma of the head and neck was recruited for PDT. A new generation chlorin-based photosensitizer, Fotolon, was administered at a dose of 2.0 to 5.7 mg/kg. The lesions were irradiated with 665 nm laser light for a light dose of 65 to 200 J/cm2 delivered at a fluence rate of 80 or 150 mW/cm2. High dose PDT carried out at a high fluence rate resulted in local control of the disease for up to a year; however, the disease recurred and PDT had to be repeated. PDT of new lesions carried out at a lower fluence rate resulted in tumor eradication. More significantly, it also resulted in spontaneous remission of neighboring and distant untreated lesions. Repeat PDT carried out on a recurrent lesion at a lower fluence rate resulted in eradication of both treated and untreated lesions despite the lower total light dose delivered. Immunohistochemical examination of biopsy samples implies that PDT could have activated a cell-mediated immune response against untreated lesions. Subsequent histopathological examination of the lesion sites showed negative for disease. Our clinical observations show that lower fluence rate PDT results in better outcome and also indicate that the fluence rate, rather than the total light dose, is a more crucial determinant of the treatment outcome. Specifically, lower fluence rate PDT appears to activate the body's immune response against untreated lesions.     

Real-time optoacoustic monitoring of vascular damage during photodynamic therapy treatment of tumor

The optoacoustic technique is a noninvasive imaging method with high spatial resolution. It potentially can be used to monitor anatomical and physiological changes. Photodynamic therapy (PDT)-induced vascular damage is one of the important mechanisms of tumor destruction, and real-time monitoring of vascular changes can have therapeutic significance. A unique optoacoustic system is developed for neovascular imaging during tumor phototherapy. In this system, a single-pulse laser beam is used as the light source for both PDT and for concurrently generating ultrasound signals for optoacoustic imaging. To demonstrate its feasibility, this system is used to observe vascular changes during PDT treatment of chicken chorioallantoic membrane (CAM) tumors. The photosensitizer used in this study is protoporphyrin IX (PpIX) and the laser wavelength is 532 nm. Neovascularization in tumor angiogenesis is visualized by a series of optoacoustic images at different stages of tumor growth. Damage of the vascular structures by PDT is imaged before, during, and after treatment. Rapid, real-time determination of the size of targeted tumor blood vessels is achieved, using the time difference of positive and negative ultrasound peaks during the PDT treatment. The vascular effects of different PDT doses are also studied. The experimental results show that a pulsed laser can be conveniently used to hybridize PDT treatment and optoacoustic imaging and that this integrated system is capable of quantitatively monitoring the structural change of blood vessels during PDT. This method could be potentially used to guide PDT and other phototherapies using vascular changes during treatment to optimize treatment protocols, by choosing appropriate types and doses of photosensitizers and doses of light.     

Comparison of merocyanine 540-mediated photodynamic action on leukemia cells between pulsed and continuous wave light sources.

Whether a pulsed laser is superior to a continuous wave (CW) light source in photodynamic therapy (PDT) of cancer is still unclear and contradictory in the literature. Although photosaturation of a sensitizer and oxygen depletion in tumor have been considered to be involved during pulsed laser irradiation, there is a lack of experimental data. In the present work several parameters such as the amount of merocyanine 540 (MC540) in cells, the oxygen concentration in cells, and the amount of photos reaching cells during pulsed laser irradiation, were studied to compare the MC540-mediated PDT effects of a pulsed laser and a CW light source on murine myeloid WEH-3B (JCS) cells in vitro. The results showed that the pulsed laser was less effective at cell inactivation than the CW light under the same irradiation dose. However, when the energy of the pulsed laser was reduced from 0.25 to 0.06 mJ/cm2 while keeping the total irradiation dose unchanged, the photoinactivation of cells was increased significantly. Based on the measurements and calculations for the present experimental conditions, each cell has about 108 MC540 molecules bound (5 microg/ml MC540 for 1 hr) and receives about 109 photos from 0.25 mJ/cm2 of the pulsed laser. The results indicate that the photosaturation of MC540 occurs in the present conditions due to the fact that the photons received by one cell in one laser pulse were much more than the numbers of MC540 molecules bound to one cell. Thus, the photosaturation of the photosensitizer is one of the reasons to explain the different efficiency in cell inactivation between the pulsed laser and CW light.     

Optimization of light source parameters in the photodynamic therapy of heterogeneous prostate

The three-dimensional (3D) heterogeneous distributions of optical properties in a patient prostate can now be measured in vivo. Such data can be used to obtain a more accurate light-fluence kernel. (For specified sources and points, the kernel gives the fluence delivered to a point by a source of unit strength.) In turn, the kernel can be used to solve the inverse problem that determines the source strengths needed to deliver a prescribed photodynamic therapy (PDT) dose (or light-fluence) distribution within the prostate (assuming uniform drug concentration). We have developed and tested computational procedures to use the new heterogeneous data to optimize delivered light-fluence. New problems arise, however, in quickly obtaining an accurate kernel following the insertion of interstitial light sources and data acquisition. (1) The light-fluence kernel must be calculated in 3D and separately for each light source, which increases kernel size. (2) An accurate kernel for light scattering in a heterogeneous medium requires ray tracing and volume partitioning, thus significant calculation time. To address these problems, two different kernels were examined and compared for speed of creation and accuracy of dose. Kernels derived more quickly involve simpler algorithms. Our goal is to achieve optimal dose planning with patient-specific heterogeneous optical data applied through accurate kernels, all within clinical times. The optimization process is restricted to accepting the given (interstitially inserted) sources, and determining the best source strengths with which to obtain a prescribed dose. The Cimmino feasibility algorithm is used for this purpose. The dose distribution and source weights obtained for each kernel are analyzed. In clinical use, optimization will also be performed prior to source insertion to obtain initial source positions, source lengths and source weights, but with the assumption of homogeneous optical properties. For this reason, we compare the results from heterogeneous optical data with those obtained from average homogeneous optical properties. The optimized treatment plans are also compared with the reference clinical plan, defined as the plan with sources of equal strength, distributed regularly in space, which delivers a mean value of prescribed fluence at detector locations within the treatment region. The study suggests that comprehensive optimization of source parameters (i.e. strengths, lengths and locations) is feasible, thus allowing acceptable dose coverage in a heterogeneous prostate PDT within the time constraints of the PDT procedure.     

Near-infrared optical properties of ex vivo human uterus determined by the Monte Carlo inversion technique.

The optical properties, absorption (mua) and reduced scattering coefficient (mu's), of ex vivo human myometrium and leiomyoma (fibroid) have been determined by the Monte Carlo inversion technique over the wavelength range 600-1000 nm. This region is currently of interest for new, minimal-access, surgical laser procedures such as photodynamic therapy (PDT) for abnormalities of the uterus, and interstitial laser photocoagulation (ILP) for the thermal ablation of fibroids. In the region 630-675 nm (corresponding to PDT), the optical coefficients of myometrium are mua = 0.041+/-0.012 mm(-1) and mu's = 1.37+/-0.19 mm(-1). For the wavelength range 800-1000 nm (associated with infrared lasers for ILP), the optical coefficients of fibroid were found to be mua = 0.020+/-0.003 mm(-1) and mu's = 0.56+/-0.03 mm(-1). Overall, the optical properties of fibroid were found to be lower than myometrium, and this was attributed to the differences in both anatomy and vascularity. The results show that PDT for ablation of the uterine endometrium is most unlikely to affect any tissues beyond the myometrium, and that the region around 800 nm is the most effective for ablation of fibroids using ILP as the penetration depth of light is greatest at this wavelength.