Tom A. Middelburg

Fractionated illumination at low fluence rate photodynamic therapy in mice.

Photodynamic therapy (PDT) for actinic field cancerization is effective but painful. Pain mechanisms remain unclear but fluence rate has been shown to be a critical factor. Lower fluence rates also utilize available oxygen more efficiently. We investigated PDT effect in normal SKH1‐HR mice using low and high fluence rate aminolevulinic acid (ALA) PDT and a fractionated illumination scheme. Six groups of six mice with different light treatment parameters were studied. Visual skin damage was assessed up to 7 days post‐PDT. Fluorescence and reflectance spectroscopy during illuminations provided us with real‐time information about protoporphyrin IX (PpIX) photobleaching. A novel dosing approach was introduced in that we used a photobleaching percentage instead of a preset fluence. Data show similar total and maximum damage scores in high and low fluence rate groups. Photobleaching of PpIX in the low fluence rate groups shows a trend toward more efficient photobleaching. Results indicate that low fluence rate PDT is as effective as and more efficient than high fluence rate PDT in normal mouse skin. Low fluence rate PDT light protocols need to be explored in human studies in search for an effective and well‐tolerated treatment for actinic field cancerization.

Topical Photodynamic Therapy Using Different Porphyrin Precursors Leads to Differences in Vascular Photosensitization and Vascular Damage in Normal Mouse Skin

Different distributions of hexyl aminolevulinate (HAL), aminolevulinic acid (ALA) and methyl aminolevulinate (MAL) in the superficial vasculature are not well studied but they are hypothesized to play an important role in topical photodynamic therapy (PDT). The colocalization of fluorescent CD31 and protoporphyrin IX (PpIX) was calculated using confocal microscopy of mouse skin sections to investigate the vascular distribution after topical application. Vascular damage leads to disruption of the normal endothelial adherens junction complex, of which CD144 is an integral component. Therefore, normal CD31 combined with loss of normal fluorescent CD144 staining was visually scored to assess vascular damage. Both the vascular PpIX concentration and the vascular damage were highest for HAL, then ALA and then MAL. Vascular damage in MAL was not different from normal contralateral control skin. This pattern is consistent with literature data on vasoconstriction after PDT, and with the hypothesis that the vasculature plays a role in light fractionation that increases efficacy for HAL and ALA‐PDT but not for MAL. These findings indicate that endothelial cells of superficial blood vessels synthesize biologically relevant PpIX concentrations, leading to vascular damage. Such vascular effects are expected to influence the oxygenation of tissue after PDT which can be important for treatment efficacy.

Topical hexylaminolevulinate and aminolevulinic acid photodynamic therapy: Complete arteriole vasoconstriction occurs frequently and depends on protoporphyrin IX concentration in vessel wall

Vascular responses to photodynamic therapy (PDT) may influence the availability of oxygen during PDT and the extent of tumor destruction after PDT. However, for topical PDT vascular effects are largely unknown. Arteriole and venule diameters were measured before and after hexylaminolevulinate (HAL) and aminolevulinic acid (ALA) PDT and related to the protoporphyrin IX (PpIX) concentration in the vessel wall. A mouse skin fold chamber model and an intravital confocal microscope allowed direct imaging of the subcutaneous vessels underlying the treated area. In both HAL and ALA groups over 60% of arterioles constricted completely, while venules generally did not respond, except for two larger veins that constricted partially. Arteriole vasoconstriction strongly correlated with PpIX fluorescence intensity in the arteriole wall. Total PpIX fluorescence intensity was significantly higher for HAL than ALA for the whole area that was imaged but not for the arteriole walls. In conclusion, complete arteriole vasoconstriction occurs frequently in both HAL and ALA based topical PDT, especially when relatively high PpIX concentrations in arteriole walls are reached. Vasoconstriction will likely influence PDT effect and should be considered in studies on topical HAL and ALA-PDT. Also, our results may redefine the vasculature as a potential secondary target for topical PDT.

Monitoring blood volume and saturation using superficial fibre optic reflectance spectroscopy during PDT of actinic keratosis

Optically monitoring the vascular physiology during photodynamic therapy (PDT) may help understand patient-specific treatment outcome. However, diffuse optical techniques have failed to observe changes herein, probably by optically sampling too deep. Therefore, we investigated using differential path-length spectroscopy (DPS) to obtain superficial measurements of vascular physiology in actinic keratosis (AK) skin. The AK-specific DPS interrogation depth was chosen up to 400 microns in depth, based on the thickness of AK histology samples. During light fractionated aminolevulinic acid-PDT, reflectance spectra were analyzed to yield quantitative estimates of blood volume and saturation. Blood volume showed significant lesion-specific changes during PDT without a general trend for all lesions and saturation remained high during PDT. This study shows that DPS allows optically monitoring the superficial blood volume and saturation during skin PDT. The patient-specific variability supports the need for dosimetric measurements. In DPS, the lesion-specific optimal interrogation depth can be varied based on lesion thickness.

Ecthyma gangrenosum caused by Pseudomonas aeruginosa in a patient with astrocytoma treated with chemotherapy

Ecthyma gangrenosum, presenting as embolic lesions caused by Pseudomonas aeruginosa infection, has distinct pathognomonic features and a high mortality rate in patients with bacteremia, but when recognized early is easily treated. In this case report we describe this disseminated infection in an adult patient treated with chemotherapy for an astrocytoma.

The effect of light fractionation with a 2-h dark interval on the efficacy of topical hexyl-aminolevulinate photodynamic therapy in normal mouse skin.

BACKGROUND Light fractionation with a 2-h dark interval increases the efficacy of topical aminolevulinic acid (ALA) photodynamic therapy (PDT). Hexyl-aminolevulinate (HAL) is the hexyl ester of ALA. Both HAL and ALA lead to protoporphyrin IX (PpIX) accumulation in endothelial cells and to vascular effects, which are important for light fractionation. We investigated light fractionation for HAL-PDT in a mouse skin model and compared this with ALA. METHODS Three illumination schemes were studied: (a) 100 J cm(-2) in a single illumination; (b) 50+50 J cm(-2) in a twofold illumination; (c) a small first light fraction until 50% of PpIX was photobleached (ca. 3 J cm(-2)), followed by 97 J cm(-2) 2h later. PpIX fluorescence was measured continuously during illumination. Efficacy was evaluated by daily visual skin damage scoring up to 7 days after PDT. RESULTS Light fractionation showed a trend towards increased efficacy for HAL-PDT. Both the initial PpIX synthesis and the PpIX resynthesis during the dark interval were higher for ALA, but these were not correlated with efficacy. Single HAL-PDT was more effective than single ALA-PDT. Photobleaching rates of HAL and ALA were similar indicating similar biodistributions at depth. CONCLUSION Our results provide evidence to support that light fractionation may be beneficial for HAL-PDT. We are cautious because we found only a non-significant increase in response. However, combining our results with literature data suggest that the illumination scheme may be further optimized for HAL-PDT to potentially enhance the effect of light fractionation.

Red light ALA-PDT for large areas of actinic keratosis is limited by severe pain and patient dissatisfaction

To the Editor, Treatment of actinic keratosis field cancerization poses an increasing challenge to the dermatologist. Photodynamic therapy (PDT) using aminolevulinic acid (ALA) or its methyl ester is an attractive treatment modality for this indication because it is an effective, single-day procedure with excellent cosmetic results. The main disadvantage of PDT is that it can be painful, limiting its applicability. Many factors influencing pain have been described in the literature: PpIX concentration; fluence rate; wavelength; treatment area size; localization; use of ALA or its methyl ester; sex; skin type; lesion redness; age; and lesion type (1–6), but results are inconsistent. Moreover, an important consideration is that the outcomes are often difficult to interpret clinically. Pain is typically measured using a visual analogue scale (VAS). One approach has been to identify risk factors for pain using linear regression, resulting in beta coefficients that predict higher VAS scores. Another approach has been to compare the mean VAS score between two randomized groups. Both the beta coefficients and the magnitude of the mean difference can be difficult to interpret, due to the nonlinear nature of the VAS score, and may not represent a clinically relevant association or difference. Therefore, in this prospective study we chose severe vs. non-severe pain as binary outcome, which is clinically relevant and easy to understand. In addition, patient satisfaction was studied, which is becoming an increasingly important endpoint of clinical studies but which is not well studied in PDT. Our aim was to identify risk factors for severe pain, measure patient satisfaction and investigate the influence of severe pain on satisfaction. The study was approved by the local ethical committee, is in accordance with the declaration of Helsinki and all patients gave written informed consent prior to inclusion. We included 48 patients that were treated with fractionated ALA-PDT for actinic field cancerization of at least 25 cm in the face, scalp or back of hands. The light fractionated treatment protocol is the standard treatment in our university hospital. It involves delivery of 20 J cm−2 in the first illumination after 4 hours of 20% ALA gel application under occlusion, followed by a dark interval of two hours and delivery of an additional 80 J/cm in a second illumination. We used a Waldmann PDT 1200 L lamp (Herbert Waldmann GmbH, Villingen-Schwenningen, Germany), with an emission peak around 635 nm and a spectrum of 600–730 nm. The following characteristics were collected: age (older or younger than the mean), sex (m/f), hair colour (red/other), skin type (I-III) and the size of the treatment area (divided into three equal categories Photodermatology, Photoimmunology & Photomedicine

Fractionated PDT with 5-aminolevulinic acid: effective, cost effective and patient friendly

PDT with ALA and MAL is established as a relatively effective treatment for non-melanoma skin cancer and premalignancies. PDT is often repeated, because a single treatment gives poor long term results. Preclinical studies showed that ALA-PDT applying a fractionated illumination scheme with a small first light fraction and a second larger light fraction separated by a dark interval of two hours resulted in a significant increase in efficacy. Whereas the efficacy was not enhanced by fractionating MAL-PDT, indicating that ALA-PDT mechanism is not the same as MAL-PDT mechanism. The increase in efficacy using fractionated PDT was confirmed clinically. A randomized comparative clinical study comparing fractionated ALA-PDT versus non-fractionated ALA-PDT in the treatment of superficial basal cell carcinoma showed a significant higher response rate in the lesions treated with fractionated ALA-PDT after a follow-up of one year ( p<0.002, log-rank test). The five year follow-up is studied at moment. So far the complete response in the group treated with fractionated ALA-PDT seems to be only a few percentages lower compared to the one year follow-up. Besides the gain in response rate, fractionated ALA PDT is cost effective. ALA gel is less expensive than the commercially available MAL (Metvix) and moreover fractionated ALA-PDT takes one treatment day, instead of two treatment days using the Metvix treatment protocol (two MAL-PDT treatments separated by one week), both reducing direct and indirect costs and the burden to the patient.

Correction of fluorescence for depth-specific optical and vascular properties using reflectance and differential path-length spectroscopy during PDT

Introduction: The rate of PpIX fluorescence photobleaching is routinely used as a dose metric for ALA-PDT. Diffuse reflection spectroscopy is often used to account for variations in tissue optical properties at the photosensitizer excitation and emission bands. It can be used to quantify changes in vascular parameters, such as blood volume fraction and saturation, and can aid understanding of tissue response to PDT. The volume and(/or) depth over which these signals are acquired are critical. The aim of this study is to use quantitative reflectance spectroscopy (DPS) to correct fluorescence for changes in tissue optical properties and monitor PDT. Materials & Methods: ALA was topically applied to hairless mice skin and the incubated spot was treated with PDT according to fractionated illumination schemes. DPS measurements of vascular parameters and optical properties were performed directly before and after illumination. Both the differential signal, delivery-and-collection-fiber signal and the collection fiber signal, which all probe different measurement volumes, are analyzed. Results & Conclusions: Analysis of DPS measurements shows that at the depth where most fluorescence originates, there is almost no blood present. During PDT vascular parameters at this depth stay constant. In more oxygenated layers of the tissue, the optical properties do change during PDT, suggesting that only a small part of PpIX fluorescence originates from the interesting depths where vascular response occurs. Correcting fluorescence emission spectra for optical changes at specific depths and not for the total of changes in a larger volume, as is usually done now, can improve PpIX photobleaching based treatment monitoring.