Quantitative and qualitative 5-aminolevulinic acid-induced protoporphyrin IX fluorescence in skull base meningiomas

Pharmaceutical equivalent 5-aminolevulinic acid fluorescence guided resection of central nervous system tumors: feasibility, safeness and cost-benefit considerations

PURPOSE

5-aminolevulinic acid (5-ALA) fluorescence-guided resection (FGR) has been an essential tool in the 'standard of care' of malignant gliomas. Over the last two decades, its indications have been extended to other neoplasms, such as metastases and meningiomas. However, its availability and cost-benefit still pose a challenge for widespread use. The present article reports a retrospective series of 707 cases of central nervous system (CNS) tumors submitted to FGR with pharmacological equivalent 5-ALA and discusses financial implications, feasibility and safeness.

METHODS

From December 2015 to February 2024, a retrospective single institution series of 707 cases of 5-ALA FGR were analyzed. Age, gender, 5-ALA dosage, intraoperative fluorescence finding, diagnosis and adverse effects were recorded. Financial impact in the surgical treatment cost were also reported.

RESULTS

there was an additional cost estimated in $300 dollars for each case, increasing from 2,37 to 3,28% of the total hospitalization cost. There were 19 (2,69%) cases of asymptomatic photosensitive reaction and 2 (0,28%) cases of photosensitive reaction requiring symptomatic treatment. 1 (0,14%) patient had a cutaneous rash sustained for up to 10 days. No other complications related to the method were evident. In 3 (0,42%) cases of patients with intracranial hypertension, there was vomiting after administration.

CONCLUSION

FGR with pharmacological equivalent 5-ALA can be considered safe and efficient and incorporates a small increase in hospital expenses. It constitutes a reliable solution in avoiding prohibitive costs worldwide, especially in countries where commercial 5-ALA is unavailable.

Topographic Patterns of Intracranial Meningioma Recurrences-Systematic Review with Clinical Implication

BACKGROUND

While several risk factors for recurrences have been defined, the topographic pattern of meningioma recurrences after surgical resection has been scarcely investigated. The possibility of theoretically predicting the site of recurrence not only allows us to better understand the pathogenetic bases of the disease and consequently to drive the development of new targeted therapies, but also guides the decision-making process for treatment strategies and tailored follow-ups to decrease/prevent recurrence.

METHODS

The authors performed a comprehensive and detailed systematic literature review of the EMBASE and MEDLINE electronic online databases regarding the topographic pattern of recurrence after surgical treatment for intracranial meningiomas. Demographics and histopathological, neuroradiological and treatment data, pertinent to the topography of recurrences, as well as time to recurrences, were extracted and analyzed.

RESULTS

Four studies, including 164 cases of recurrences according to the inclusion criteria, were identified. All studies consider the possibility of recurrence at the previous dural site; three out of four, which are the most recent, consider 1 cm outside the previous dural margin to be the main limit to distinguish recurrences closer to the previous site from those more distant. Recurrences mainly occur within or close to the surgical bed; higher values of proliferation index are associated with recurrences close to the original site rather than within it.

CONCLUSIONS

Further studies, including genomic characterization of different patterns of recurrence, will better clarify the main features affecting the topography of recurrences. A comparison between topographic classifications of intracranial meningioma recurrences after surgery and after radiation treatment could provide further interesting information.

5-ALA induced PpIX fluorescence spectroscopy in neurosurgery: a review

The review begins with an overview of the fundamental principles/physics underlying light, fluorescence, and other light-matter interactions in biological tissues. It then focuses on 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence spectroscopy methods used in neurosurgery (e.g., intensity, time-resolved) and in so doing, describe their specific features (e.g., hardware requirements, main processing methods) as well as their strengths and limitations. Finally, we review current clinical applications and future directions of 5-ALA-induced protoporphyrin IX (PpIX) fluorescence spectroscopy in neurosurgery.

A birefringent spectral demultiplexer enables fast hyper-spectral imaging of protoporphyrin IX during neurosurgery

Hyperspectral imaging and spectral analysis quantifies fluorophore concentration during fluorescence-guided surgery1-6. However, acquisition of the multiple wavelengths required to implement these methods can be time-consuming and hinder surgical workflow. To this end, a snapshot hyperspectral imaging system capable of acquiring 64 channels of spectral data simultaneously was developed for rapid hyperspectral imaging during neurosurgery. The system uses a birefringent spectral demultiplexer to split incoming light and redirect wavelengths to different sections of a large format microscope sensor. Its configuration achieves high optical throughput, accepts unpolarized input light and exceeds channel count of prior image-replicating imaging spectrometers by 4-fold. Tissue-simulating phantoms consisting of serial dilutions of the fluorescent agent characterize system linearity and sensitivity, and comparisons to performance of a liquid crystal tunable filter based hyperspectral imaging device are favorable. The new instrument showed comparable, if not improved, sensitivity at low fluorophore concentrations; yet, acquired wide-field images at more than 70-fold increase in frame rate. Image data acquired in the operating room during human brain tumor resection confirm these findings. The new device is an important advance in achieving real-time quantitative imaging of fluorophore concentration for guiding surgery.

Influence of dexamethasone on visible 5-ALA fluorescence and quantitative protoporphyrin IX accumulation measured by fluorescence lifetime imaging in glioblastomas: is pretreatment obligatory before fluorescence-guided surgery?

OBJECTIVE

Fluorescence-guided surgery using 5-aminolevulinic acid (5-ALA) is nowadays widely applied for improved resection of glioblastomas (GBMs). Initially, pretreatment with dexamethasone was considered to be essential for optimal fluorescence effect. However, recent studies reported comparably high rates of visible fluorescence in GBMs despite absence of dexamethasone pretreatment. Recently, the authors proposed fluorescence lifetime imaging (FLIM) for the quantitative analysis of 5-ALA-induced protoporphyrin IX (PpIX) accumulation. The aim of this study was thus to investigate the influence of dexamethasone on visible fluorescence and quantitative PpIX accumulation.

METHODS

The authors prospectively analyzed the presence of visible fluorescence during surgery in a cohort of patients with GBMs. In this study, patients received dexamethasone preoperatively only if clinically indicated. One representative tumor sample was collected from each GBM, and PpIX accumulation was analyzed ex vivo by FLIM. The visible fluorescence status and mean FLIM values were correlated with preoperative intake of dexamethasone.

RESULTS

In total, two subgroups with (n = 27) and without (n = 20) pretreatment with dexamethasone were analyzed. All patients showed visible fluorescence independent from preoperative dexamethasone intake. Furthermore, the authors did not find a statistically significant difference in the mean FLIM values between patients with and without dexamethasone pretreatment (p = 0.097).

CONCLUSIONS

In this first study to date, the authors found no significant influence of dexamethasone pretreatment on either visible 5-ALA fluorescence during GBM surgery or PpIX accumulation based on FLIM. According to these preliminary data, the authors recommend administering dexamethasone prior to fluorescence-guided surgery of GBMs only when clinically indicated.

Use of digital photography to identify neoplastic skin lesions after labelling by ALA-derived protoporphyrin

Actinic keratosis is a premalignant skin lesion that develops into non-melanoma skin cancer. Various imaging techniques have been developed to find the actinic keratosis lesion. In this clinical study, the feasibility of a nonspectroscopic fluorescence imaging system is investigated for spatial assessment of the actinic keratosis lesion. Six patients between the ages of 70 and 80 years old are diagnosed with actinic keratosis by a board-certified dermatologist to obtain biopsy-proven clinical images. The patients were treated with 5-aminolevulinic acid, which is transformed into the protoporphyrin IX. After illuminating ultraviolet-A light on facial lesions, the protoporphyrin IX produces the exogenous fluorescence. The fluorescence is measured using both a hyperspectral camera and an RGB color camera to obtain spectroscopic and nonspectroscopic fluorescence images, respectively. It is found that fluorescence intensity of the actinic keratosis lesion is higher than that of normal skin. Based on combined fluorescence and physiological characteristics, the actinic keratosis lesion is distinguished from the adjacent normal skin area. For delineation of the actinic keratosis lesion, a linear unmixing algorithm is applied to spectroscopic image data and an erythema index is calculated from nonspectroscopic image data. Then, two extracted actinic keratosis lesions are compared for cross-validation. As a result, both spectroscopic and nonspectroscopic fluorescence images demarcate an identical lesion of actinic keratosis. Given the affordability and simplicity, an RGB camera and a 5-ALA photosensitizer can be used as a cost-effective nonspectroscopic imaging modality for accurate assessment of actinic keratosis margins.

5-Aminolevulinic Acid-Induced Fluorescence in Focal Cortical Dysplasia: Report of 3 Cases

BACKGROUND

Three patients enrolled in a clinical trial of 5-aminolevulinic-acid (5-ALA)-induced fluorescence-guidance, which has been demonstrated to facilitate intracranial tumor resection, were found on neuropathological examination to have focal cortical dysplasia (FCD).

OBJECTIVE

To evaluate in this case series visible fluorescence and quantitative levels of protoporphyrin IX (PpIX) during surgery and correlate these findings with preoperative magnetic resonance imaging (MRI) and histopathology.

METHODS

Patients were administered 5-ALA (20 mg/kg) approximately 3 h prior to surgery and underwent image-guided, microsurgical resection of their MRI- and electrophysiologically identified lesions. Intraoperative visible fluorescence was evaluated using an operating microscope adapted with a commercially available blue light module. Quantitative PpIX levels were assessed using a handheld fiber-optic probe and a wide-field imaging spectrometer. Sites of fluorescence measurements were co-registered with both preoperative MRI and histopathological analysis.

RESULTS

Three patients with a pathologically confirmed diagnosis of FCD (Types 1b, 2a, and 2b) underwent surgery. All patients demonstrated some degree of visible fluorescence (faint or moderate), and all patients had quantitatively elevated concentrations of PpIX. No evidence of neoplasia was identified on histopathology, and in 1 patient, the highest concentrations of PpIX were found at a tissue site with marked gliosis but no typical histological features of FCD.

CONCLUSION

FCD has been found to be associated with intraoperative 5-ALA-induced visible fluorescence and quantitatively confirmed elevated concentrations of the fluorophore PpIX in 3 patients. This finding suggests that there may be a role for fluorescence-guidance during surgical intervention for epilepsy-associated FCD.

Utility of Photodynamic Therapy in Dentistry: Current Concepts

The significant growth in scientific and technological advancements within the field of dentistry has resulted in a wide range of novel treatment modalities for dentists to use. Photodynamic therapy (PDT) is an emerging, non-invasive treatment method, involving photosensitizers, light of a specific wavelength and the generation of singlet oxygen and reactive oxygen species (ROS) to eliminate unwanted eukaryotic cells (e.g., malignancies in the oral cavity) or pathogenic microorganisms. The aim of this review article is to summarize the history, general concepts, advantages and disadvantages of PDT and to provide examples for current indications of PDT in various subspecialties of dentistry (oral and maxillofacial surgery, oral medicine, endodontics, preventive dentistry, periodontology and implantology), in addition to presenting some images from our own experiences about the clinical success with PDT.

High Interobserver Agreement in the Subjective Classification of 5-Aminolevulinic Acid Fluorescence Levels in Newly Diagnosed Glioblastomas

BACKGROUND AND OBJECTIVES

Fluorescence-guided resection of glioblastomas (GBM) using 5-aminolevulinic acid (5-ALA) improves intraoperative tumor visualization and is thus widely used nowadays. During resection, different fluorescence levels can usually be distinguished within the same tumor. Recently, we demonstrated that strong, vague, and no fluorescence correspond to distinct histopathological characteristics in newly diagnosed GBM. However, the qualitative fluorescence classification by the neurosurgeon is subjective and currently no comprehensive data on interobserver variability is available. The aim of this study was thus to investigate the interobserver variability in the classification of 5-ALA fluorescence levels in newly diagnosed GBM.

STUDY DESIGN/MATERIALS AND METHODS

A questionnaire investigating the interobserver variability in 5-ALA fluorescence quantification was performed at a nation-wide neurosurgical oncology meeting. The participants involved in the neurosurgical/neurooncological field were asked to categorize 30 cases of 5-ALA fluorescence images derived from GBM resection on a lecture hall screen according to the widely used three-tier fluorescence classification scheme (negative, vague, or strong fluorescence). Additionally, participants were asked for information on their medical background such as specialty, level of training, and experience with 5-ALA fluorescence-guided procedures. Interobserver agreement was defined as the calculated mean κ values for each observer.

RESULTS

A total of 36 questionnaires were included in the final analysis. The mean average κ value in fluorescence classification within the entire cohort was 0.71 ± 0.12 and 29 (81%) participants had a substantial or almost perfect interobserver agreement (κ values 0.6-1.0). Interobserver agreement was significantly higher in neurosurgeons (mean κ: 0.83) as compared with non-neurosurgeons involved in the neurooncological field (mean κ: 0.52; P < 0.001). Furthermore, interobserver agreement was significantly higher in participants who had experience with at least 25 5-ALA fluorescence-guided surgeries (mean κ: 0.87) compared with less experienced colleagues (mean κ: 0.82; P = 0.039).

CONCLUSION

Our study found a high interobserver agreement in the qualitative classification of different 5-ALA fluorescence levels in newly diagnosed GBM. Interobserver agreement increases significantly in more experienced participants and therefore a high level of experience is crucial for reliable intraoperative fluorescence classification. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals, Inc.

The application of fluorescence techniques in meningioma surgery-a review

Surgical resections of meningiomas, the most common intracranial tumor in adults, can only be curative if radical resection is achieved. Potentially, the extent of resection could be improved, especially in complex and/or high-grade meningiomas by fluorescence-guided surgery using 5-aminolevulinic acid (5-ALA), indocyanine green (ICG), or fluorescein. This review aims to summarize and evaluate these fluorescence-guided meningioma surgery techniques. PubMed and Embase were searched for relevant articles. Additionally, we checked reference lists for further studies. Forty-eight articles were included in the final analysis. 5-ALA fluoresced with varying sensitivity and selectivity in meningiomas and in invaded bone and dura mater. Although ICG was mainly applied for video angiography, one report shows tumor fluorescence 18-28 h post-ICG injection. Lastly, the use of fluorescein could aid in the identification of tumor remnants; however, detection of dural tail is highly questionable. Fluorescence-guided meningioma surgery should be a reliable, highly specific, and sensitive technique. Despite numerous studies reporting the use of fluorescent dyes, currently, there is no evidence that these tools improve the radical resection rate and long-term recurrence-free outcome in meningioma surgery without neurological deficits. Evidence regarding the effectiveness and increased safety of resection after the application of these fluorophores is currently lacking. Future research should focus on the development of a meningioma-targeted, highly sensitive, and specific fluorophore.

Review of clinical trials in intraoperative molecular imaging during cancer surgery

Most solid cancers are treated by surgical resections to reduce the burden of disease. Surgeons often face the challenge of detecting small areas of residual neoplasm after resection or finding small primary tumors for the initial resection. Intraoperative molecular imaging (IMI) is an emerging technology with the potential to dramatically improve cancer surgery operations by allowing surgeons to better visualize areas of neoplasm using fluorescence imaging. Over the last two years, two molecular optical contrast agents received U.S. Food and Drug Administration approval, and several more drugs are now on the horizon. Thus a conference was organized at the University of Pennsylvania to bring together oncologic surgeons from different specialties to discuss the current clinical status of IMI trials with a specific focus on phase 2 and phase 3 studies. In addition, phase 1 and experimental trials were also discussed briefly, to highlight other novel techniques. Our review summarizes the discussions from the conference and delves into the types of cancers discussed, different contrast agents in human trials, and the clinical value being studied.

5-ALA fluorescence on tumors different from malignant gliomas. Review of the literature and our experience

INTRODUCTION

Fluorescence guided surgery with 5-aminolevulinic acid (5-ALA) is a well-established technique for improving resection of malignant cerebral glioma. In recent years, this technique is being increasingly applied off label to other brain tumor entities such as Low-grade glioma, meningioma, metastases, lymphoma and other central nervous system tumors. In this paper We collected all the data of 5-ALA guided surgery in "not malignant glioma" in literature compared to our experience.

EVIDENCE ACQUISITION

We searched the PubMed/Medline database all clinical series reporting 5-ALA guided-surgery in not malignant glioma. We reviewed all data also showing our experience.

EVIDENCE SYNTHESIS

Fluorescence guided surgery with 5-ALA might be helpful not only in high-grade glioma but also in other brain tumor especially in Low grade glioma with a suspect of anaplastic spot, meningioma with bone invasion or parenchymal infiltration, ependymoma, lymphoma and pediatric tumors.

CONCLUSIONS

Due to the relatively few number or clinical studies, prospective clinical trials are needed to increase the overall level of evidence concerning the usage of 5-ALA in CNS tumors different from high-grade glioma. Furthermore, a greater us of new tools such as, spectroscopy or confocal microscope or the use of combination of other fluorescence could make more effective this technique.

[Intraoperative fluorescence diagnostics in surgery of intracranial meningiomas: analysis of 101 cases]

Fluorescence diagnostics has been extensively applied in surgery of malignant brain gliomas. However, the use of this technique in surgery of intracranial meningiomas has remained controversial.

OBJECTIVE

The study objective was to assess the sensitivity of 5-aminolevulinic acid-based (5-ALA) fluorescence diagnostics in surgery of brain meningiomas and to clarify the clinical and biological factors that may influence the fluorescent effect.

MATERIAL AND METHODS

The study consistently included 101 patients with intracranial meningiomas of various locations who were operated on using 5-ALA. There were 28 (27.72%) males and 73 (72.27%) females (median age, 54 years). In all patients, surgery was performed using an operating microscope equipped with a fluorescent module; in 24 of these, laser spectroscopy was used. For comparison of chances to observe the fluorescent effect of 5-ALA in patients having meningiomas with different WHO histological grades (Grade I vs Grade II-III), we performed a meta-analysis that included 10 studies (the largest series) on outcomes of surgical treatment of meningiomas using intraoperative fluorescence diagnostics.

RESULTS

Of 101 patients included in this series, observable fluorescence was detected in 95 (94.1%) patients: weak fluorescence in 12 (11.9%), moderate fluorescence in 23 (22.8%) cases, and strong fluorescence in 60 (59.4%) patients. There was no statistically significant relationship (p>0.05) between the rate and intensity of observable fluorescence and the tumor growth pattern (primary/continued), location, WHO grade of malignancy, and histological subtype. In the absence of intraoperative bleeding, tumor fluorescence was statistically significantly brighter (p=0.02). Of 26 patients with hyperostosis, bone fluorescence was observed in 11 (42.3%) cases. There was no statistically significant relationship between administration of dexamethasone, its dose, administration of anticonvulsants, gastrointestinal tract diseases, as well as diabetes mellitus and the fluorescence intensity. There was also no significant relationship between the extent of tumor resection (Simpson scale) and the presence of fluorescence as well as its intensity. Comparison of the observable fluorescence intensity and the laser spectroscopy indicators revealed a significant correlation (r=0.75; p=0.005).

CONCLUSION

Meningioma is a well fluorescent tumor, with the technique sensitivity being 94.1%. In some cases, the use of fluorescence diagnostics in surgery of meningiomas improves identification of residual tumor fragments and enables correction of a surgical approach. To assess the effect of fluorescence diagnostics on the recurrence rate and disease-free duration, further research is required.

Optimization of high-grade glioma resection using 5-ALA fluorescence-guided surgery: A literature review and practical recommendations from the neuro-oncology club of the French society of neurosurgery

BACKGROUND

When feasible, the surgical resection is the standard first step of the management of high-grade gliomas. 5-ALA fluorescence-guided-surgery (5-ALA-FGS) was developed to ease the intra-operative delineation of tumor borders in order to maximize the extent of resection.

METHODS

A Medline electronic database search was conducted. English language studies from January 1998 until July 2018 were included, following the PRISMA guidelines.

RESULTS

5-ALA can be considered as a specific tool for the detection of tumor remnant but has a weaker sensibility (level 2). 5-ALA-FGS is associated with a significant increase in the rate of gross total resection reaching more than 90% in some series (level 1). Consistently, 5-ALAFGS improves progression-free survival (level 1). However, the gain in overall survival is more debated. The use of 5-ALA-FGS in eloquent areas is feasible but requires simultaneous intraoperative electrophysiologic functional brain monitoring to precisely locate and preserve eloquent areas (level 2). 5-ALA is usable during the first resection of a glioma but also at recurrence (level 2). From a practical standpoint, 5-ALA is orally administered 3 hours before the induction of anesthesia, the recommended dose being 20 mg/kg. Intra-operatively, the procedure is performed as usually with a central debulking and a peripheral dissection during which the surgeon switches from white to blue light. Provided that some precautions are observed, the technique does not expose the patient to particular complications.

CONCLUSION

Although 5-ALA-FGS contributes to improve gliomas management, there are still some limitations. Future methods will be developed to improve the sensibility of 5-ALA-FGS.

Technological and Ideological Innovations in Endoscopic Skull Base Surgery

BACKGROUND

Endoscopic skull base surgery has evolved over the last several decades due to technological advances and operative techniques. Several innovations that are not yet mainstream may have significant impact on the future of endoscopic skull base surgery.

METHODS

Current literature pertaining to innovations in endoscopic skull base surgery was retrieved using PubMed, Embase, Web of Science, and Google Scholar.

RESULTS

Several recent innovations may play an influential role in the advancement of endoscopic skull base surgery, including fluorescent dyes such as indocyanine green fluorescence, fluorescein, and 5-aminolevulinic acid, 3-dimensional endoscopes, robotic surgery, and intraoperative magnetic resonance imaging.

CONCLUSIONS

Several technologies are under current investigation with the hope to improve future outcomes in endoscopic skull base surgery. Additional research and evolution are necessary and will require intense scrutiny before becoming standard of care.

5-aminolevulinic acid induced protoporphyrin IX (ALA-PpIX) fluorescence guidance in meningioma surgery

INTRODUCTION

5-aminolevulinic acid induced protoporphyrin IX (5-ALA-PpIX) fluorescence guidance has emerged as a valuable surgical adjunct for resection of intracranial tumors.

METHODS

Here we present a focused review on 5-ALA-PpIX fluorescence guidance for meningiomas.

RESULTS

We discuss the clinical studies and specific applications to date as well as the two main intraoperative fluorescence technologies applied to meningiomas.

CONCLUSIONS

The use of 5-ALA-PpIX in meningiomas holds promising potential so neurosurgeons can improve surgical outcomes for patients with meningiomas as well as be pioneers in developing improved fluorescence imaging technologies.

Surgery of Small Anterior Skull Base Meningiomas by Endoscopic 5-Aminolevulinic Acid Fluorescence Guidance: First Clinical Experience

BACKGROUND

Minimally invasive surgery of small skull base meningiomas is technically challenging. We report the role of endoscopic 5-aminolevulinic acid fluorescence guidance (e-5-ALA-FGS) for small and deep-seated anterior skull base meningiomas.

METHODS

We report the cases of 2 patients. The first case was a small olfactory groove meningioma resected via a trans-eyebrow, subfrontal approach. The second case was a clinoid meningioma with invasion of the optic canal resected via a small frontolateral approach. Intraoperative documentation demonstrated the usefulness of 5-ALA endoscopy. In either case, residual fluorescing tumor tissue was detected. No complication was encountered. The clinical and radiological outcomes were good. No regrowth had occurred after 54 and 17 months of follow-up, respectively.

RESULTS

Residual meningioma tissue on the far side of a keyhole approach (e.g., in the olfactory groove or at the optic canal) can be difficult to visualize. Visualization can be improved by use of an endoscope. To date, fluorescence guidance with a microscope was limited by insufficient fluorescence signals in deep corridors. With a specially equipped 5-ALA fluorescence endoscope, one can combine the advantages of both endoscopic vision and fluorescence guidance. The results of present report have demonstrated the usefulness of 5-ALA endoscopy for difficult to visualize areas.

CONCLUSION

Endoscopic 5-ALA fluorescence guidance was shown to be feasible when resecting small and deep-seated skull base meningiomas via minimally invasive approaches. Based on this proof of principle, we encourage its evaluation for the middle or posterior fossa (e.g., internal auditory canal) and other difficult areas (e.g., behind neurovascular structures or the brainstem). The sensitivity and specificity of this method should be prospectively and systematically investigated.

Fluorescence-guided surgery and intervention - An AAPM emerging technology blue paper

Fluorescence-guided surgery (FGS) and other interventions are rapidly evolving as a class of technologically driven interventional approaches in which many surgical specialties visualize fluorescent molecular tracers or biomarkers through associated cameras or oculars to guide clinical decisions on pathological lesion detection and excision/ablation. The technology has been commercialized for some specific applications, but also presents technical challenges unique to optical imaging that could confound the utility of some interventional procedures where real-time decisions must be made. Accordingly, the AAPM has initiated the publication of this Blue Paper of The Emerging Technology Working Group (TETAWG) and the creation of a Task Group from the Therapy Physics Committee within the Treatment Delivery Subcommittee. In describing the relevant issues, this document outlines the key parameters, stakeholders, impacts, and outcomes of clinical FGS technology and its applications. The presentation is not intended to be conclusive, but rather to inform the field of medical physics and stimulate the discussions needed in the field with respect to a seemingly low-risk imaging technology that has high potential for significant therapeutic impact. This AAPM Task Group is working toward consensus around guidelines and standards for advancing the field safely and effectively.

Various shades of red-a systematic analysis of qualitative estimation of ALA-derived fluorescence in neurosurgery

5-Aminolevulinic acid (5-ALA)-fluorescence-guided resection is well established in many neuro-oncologic centers. Different classifications of 5-ALA-induced fluorescence have been reported. The aim of the systematic analysis was to evaluate the frequency of graduations, definitions, and designations of 5-ALA-induced fluorescence qualities. A systematic database search of PubMed was performed to identify studies reporting (1) on 5-ALA fluorescence-guided either spinal or cranial surgery, (2) on qualitative estimation and/or categorization of 5-ALA-induced fluorescence, (3) in English, and (4) were published as peer-reviewed original studies. Totally, 93 studies were identified. Different classification systems of 5-ALA-induced fluorescence were found. Over 60 % of the included studies used a dichotomized categorization of 5-ALA-induced fluorescence and 27.5 % of studies distinguished two different intensities of 5-ALA fluorescent tissue in addition to non-fluorescing tissue. More than 50 % of studies explicitly defined criteria for categorization of 5-ALA-induced fluorescence. The major limitation of the present analysis might be that it mainly comprises data from retrospective, uncontrolled, non-randomized trials. However, a precise definition of each 5-ALA-induced fluorescence quality is essential. Although dichotomized classification is the most common and simple graduation system, it may not be suitable for every clinical or scientific task. A three-level 5-ALA-induced fluorescence classification with precise definition of each fluorescence quality and their correlation with histological features would be more useful and reproducible in these cases.

Fluorescence guided resection with 5-aminolevulinic acid of a pilomyxoid astrocytoma of the third ventricle

Fluorescence-guided resection with 5-aminolevulinic acid has been shown to be useful in the resection of certain brain tumors other than high grade gliomas, facilitating the intraoperative differentiation of neoplastic tissue. The technique enables the surgeon to ensure that no tumor fragments remain, thereby achieving higher rates of complete resection. Tihan first described pilomyxoid astrocytomas in 1999. They are currently classified as grade II astrocytoma according to the WHO classification system and, because of their tendency to recur and their dissemination through the cerebrospinal fluid pathways, they are considered to be more aggressive than pilocytic astrocytoma. As a result, management of these tumors must be more aggressive, always aiming for complete macroscopic resection whenever possible. In this article, we present a case of pilomyxoid astrocytoma of the third ventricle in which the use of fluorescence-guided resection with 5-ALA facilitated complete resection. Imaging tests performed after five years revealed no signs of recurrence and no adjuvant radiotherapy or chemotherapy was required. This article also comprises a review of the literature concerning the characteristics and management of this tumor, which was recently considered to be a different histopathological entity.

Randomized, Prospective Double-Blinded Study Comparing 3 Different Doses of 5-Aminolevulinic Acid for Fluorescence-Guided Resections of Malignant Gliomas

BACKGROUND

Five-aminolevulinic acid (5-ALA) is used for fluorescence-guided resections of malignant glioma at a dose of 20 mg/kg; yet, it is unknown whether lower doses may also provide efficacy.

OBJECTIVE

To perform a double-blinded randomized study comparing 3 different doses of 5-ALA.

METHODS

Twenty-one patients with suspected malignant glioma were randomly assigned to 0.2, 2, or 20 mg/kg 5-ALA. Investigators were unaware of dose. Intraoperatively, regions of interest were first defined in tumor core, margin, and adjacent white matter under white light. Under violet-blue illumination, the surgeon's impression of fluorescence was recorded per region, followed by spectrometry and biopsy. Plasma was collected after administration and analyzed for 5-ALA and protoporphyrin IX (PPIX) content.

RESULTS

The positive predictive value of fluorescence was 100%. Visual and spectrometric fluorescence assessment showed 20 mg/kg to elicit the strongest fluorescence in tumor core and margins, which correlated with cell density. Spectrometric and visual fluorescence correlated significantly. A 10-fold increase in 5-ALA dose (2-20 mg/kg) resulted in a 4-fold increase of fluorescence contrast between marginal tumor and adjacent brain. t max for 5-ALA was 0.94 h for 20 mg/kg (0.2 kg: 0.50 h, 2 mg/kg: 0.61 h). Integrated PPIX plasma levels were 255.8 and 779.9 mcg*h/l (2 vs 20 mg/kg). Peak plasma concentrations were observed at 1.89 ± 0.71 and 7.83 ± 0.68 h (2 vs 20 mg/kg; average ± Standard Error of Mean [SEM]).

CONCLUSION

The highest visible and measurable fluorescence was yielded by 20 mg/kg. No fluorescence was elicited at 0.2 mg/kg. Increasing 5-ALA doses did not result in proportional increases in tissue fluorescence or PPIX accumulation in plasma, indicating that doses higher than 20 mg/kg will not elicit useful increases in fluorescence.

Fluorescence-guided resection of extracranial soft tissue tumour infiltration in atypical meningioma

The exact role of 5-aminolevulinic acid (5-ALA) fluorescence-guided meningioma resection is as yet unclear. Although most of the meningiomas show positive fluorescence, the influence on outcome, fluorescence heterogeneity within the tumour, the correlation between fluorescence and the proliferation rate, as well as different quantitative measurements are a matter of debate. Positive fluorescence in bone infiltrative meningiomas is well described, whereas little data exist about 5-ALA fluorescence within soft tissue infiltration. We add a case of histologically confirmed fluorescent tumour infiltration into soft tissue. A 78-year-old woman underwent resection of an atypical meningioma at the University Hospital of St. Poelten. Preoperative imaging showed tumour infiltration throughout the calvaria. 5-ALA fluorescence of the tumour as well as bone, periost and temporal muscle helped to perform a gross total resection. Histological examination showed an atypical meningioma (WHO Grade II) and gave proof of tumour infiltration of the bone and temporal muscle. With the aid of 5-ALA fluorescence, a gross total resection could be performed.

Analysis of the surgical benefits of 5-ALA-induced fluorescence in intracranial meningiomas: experience in 204 meningiomas

OBJECTIVE One of the most important causes for recurrence of intracranial meningiomas is residual tumor tissue that remains despite assumed complete resection. Recently, intraoperative visualization of meningioma tissue by 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence was reported. The aim of this study was to investigate the possible surgical benefits of PpIX fluorescence for detection of meningioma tissue. METHODS 5-ALA was administered preoperatively to 190 patients undergoing resection of 204 intracranial meningiomas. The meningiomas' PpIX fluorescence status, fluorescence quality (strong or vague), and intratumoral fluorescence homogeneity were investigated during surgery. Additionally, specific sites, including the dural tail, tumor-infiltrated bone flap, adjacent cortex, and potential satellite lesions, were analyzed for PpIX fluorescence in selected cases. RESULTS PpIX fluorescence was observed in 185 (91%) of 204 meningiomas. In the subgroup of sphenoorbital meningiomas (12 of 204 cases), the dural part showed visible PpIX fluorescence in 9 cases (75%), whereas the bony part did not show any PpIX fluorescence in 10 cases (83%). Of all fluorescing meningiomas, 168 (91%) showed strong PpIX fluorescence. Typically, most meningiomas demonstrated homogeneous fluorescence (75% of cases). No PpIX fluorescence was observed in any of the investigated 89 dural tails. In contrast, satellite lesions could be identified through PpIX fluorescence in 7 cases. Furthermore, tumor-infiltrated bone flaps could be visualized by PpIX fluorescence in all 13 cases. Notably, PpIX fluorescence was also present in the adjacent cortex in 20 (25%) of 80 analyzed cases. CONCLUSIONS The authors' data from this largest patient cohort to date indicate that PpIX fluorescence enables intraoperatively visualization of most intracranial meningiomas and allows identification of residual tumor tissue at specific sites. Thus, intraoperative detection of residual meningioma tissue by PpIX fluorescence might in future reduce the risk of recurrence.

Laser biospectroscopy and 5-ALA fluorescence navigation as a helpful tool in the meningioma resection

5-aminolevulinic acid (5-ALA) is a natural precursor of protoporphyrin IX (PP IX), which possesses fluorescent properties and is more intensively accumulated in tumor cells than in normal tissue. Therefore, the use of 5-ALA in the surgical treatment of intracranial tumors, particularly gliomas, has gained popularity in the last years, whereas its use in other intracranial pathological entities including meningiomas has been reported occasionally. This study describes a series of 28 patients with intracranial meningiomas, who were administered 5-ALA for a better visualization of tumor boundaries. Twelve patients underwent also laser spectroscopic analysis in order to confirm the visual impression of tumor tissue visualization. Bone infiltration was readily demonstrated. In one case, the tumor recurrence could have been prevented by removal of a tumor remnant, which would possibly have been better recognized if spectroscopic analysis had been used. Fluorescent navigation (FN) is a useful method for maximizing the radicality of meningioma surgery, particularly if the tumor infiltrates the bone, the skull base, and/or the surrounding structures.

[Clinical guidelines for the use of intraoperative fluorescence diagnosis in brain tumor surgery]

In this paper, we present a review of current literature on the application of intraoperative fluorescence diagnosis and fluorescence spectroscopy using 5-aminolevulinic acid in surgery for various types of brain tumors, both alone and in combination with other neuroimaging methods. Authors' extensive experience with these methods allowed them to develop a set of clinical guidelines for the use of intraoperative fluorescence diagnosis and fluorescence spectroscopy in surgery of brain tumors.

Intracranial Meningiomas: A 30-Year Experience and Literature Review

Intracranial meningiomas are tumors arising from the covering cells of the arachnoid layer of the dura mater or from the intraventricular choroid plexus. While mostly benign tumors, they still represent a major challenge to neurosurgeons and other medical disciplines involved in their diagnostic and therapeutic management. Although this review intends to give some state-of-the-art information from the literature, it is mainly based on personal experiences since more than 30 years caring for more than 1500 meningioma patients and point to a few new strategies to further improve on patient outcome.Diagnostics are based on magnetic resonance imaging which shows the relationship between tumor and surrounding intracranial structures, particularly the brain but also the vasculature and to some extent the cranial nerves. Furthermore, it may suggest the grading of the tumor and is very helpful in the postoperative diagnosis of complications and later follow-up course.Surgery still is the main treatment with the aim to completely remove the tumor; also in cases of recurrence, other additional options include radiotherapy and radiosurgery for incompletely removed or recurrent meningiomas. Postoperative chemotherapy has not been shown to provide substantial benefit to the patient especially in highly malignant meningiomas.All therapy options should be intended to provide the patient with the best possible functional outcome. Patients' perspective is not always equivalent to surgeons' perspectives. Neuropsychological evaluation and additional guidance of patients harboring meningiomas have proven to be important in modern neurosurgical intracranial tumor treatment. Their help beyond neurosurgical care facilitates the patients to lead an independent postoperative life.

Improved sensitivity to fluorescence for cancer detection in wide-field image-guided neurosurgery

In glioma surgery, Protoporphyrin IX (PpIX) fluorescence may identify residual tumor that could be resected while minimizing damage to normal brain. We demonstrate that improved sensitivity for wide-field spectroscopic fluorescence imaging is achieved with minimal disruption to the neurosurgical workflow using an electron-multiplying charge-coupled device (EMCCD) relative to a state-of-the-art CMOS system. In phantom experiments the EMCCD system can detect at least two orders-of-magnitude lower PpIX. Ex vivo tissue imaging on a rat glioma model demonstrates improved fluorescence contrast compared with neurosurgical fluorescence microscope technology, and the fluorescence detection is confirmed with measurements from a clinically-validated spectroscopic probe. Greater PpIX sensitivity in wide-field fluorescence imaging may improve the residual tumor detection during surgery with consequent impact on survival.

Fluorescence-guided resection with 5-aminolevulinic Acid of subependymomas of the fourth ventricle: report of 2 cases: technical case report

BACKGROUND AND IMPORTANCE

The usefulness of 5-aminolevulinic acid (5-ALA) for resection of malignant astrocytomas has been established in recent years. In addition to these tumors, it has been reported that 5-ALA fluorescence could be elicited in other tumors such as intracranial and spinal meningiomas or posterior fossa and spinal cord ependymomas, resulting in improved resections. Here, we present 2 cases of subependymomas of the fourth ventricle that showed intense fluorescence after 5-ALA administration. To the best of our knowledge, these are the first reported cases of subependymomas in this location in which 5-ALA elicited useful fluorescence.

CLINICAL PRESENTATION

Case 1 was a 61-year-old woman with a history of headaches accompanied by vomiting in the last month. Magnetic resonance imaging (MRI) revealed a tumor occupying the fourth ventricle with slight irregular enhancement. She was operated on after administration of 5-ALA. The tumor emitted intense red fluorescence when illuminated with blue light. An MRI performed 48 hours after surgery confirmed complete resection of the tumor. The pathological diagnosis was subependymoma. Case 2 was a 35-year-old man with a history of several months of headaches and vomiting. An MRI revealed a tumor occupying the caudal part of the fourth ventricle with moderate and irregular enhancement. He was operated on after administration of 5-ALA. The tumor showed intense fluorescence. An MRI performed 48 hours after surgery confirmed a complete resection of the tumor. The pathological diagnosis was subependymoma.

CONCLUSION

Fluorescence-guided resection with 5-ALA may be useful for resection of subependymomas of the fourth ventricle. However, further studies are needed.

Quantitative fluorescence using 5-aminolevulinic acid-induced protoporphyrin IX biomarker as a surgical adjunct in low-grade glioma surgery

OBJECT

Previous studies in high-grade gliomas (HGGs) have indicated that protoporphyrin IX (PpIX) accumulates in higher concentrations in tumor tissue, and, when used to guide surgery, it has enabled improved resection leading to increased progression-free survival. Despite the benefits of complete resection and the advances in fluorescence-guided surgery, few studies have investigated the use of PpIX in low-grade gliomas (LGGs). Here, the authors describe their initial experience with 5-aminolevulinic acid (ALA)-induced PpIX fluorescence in a series of patients with LGG.

METHODS

Twelve patients with presumed LGGs underwent resection of their tumors after receiving 20 mg/kg of ALA approximately 3 hours prior to surgery under an institutional review board-approved protocol. Intraoperative assessments of the resulting PpIX emissions using both qualitative, visible fluorescence and quantitative measurements of PpIX concentration were obtained from tissue locations that were subsequently biopsied and evaluated histopathologically. Mixed models for random effects and receiver operating characteristic curve analysis for diagnostic performance were performed on the fluorescence data relative to the gold-standard histopathology.

RESULTS

Five of the 12 LGGs (1 ganglioglioma, 1 oligoastrocytoma, 1 pleomorphic xanthoastrocytoma, 1 oligodendroglioma, and 1 ependymoma) demonstrated at least 1 instance of visible fluorescence during surgery. Visible fluorescence evaluated on a specimen-by-specimen basis yielded a diagnostic accuracy of 38.0% (cutoff threshold: visible fluorescence score ≥ 1, area under the curve = 0.514). Quantitative fluorescence yielded a diagnostic accuracy of 67% (for a cutoff threshold of the concentration of PpIX [CPpIX] > 0.0056 μg/ml, area under the curve = 0.66). The authors found that 45% (9/20) of nonvisibly fluorescent tumor specimens, which would have otherwise gone undetected, accumulated diagnostically significant levels of CPpIX that were detected quantitatively.

CONCLUSIONS

The authors' initial experience with ALA-induced PpIX fluorescence in LGGs concurs with other literature reports that the resulting visual fluorescence has poor diagnostic accuracy. However, the authors also found that diagnostically significant levels of CPpIX do accumulate in LGGs, and the resulting fluorescence emissions are very often below the detection threshold of current visual fluorescence imaging methods. Indeed, at least in the authors' initial experience reported here, if quantitative detection methods are deployed, the diagnostic performance of ALA-induced PpIX fluorescence in LGGs approaches the accuracy associated with visual fluorescence in HGGs.

Fluorescence-guided resection with 5-aminolevulinic acid of meningeal sarcoma in a child

BACKGROUND

The usefulness of fluorescence-guided resection with 5-aminolevulinic acid for malignant brain gliomas was demonstrated by Stummer. However, there are several articles in the literature showing the usefulness of the technique for other types of tumors, including benign tumors, such as ependymomas or meningiomas. Meningeal sarcomas are rare, highly aggressive malignant tumors, predominately affecting the pediatric population and have a poor prognosis in spite of treatment. Surgical treatment thereof should consist of the most complete resection possible.

METHODS

In this article, we present the case of a seven-year-old boy who received surgical treatment for a left frontal tumor after oral administration of 5-aminolevulinic acid (5-ALA); the definitive histological diagnosis of which was meningeal sarcoma. The technique was useful for achieving a complete resection, as the lesion emitted intense fluorescence, and after resection of the lesion with the usual technique, intraoperative fluorescent spots were observed in the resection bed that were also tumor. Imaging tests performed 5 years after surgery ruled out recurrence of the tumor.

CONCLUSION

To our knowledge, this is the first case published in the literature of meningeal sarcoma in a child in which intraoperative fluorescence with 5-ALA was used to achieve a complete resection.

Aminolevulinic acid-mediated photodynamic therapy of human meningioma: an in vitro study on primary cell lines

OBJECTIVE

Five-aminolevulinic acid (5-ALA)-induced porphyrins in malignant gliomas are potent photosensitizers. Promising results of ALA-PDT (photodynamic therapy) in recurrent glioblastomas have been published. Recently, 5-ALA-induced fluorescence was studied in meningioma surgery. Here, we present an experimental study of ALA-PDT in an in vitro model of primary meningioma cell lines.

METHODS

We processed native tumor material obtained intra-operatively within 24 h for cell culture. Epithelial membrane antigen (EMA) immunohistochemistry was performed after the first passage to confirm that cells were meningioma cells. For 5-ALA-PDT treatment, about 5000 cells per well were seeded in 20 wells of a blank 96-well plate. Each block of 4 wells was inoculated with 150 µL of 0, 25, 50 and 100 µg/mL 5-ALA solutions; one block was used as negative control without 5-ALA and without PDT. Following incubation for 3 h PDT was performed using a laser (635 nm, 18.75 J/cm²). The therapeutic response was analyzed by the water soluble tetrazolium salt (WST-1) cell viability assay 90 min after PDT.

RESULTS

5-ALA-PDT was performed in 14 primary meningioma cell lines. EMA expression was verified in 10 primary cell cultures. The remaining 4 were EMA negative and PDT was without any effect in these cultures. All 10 EMA-positive cell lines showed a significant and dose-dependent decrease in viability rate (p < 0.001). Cell survival at 5-ALA concentrations of 12.5, 25, 50 and 100 μg/mL was 96.5% ± 7.6%, 67.9% ± 29.9%, 24.0% ± 16.7% and 13.8% ± 7.5%, respectively. For the negative controls (no 5-ALA/PDT and ALA/no PDT), the viability rates were 101.72% ± 3.5% and 100.17% ± 3.6%, respectively. The LD50 for 5-ALA was estimated between 25 and 50 µg/mL.

CONCLUSION

This study reveals dose-dependent cytotoxic effects of 5-ALA-PDT on primary cell lines of meningiomas. Either 5-ALA or PDT alone did not affect cell survival. Further efforts are necessary to study the potential therapeutic effects of 5-ALA-PDT in vivo.

Fluorescence-guided surgery for brain tumors

5-aminolevulinic acid-induced protoporphyrin IX fluorescence was authorized in the EU for visualization of tumor tissue during surgery for WHO grade III and IV gliomas in 2007. It facilitates tumor identification and doubles the number of gross total resections that can be achieved in these tumors. The growing acceptance of fluorescence-guided surgery in malignant gliomas brings forward a substantial yield of data on many types of intracranial lesions. The following review summarizes the main findings of these publications and illustrates the limitations, caveats and future perspectives of 5-aminolevulinic acid-induced fluorescence in malignant glioma as well as in other brain neoplasms.

The current status of 5-ALA fluorescence-guided resection of intracranial meningiomas-a critical review

Meningiomas are the second most common primary tumors affecting the central nervous system. Surgical treatment can be curative in case of complete resection. 5-aminolevulinic acid (5-ALA) has been established as an intraoperative tool in malignant glioma surgery. A number of studies have tried to outline the merits of 5-ALA for the resection of intracranial meningiomas. In the present paper, we review the existing literature about the application of 5-ALA as an intraoperative tool for the resection of intracranial meningiomas. PubMed was used as the database for search tasks. We included articles published in English without limitations regarding publication date. Tumor fluorescence can occur in benign meningiomas (WHO grade I) as well as in WHO grade II and WHO grade III meningiomas. Most of the reviewed studies report fluorescence of the main tumor mass with high sensitivity and specificity. However, different parts of the same tumor can present with a different fluorescent pattern (heterogenic fluorescence). Quantitative probe fluorescence can be superior, especially in meningiomas with difficult anatomical accessibility. However, only one study was able to consistently correlate resected tissue with histopathological results and nonspecific fluorescence of healthy brain tissue remains a confounder. The use of 5-ALA as a tool to guide resection of intracranial meningiomas remains experimental, especially in cases with tumor recurrence. The principle of intraoperative fluorescence as a real-time method to achieve complete resection is appealing, but the usefulness of 5-ALA is questionable. 5-ALA in intracranial meningioma surgery should only be used in a protocolled prospective and long-term study.

Macroscopic optical imaging technique for wide-field estimation of fluorescence depth in optically turbid media for application in brain tumor surgical guidance

A diffuse imaging method is presented that enables wide-field estimation of the depth of fluorescent molecular markers in turbid media by quantifying the deformation of the detected fluorescence spectra due to the wavelength-dependent light attenuation by overlying tissue. This is achieved by measuring the ratio of the fluorescence at two wavelengths in combination with normalization techniques based on diffuse reflectance measurements to evaluate tissue attenuation variations for different depths. It is demonstrated that fluorescence topography can be achieved up to a 5 mm depth using a near-infrared dye with millimeter depth accuracy in turbid media having optical properties representative of normal brain tissue. Wide-field depth estimates are made using optical technology integrated onto a commercial surgical microscope, making this approach feasible for real-world applications.

In vivo visualization of GL261-luc2 mouse glioma cells by use of Alexa Fluor-labeled TRP-2 antibodies

OBJECT

For patients with glioblastoma multiforme, median survival time is approximately 14 months. Longer progression-free and overall survival times correlate with gross-total resection of tumor. The ability to identify tumor cells intraoperatively could result in an increased percentage of tumor resected and thus increased patient survival times. Available labeling methods rely on metabolic activity of tumor cells; thus, they are more robust in high-grade tumors, and their utility in low-grade tumors and metastatic tumors is not clear. The authors demonstrate intraoperative identification of tumor cells by using labeled tumor-specific antibodies.

METHODS

GL261 mouse glioma cells exhibit high expression of a membrane-bound protein called second tyrosinase-related protein (TRP-2). The authors used these cells to establish an intracranial, immunocompetent model of malignant glioma. Antibodies to TRP-2 were labeled by using Alexa Fluor 488 fluorescent dye and injected into the tail vein of albino C57BL/6 mice. After 24 hours, a craniotomy was performed and the tissue was examined in vivo by using an Optiscan 5.1 handheld portable confocal fiber-optic microscope. Tissue was examined ex vivo by using a Pascal 5 scanning confocal microscope.

RESULTS

Labeled tumor cells were visible in vivo and ex vivo under the respective microscopes.

CONCLUSIONS

Fluorescently labeled tumor-specific antibodies are capable of binding and identifying tumor cells in vivo, accurately and specifically. The development of labeled markers for the identification of brain tumors will facilitate the use of intraoperative fluorescence microscopy as a tool for increasing the extent of resection of a broad variety of intracranial tumors.

5-Aminolevulinic acid-induced protoporphyrin IX fluorescence in meningioma: qualitative and quantitative measurements in vivo

BACKGROUND

The use of 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence has shown promise as a surgical adjunct for maximizing the extent of surgical resection in gliomas. To date, the clinical utility of 5-ALA in meningiomas is not fully understood, with most descriptive studies using qualitative approaches to 5-ALA-PpIX.

OBJECTIVE

To assess the diagnostic performance of 5-ALA-PpIX fluorescence during surgical resection of meningioma.

METHODS

ALA was administered to 15 patients with meningioma undergoing PpIX fluorescence-guided surgery at our institution. At various points during the procedure, the surgeon performed qualitative, visual assessments of fluorescence by using the surgical microscope, followed by a quantitative fluorescence measurement by using an intraoperative probe. Specimens were collected at each point for subsequent neuropathological analysis. Clustered data analysis of variance was used to ascertain a difference between groups, and receiver operating characteristic analyses were performed to assess diagnostic capabilities.

RESULTS

Red-pink fluorescence was observed in 80% (12/15) of patients, with visible fluorescence generally demonstrating a strong, homogenous character. Quantitative fluorescence measured diagnostically significant PpIX concentrations (cPpIx) in both visibly and nonvisibly fluorescent tissues, with significantly higher cPpIx in both visibly fluorescent (P < .001) and tumor tissue (P = .002). Receiver operating characteristic analyses also showed diagnostic accuracies up to 90% for differentiating tumor from normal dura.

CONCLUSION

ALA-induced PpIX fluorescence guidance is a potential and promising adjunct in accurately detecting neoplastic tissue during meningioma resective surgery. These results suggest a broader reach for PpIX as a biomarker for meningiomas than was previously noted in the literature.

Quantitative monitoring of radiation induced skin toxicities in nude mice using optical biomarkers measured from diffuse optical reflectance spectroscopy

Monitoring the onset of erythema following external beam radiation therapy has the potential to offer a means of managing skin toxicities via biological targeted agents - prior to full progression. However, current skin toxicity scoring systems are subjective and provide at best a qualitative evaluation. Here, we investigate the potential of diffuse optical spectroscopy (DOS) to provide quantitative metrics for scoring skin toxicity. A DOS fiberoptic reflectance probe was used to collect white light spectra at two probing depths using two short fixed source-collector pairs with optical probing depths sensitive to the skin surface. The acquired spectra were fit to a diffusion theory model of light transport in tissue to extract optical biomarkers (hemoglobin concentration, oxygen saturation, scattering power and slope) from superficial skin layers of nude mice, which were subjected to erythema inducing doses of ionizing radiation. A statistically significant increase in oxygenated hemoglobin (p < 0.0016) was found in the skin post-irradiation - confirming previous reports. More interesting, we observed for the first time that the spectral scattering parameters, A (p = 0.026) and k (p = 0.011), were an indicator of erythema at day 6 and could potentially serve as an early detection optical biomarker of skin toxicity. Our data suggests that reflectance DOS may be employed to provide quantitative assessment of skin toxicities following curative doses of external beam radiation.

Use of fluorescence to guide resection or biopsy of primary brain tumors and brain metastases

Object

The accurate discrimination between tumor and normal tissue is crucial for determining how much to resect and therefore for the clinical outcome of patients with brain tumors. In recent years, guidance with 5-aminolevulinic acid (5-ALA)–induced intraoperative fluorescence has proven to be a useful surgical adjunct for gross-total resection of high-grade gliomas. The clinical utility of 5-ALA in resection of brain tumors other than glioblastomas has not yet been established. The authors assessed the frequency of positive 5-ALA fluorescence in a cohort of patients with primary brain tumors and metastases.

Methods

The authors conducted a single-center retrospective analysis of 531 patients with intracranial tumors treated by 5-ALA–guided resection or biopsy. They analyzed patient characteristics, preoperative and postoperative liver function test results, intraoperative tumor fluorescence, and histological data. They also screened discharge summaries for clinical adverse effects resulting from the administration of 5-ALA. Intraoperative qualitative 5-ALA fluorescence (none, mild, moderate, and strong) was documented by the surgeon and dichotomized into negative and positive fluorescence.

Results

A total of 458 cases qualified for final analysis. The highest percentage of 5-ALA–positive fluorescence in open resection was found in glioblastomas (96%, n = 99/103). Among other tumors, 5-ALA–positive fluorescence was detected in 88% (n = 21/32) of anaplastic gliomas (WHO Grade III), 40% (n = 8/19) of low-grade gliomas (WHO Grade II), no (n = 0/3) WHO Grade I gliomas, and 77% (n = 85/110) of meningiomas. Among metastases, the highest percentage of 5-ALA–positive fluorescence was detected in adenocarcinomas (48%, n = 13/27). Low rates or absence of positive fluorescence was found among pituitary adenomas (8%, n = 1/12) and schwannomas (0%, n = 0/7). Biopsies of high-grade primary brain tumors showed positive rates of fluorescence similar to those recorded for open resection. No clinical adverse effects associated with use of 5-ALA were observed. Only 1 patient had clinically silent transient elevation of liver enzymes.

Conclusions

Study findings suggest that the administration of 5-ALA as a surgical adjunct for resection and biopsy of primary brain tumors and brain metastases is safe. In light of the high rate of positive fluorescence in high-grade gliomas other than glioblastomas, meningiomas, and a variety of metastatic cancers, 5-ALA seems to be a promising tool for enhancing intraoperative identification of neoplastic tissue and optimizing the extent of resection.

Predictive value of intraoperative 5-aminolevulinic acid-induced fluorescence for detecting bone invasion in meningioma surgery

OBJECT

Bone invasion is a major concern in meningioma surgery, since it is predictive of the recurrence of cranial involvement, morbidity, and mortality. Bone invasion has been reported in 20%-68% of studies with histopathologically confirmed data. Unfortunately, radical resection of bone invasion remains challenging. The aim of this study was to assess the role of 5-aminolevulinic acid (5-ALA) fluorescence in guiding the resection of bone-invading meningiomas. To this purpose, the sensitivity, specificity, and positive and negative predictive values of 5-ALA in detecting meningioma bone invasion were evaluated.

METHODS

Data from 12 patients affected by bone-invading meningiomas (7 with skull base and 5 with convexity meningiomas) who had undergone surgery with the assistance of 5-ALA fluorescence and neuronavigation between July 2012 and March 2013 at the Department of Neurosurgery of Padua were retrospectively analyzed. To evaluate the sensitivity and specificity of 5-ALA fluorescence in detecting meningioma tissue, a pathologist analyzed 98 surgical bone samples under blue light, according to different fluorescence patterns. Magnetic resonance images and CT scans were obtained pre- and postoperatively to determine the extent of bone invasion resection.

RESULTS

The rate of 5-ALA-induced fluorescence of both tumor and bone invasion was 100%. Based on the pathological examination of bone specimens, 5-ALA presented a sensitivity of 89.06% (95% CI 81.41%-96.71%) and a specificity of 100% in detecting meningioma bone invasion, while the positive and negative predictive values were 100% and 82.93% (95% CI 71.41%-94.45%), respectively. At the postoperative stage, MRI did not detect cases of meningioma bone invasion, whereas CT scans revealed residual hyperostosis in 2 cases.

CONCLUSIONS

In summary, 5-ALA fluorescence represents a suitable and reliable technique for identifying and removing bone infiltration by meningiomas. However, further studies are needed to prove the clinical consequences of this promising technique in a larger population.

5-Aminolevulinic acid induced fluorescence is a powerful intraoperative marker for precise histopathological grading of gliomas with non-significant contrast-enhancement

BACKGROUND

Intraoperative identification of anaplastic foci in diffusely infiltrating gliomas (DIG) with non-significant contrast-enhancement on MRI is indispensible to avoid histopathological undergrading and subsequent treatment failure. Recently, we found that 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (PpIX) fluorescence can visualize areas with increased proliferative and metabolic activity in such gliomas intraoperatively. As treatment of DIG is predominantely based on histopathological World Health Organisation (WHO) parameters, we analyzed whether PpIX fluorescence can detect anaplastic foci according to these criteria.

METHODS

We prospectively included DIG patients with non-significant contrast-enhancement that received 5-ALA prior to resection. Intraoperatively, multiple samples from PpIX positive and negative intratumoral areas were collected using a modified neurosurgical microscope. In all samples, histopathological WHO criteria and proliferation rate were assessed and correlated to the PpIX fluorescence status.

RESULTS

A total of 215 tumor specimens were collected in 59 patients. Of 26 WHO grade III gliomas, 23 cases (85%) showed focal PpIX fluorescence, whereas 29 (91%) of 33 WHO grade II gliomas were PpIX negative. In intratumoral areas with focal PpIX fluorescence, mitotic rate, cell density, nuclear pleomorphism, and proliferation rate were significantly higher than in non-fluorescing areas. The positive predictive value of focal PpIX fluorescence for WHO grade III histology was 85%.

CONCLUSIONS

Our study indicates that 5-ALA induced PpIX fluorescence is a powerful marker for intraoperative identification of anaplastic foci according to the histopathological WHO criteria in DIG with non-significant contrast-enhancement. Therefore, application of 5-ALA optimizes tissue sampling for precise histopathological diagnosis independent of brain-shift.

Meningioma

Meningiomas represent the most common primary brain tumor and comprise 3 World Health Organization (WHO) grades, the most frequent being WHO grade I (90%). Surgery is mandatory to establish the diagnosis and to remove the tumor; however, complete resection can be achieved in only <50% of patients. Depending on the extent of resection, tumor location and the WHO grade radiation therapy can be applied. The issue of systemic treatment such as chemotherapy or targeted therapy (eg, somatostatin receptors, antiangiogenic agents) is yet not solved, particularly as current data are derived from small uncontrolled series in patients with long-standing disease and after several pretreatments. A more thorough understanding of molecular genetics, signaling pathways and prognostic factors in meningiomas should lead to the design of studies which stratify according to these factors. These studies have to be conducted in newly diagnosed patients after incomplete resection and in tumors of WHO grade II and III.

Intraoperative fluorescent imaging of intracranial tumors: a review

A review of fluorescent imaging for intracranial neoplasms is presented. Complete resection of brain cancer is seldom possible because of the goal to preserve brain tissue and the inability to visualize individual infiltrative tumor cells. Verification of histology and identification of tumor invasion in macroscopically normal-appearing brain tissue determine prognosis after resection of malignant gliomas. Therefore, imaging modalities aim to facilitate intraoperative decision-making. Intraoperative fluorescent imaging techniques have the potential to enable precise histopathologic diagnosis and to detect tumor remnants in the operative field. Macroscopic fluorescence imaging is effective for gross tumor detection. Microscopic imaging techniques enhance the sensitivity of the macroscopic observations and provide real-time histological information. Further development of clinical grade fluorescent agents specifically targeting tumor cells could improve the diagnostic and prognostic yield of intraoperative imaging.