Quantitative fluorescence in intracranial tumor: implications for ALA-induced PpIX as an intraoperative biomarker

Abstract

Object Accurate discrimination between tumor and normal tissue is crucial for optimal tumor resection. Qualitative fluorescence of protoporphyrin IX (PpIX), synthesized endogenously following δ-aminolevulinic acid (ALA) administration, has been used for this purpose in high-grade glioma (HGG). The authors show that diagnostically significant but visually imperceptible concentrations of PpIX can be quantitatively measured in vivo and used to discriminate normal from neoplastic brain tissue across a range of tumor histologies. Methods The authors studied 14 patients with diagnoses of low-grade glioma (LGG), HGG, meningioma, and metastasis under an institutional review board–approved protocol for fluorescence-guided resection. The primary aim of the study was to compare the diagnostic capabilities of a highly sensitive, spectrally resolved quantitative fluorescence approach to conventional fluorescence imaging for detection of neoplastic tissue in vivo. Results A significant difference in the quantitative measurements of PpIX concentration occurred in all tumor groups compared with normal brain tissue. Receiver operating characteristic (ROC) curve analysis of PpIX concentration as a diagnostic variable for detection of neoplastic tissue yielded a classification efficiency of 87% (AUC = 0.95, specificity = 92%, sensitivity = 84%) compared with 66% (AUC = 0.73, specificity = 100%, sensitivity = 47%) for conventional fluorescence imaging (p < 0.0001). More than 81% (57 of 70) of the quantitative fluorescence measurements that were below the threshold of the surgeon's visual perception were classified correctly in an analysis of all tumors. Conclusions These findings are clinically profound because they demonstrate that ALA-induced PpIX is a targeting biomarker for a variety of intracranial tumors beyond HGGs. This study is the first to measure quantitative ALA-induced PpIX concentrations in vivo, and the results have broad implications for guidance during resection of intracranial tumors.

Low dose 5-aminolevulinic acid: Implications in spectroscopic measurements during brain tumor surgery

“…As the detection sensitivity of the probe is higher than the microscope [11,13] application of ALA at a lower dose [14] may be possible when spectroscopic detection techniques are used during open biopsy, stereotactic biopsy or even open brain surgery. In a previous study initial results for tissue discrimination using low ALA dose has been published [15].…”

405 nm versus 633 nm for protoporphyrin IX excitation in fluorescence‐guided stereotactic biopsy of brain tumors

“…Beyond stereotactic biopsies, these results on the practical implications of blood interference are also very relevant for fluorescence guidance in open brain surgery, e.g. when examining the resection cavity with a fiber optical probe as described in [27,28].…”

“…[22][23][24] A tumor-related deficient blood brain barrier and an altered activity level of several enzymes including ferrochelatase, which catalyzes the conversion of PpIX to heme, are central reasons for this phenomenon. [25] Tumor recognition with 5-ALA-induced PpIX is already effectively used for fluorescence-guided resection of malignant gliomas using surgical microscopes [22,23,26] or fiber optical probes [27,28]. It leads to a significantly increased complete resection rate of these diffusely growing tumors and to a significantly enhanced progression-free survival rate after 6 months, translating into a progression-free survival prolongation of 1.5 months as compared to conventional white light resection.…”

Epithelial Growth Factor Receptor Expression influences 5-ALA Induced Glioblastoma Fluorescence

“…Clinically, the exogenous, oral administration of 5-ALA is usually performed 4h prior to surgery. 5-ALA is resorbed through the upper intestine into the blood, where it diffuses through the blood-brain barrier, which has been typically disrupted by infiltrative tumor cells [5][6][7][8][9]. During fluorescence assisted tumor resection a variance of the fluorescence intensity within GBM can be observed, especially at the infiltrating zone [4,8,10].…”

“…5-ALA is resorbed through the upper intestine into the blood, where it diffuses through the blood-brain barrier, which has been typically disrupted by infiltrative tumor cells [5][6][7][8][9]. During fluorescence assisted tumor resection a variance of the fluorescence intensity within GBM can be observed, especially at the infiltrating zone [4,8,10]. 5-ALA induced fluorescence may vary upon many factors such as cell density, proliferation index, mitochondrial mass and index and furthermore exogenous factors such as application or fading during surgery [5][6][7][8].…”