Spectroscopic fluorescence measurements as an intraoperative tool for glioma resection

International audienceContext: Gliomas account for 80% of malignant primitive tumors of the central nervous system. It is the most common primary brain tumor in adults, with a median age at diagnosis of 64 years. They are infiltrative cancers and are often not curable. Surgery is the first step to treat gliomas and studies have shown that the survival rate is linked with the quality of the surgery. Thus, it is mandatory to get the most extended resection. Today, 5-ALA-induced protoporphyrin IX (PpIX) fluorescence is widely used to help the surgeon distinguish infiltrative compound of gliomas. The current methods are based on intraoperative surgical fluorescence microscopy or optical fiber systems that allow a local emission spectrum measurement or a quantification of 5-ALA-induced PpIX concentration. However, the accuracy of such technics remains limited because of a still low sensitivity to evaluate infiltrative compound of gliomas.We demonstrated in a previous in vitro and ex vivo study that the PpIX spectrum is more complex than expected. Biopsies were from patients with glioblastomas (GBM), which are high grade gliomas. We showed that, added to the known peak at 634 nm (PpIX634), a second peak appears sometimes at 620 nm (PpIX620). We assumed that those two peaks correspond to two states of PpIX, which depend on the microenvironment. Knowing this, we proposed new measured parameters to distinguish the solid component of GBM from low grade gliomas and infiltrative component of GBM [10]. Figure 1 shows the ratio between the two states and discrimination of the solid component of GBM.Our goal is then to create an intraoperative tool based on fluorescence spectroscopy to assist the surgeon during tumor’s margins resection. This paper focuses on new instrumental development to distinguish the two states of PpIX, based on multi-wavelength excitation