MRI assessment of treatment delivery for interstitial photodynamic therapy of high‐grade glioma in a preclinical model

Background High‐grade gliomas are primary brain tumors that have shown increasing incidence and unfavorable outcomes. Local control is crucial to the management of this pathology. Photodynamic therapy (PDT), based on the light‐induced activation of a photosensitizer (PS), achieves local treatment by inducing selective lesions in tumor tissue. Objectives Previous studies have reported the outcomes of PDT for glioblastoma via immunohistological data. Our study aimed to evaluate MRI findings, including diffusion, and perfusion sequences, compared with immunohistological data from the same population to address the efficiency of light fractionation. Materials and Methods Twenty‐six “nude” rats grafted with human U87 cells into the right putamen underwent PDT. After PS precursor (5‐ALA) intake, an optical fiber was introduced into the tumor. The rats were randomized into the following groups: those without illumination and those that received two or five fractions of light. Treatment effects were assessed with early high‐field MRI to measure the volume of necrosis and edema using diffusion and perfusion sequences; the MRI results were compared with immunohistology results, including necrosis and apoptosis markers. Results Elevated diffusion values were observed on MRI in the centers of the tumors of the treated animals, especially in the 5‐fraction group (P