Possibilities of interstitial photodynamic therapy in the treatment of brain glioblastoma

Interstitial photodynamic therapy (iPDT) is a minimally invasive treatment method based on the interaction of light, a photosensitizer (PS) and oxygen. In brain gliomas, iPDT involves the stereotactic introduction of one or more light guides into the target area to irradiate tumor cells and tissues that have accumulated PS, which subsequently causes necrosis and/or apoptosis of tumor cells, destruction of the tumor vascular network and causes an inflammatory reaction that triggers stimulation of the antitumor immune response. The aim of the study was to analyze the possibility of using iPDT in the treatment of unifocal, small-sized (up to 3.5 cm) glioblastomas. The study with iPDT included 7 patients with a unifocal variant of glioblastoma with a maximum tumor size of up to 3.5 cm and a Karnofsky score of at least 70 points. In 5 patients (71.4%) there was a relapse of glioblastoma, in 2 cases (28.6%) the tumor was diagnosed for the first time. As a PS, PS photoditazine was used, administered intravenously by drip at a dose of 1 mg/kg. Interstitial irradiation was performed using a laser (Latus 2.5 (Atkus, Russia)) with a wavelength of 662 nm and a maximum power of 2.5 W and cylindrical scattering fibers. The target tumor volume was determined after combining multimodal CT images (contrast-enhanced scanning, axial slices of 0.6 mm) with preoperative MRI, PET. Spatial precise interstitial irradiation of the tumor volume was planned using special software. The duration of irradiation did not exceed 15 min. The light dose was from 150 to 200 J/cm2. Transient clinical deterioration was recorded in about 2 patients (28.6%). These 2 patients had worsening neurological deficits in the early postoperative period (increase in hemiparesis from 4 points to 2 points in one patient and development of dysarthria and dysphasia in the second patient). The median overall survival from the first diagnosis of malignant glioma to death was 28.3 months. The median relapse-free survival was 13.1 months. MGMT status played a significant role in the outcome of patients treated with iPDT. Patients with a methylated MGMT promoter survived longer than patients with an unmethylated MGMT promoter by a median of 22.1 months, and they did not experience disease progression for an additional 9.3 months. iPDT may be a promising treatment option in a population of patients at high risk of postoperative neurological deficit. It does not interfere with, but rather may complement, other treatment options for this disease, such as repeat radiation therapy and chemotherapy. iPDT remains a potential option for deep-seated gliomas in patients with high surgical risk and in case of tumor recurrence.