5-ALA Photodynamic Therapy in Neurosurgery, Towards the Design of a Treatment Planning System: A Proof of Concept

•Photodynamic therapies are promising solutions for treatment of glioblastoma.•A proof of concept for planning stereotactic interstitial photodynamic therapy is described.•Algorithms of light transport modeling are compared.•Optical fiber needed to transport light into the tumor core can be planned with an error below 1 mm.

Purpose. Glioblastoma (GBM) treatment still remains a complex challenge. Among alternatives or adjuvant therapies, photodynamic therapy (5-ALA PDT) appears to be a promising approach. 5-ALA PDT can be delivered intraoperatively, early after tumor resection, or interstitially according to brain tumor location. A treatment planning system was designed to manage dosimetry issues before PDT delivery.Methods. The TPS was developed according to a specific workflow from stereotactic image registration to light fluence rate modeling. Here, we describe a proof of concept of a treatment planning system (TPS) dedicated to interstitial 5-ALA PDT. This tool enables the planning of a whole treatment in surgical stereotactic conditions. Stereotactic registration and dosimetry components are detailed and evaluated. The registration process is compared to a commercial solution (Leksell Gamma Plan®, Elekta®, Sweden) defined as the ground truth and dosimetry model implemented in our TPS and is compared to numerical simulations.Results. Registration achieved a sub-millimetric mean relative error that matched the standard MRI resolution. Dosimetry comparison showed a negligible error between analytical and numerical models and enabled a validation of the dosimetry algorithm implemented.Conclusions. A treatment planning system was designed to achieve 5-ALA PDT simulations before the patients underwent surgery. Similarly, for radiation therapy, we proposed a system to plan and evaluate the 5-ALA PDT dosimetry for optimizing treatment delivery. Although this system remains to be perfected, this preliminary work aimed to demonstrate the feasibility of planning 5-ALA PDT treatments in stereotactic conditions. Future improvements will mainly focus on the optimization of the treatment delivery, automatic segmentation and GPU-accelerated Monte-Carlo management to take into account GBM tissue heterogeneity.

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