The role of medical imaging in the context of photodynamic therapy

International audiencePhotodynamic therapy (PDT) is a modality with promising results for the treatment of various cancers. PDT is increasingly included in the standard of care for different pathologies. The role of medical imaging in this context is crucial to better understand how and where to deliver the therapy but also to observe the different mechanisms involved in the effects on tumors. At different stages of delivery, PDT requires imaging to plan, evaluate and monitor treatment. In this paper, we review the contribution of Magnetic Resonance Imaging or Positron Emission Tomography for planning and therapeutic monitoring purposes. Several solutions have been proposed to plan PDT from imaging. MRI and dedicated segmentation algorithm have been recently proposed to plan interstitial PDT with stereotactic localization and light diffusion simulation capabilities. Additionally, photosensitizer biodistribution has been evaluated with radiolabeled photosensitizers. The effects of PDT delivery have also been explored with specific Magnetic Resonance Imaging or Positron Emission Tomography radiopharmaceuticals to evaluate the effects on cells (apoptosis, necrosis, proliferation, metabolism) or vascular damage. The contribution of medical imaging in the context of photodynamic therapies is important and continues to increase. Using morphological or molecular imaging has to be considered for future developments of PDT

On image segmentation methods applied to glioblastoma: state of art and new trends

International audienceBecause of high heterogeneity and invasiveness, treatment of GlioBlastoma Multiform (GBM) still remains a complex challenge. Several recent advanced therapies have improved precision of treatment deliverance. Multimodality imaging plays an increasingly important role in this process and images segmentation has become an essential part of the pipeline of standard treatment planning system. With the sophistication of multimodality information, the development of reliable and robust segmentation algorithms to overcome manual segmentation and optimize targeted treatment is highly expected. In this paper, we first introduce targeted therapies applied in the GBM clinical care, from routine or research. Different segmentation methods from state of the art are highlighted to achieve GBM delineation. New trends in GBM segmentation such as machine learning and multimodal features are discussed. These additional frameworks may achieve segmentation with refining capacities, active tumour probability mapping and, even, tumour relapse prediction capacities

Multimodal imaging in radiotherapy: Focus on adaptive therapy and quality control

International audienceImproved computer resources in radiation oncology department have greatly facilitated the integration of multimodal imaging into the workflow of radiation therapy. Nowadays, physicians have highly informative imaging modalities of the anatomical region to be treated. These images contribute to the targeting accuracy with the current treatment device, impacting both segmentation or patient's positioning. Additionally, in a constant effort to deliver personalized care, many teams seek to confirm the benefits of adaptive radiotherapy. The published works highlight the importance of registration algorithms, particularly those of elastic or deformable registration necessary to take into account the anatomical evolutions of the patients during the course of their therapy. These algorithms, often considered as "black boxes", tend to be better controlled and understood by physicists and physicians thanks to the generalization of evaluation and validation methods. Given the still significant development of medical imaging techniques, it is foreseeable that multimodal registration needs require more efficient algorithms well integrated within the flow of data

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

International audiencePurpose: 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 tumour resection, or interstitially according to brain tumour 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 modelling. 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

Biologically effective dose and prediction of obliteration of unruptured arteriovenous malformations treated by upfront Gamma Knife radiosurgery: a series of 149 consecutive cases.

Arteriovenous malformations (AVMs) present no pathologic tissue, and radiation dose is confined in a clear targeted volume. The authors retrospectively evaluated the role of the biologically effective dose (BED) after Gamma Knife radiosurgery (GKRS) for brain AVMs. A total of 149 consecutive cases of unruptured AVMs treated by upfront GKRS in Lille University Hospital, France, were included. The mean length of follow-up was 52.9 months (median 48, range 12-154 months). The primary outcome was obliteration, and the secondary outcome was complication appearance. The marginal dose was 24 Gy in a vast majority of cases (n = 115, 77.2%; range 18-25 Gy). The mean BED was 220.1 Gy2.47 (median 229.9, range 106.7-246.8 Gy2.47). The mean beam-on time was 32.3 minutes (median 30.8, range 9-138.7 minutes). In the present series, the mean radiation dose rate was 2.259 Gy/min (median 2.176, range 1.313-3.665 Gy/min). The Virginia score was 0 in 29 (19.5%), 1 in 61 (40.9%), 2 in 41 (27.5%), 3 in 18 (12.1%), and 4 in 0 (0%) patients, respectively. The mean Pollock-Flickinger score was 1.11 (median 1.52, range 0.4-2.9). Univariate (for obliteration and complication appearance) and multivariate (for obliteration only) analyses were performed. A total of 104 AVMs (69.8%) were obliterated at the last follow-up. The strongest predictor for obliteration was BED (p = 0.03). A radiosurgical obliteration score is proposed, derived from a fitted multivariable model: (0.018 × BED) + (1.58 × V12) + (-0.013689 × beam-on time) + (0.021 × age) - 4.38. The area under the receiver operating characteristic curve was 0.7438; after internal validation using bootstrap methods, it was 0.7088. No statistically significant relationship between radiation dose rate and obliteration was found (p = 0.29). Twenty-eight (18.8%) patients developed complications after GKRS; 20 (13.4%) of these patients had transient adverse radiological effects (perilesional edema developed). Predictors for complication appearance were higher prescription isodose volume (p = 0.005) and 12-Gy isodose line volume (V12; p = 0.001), higher Pollock-Flickinger (p = 0.02) and Virginia scores (p = 0.003), and lower beam-on time (p = 0.03). The BED was the strongest predictor of obliteration of unruptured AVMs after upfront GKRS. A radiosurgical score comprising the BED is proposed. The V12 appears as a predictor for both efficacy and toxicity. Beam-on time was illustrated as statistically significant for both obliteration and complication appearance. The radiation dose rate did not influence obliteration in the current analysis. The exact BED threshold remains to be established by further studies