PET/MRI and brain tumors: focus on radiation oncology treatment planning

Abstract

In brain tumors, imaging by magnetic resonance imaging (MRI) can very accurately visualize anatomy and morphology of healthy and malignant tissue, but neither contrast-enhancing areas in T1-weighted sequences, nor hyperintensities in T2/FLAIR sequences are specific for tumor tissue, especially when considering the manifold alterations resulting from previous treatment. Imaging the biology of tumor tissue by positron emission tomography (PET), therefore, is a highly interesting approach to improve the detection of macroscopic tumor which is the prerequisite for high-precision radiotherapy treatment planning. This review will focus on the benefits of amino acid tracers (L-[methyl-11 C]methionine (MET) and O-(2-[ 18 F]fluoroethyl)-L-tyrosine (FET)) in neurooncology and their implementation in radiation oncology. Furthermore, a brief overview of the current impact of 2-deoxy-2-(18F)fluoro-D-glucose (FDG), nucleic acid analogs, hypoxia tracers, and Somatostatin receptor (SSTR) analogs on radiotherapy planning in brain tumors is provided. Among advances in multiparametric MRI, Diffusionweighted imaging (DWI) has attracted particular attention since it can predict prognosis, as well as indicate response to treatment and has already been introduced into target volume definition for radiotherapy of various cancers (e.g., prostate and rectal cancer). Additionally, advances in MR spectroscopy (MRS) are mentioned. Finally, these findings will be discussed concerning their influence on current aspects of integrated PET/MR hybrid imaging.

Rigid-body motion correction in hybrid PET/MRI using spherical navigator echoes

“…Integrated positron emission tomography and magnetic resonance imaging (PET/MRI) is a promising hybrid imaging modality that can provide simultaneous functional and anatomic information. For neuroimaging, PET/ MRI is especially promising for imaging in oncology (Oehlke and Grosu 2017), focal epilepsy (Paldino et al 2017) and neurodegenerative disorders (Barthel et al 2015). However, both PET and MRI are highly susceptible to patient motion due to long acquisition times.…”

Technical Note: Adapting a GE SIGNA PET/MR scanner for radiotherapy

“…The use of advanced pretreatment imaging is increasing in radiotherapy (RT). Magnetic resonance imaging (MRI) and positron emission tomography (PET) are today widely used for target definition for several common indications for radiotherapy, for example, prostate cancer, lung cancer, intracranial malignances, and head and neck cancer . Potential novel applications include quantitative PET and MR imaging to facilitate dose painting by numbers, objective or automatic identification of target volumes, or stratification of patients to different treatment regimens …”

Neuroimaging Studies Evaluating Effective Therapies for High-Grade Glioma

“…34 This could be extremely useful to better guide biopsies of regions of the tumour with different characteristics, but also to better inform surgical and radiotherapy planning to address the large burden of infiltrating tumour cells that are often responsible for tumour recurrence. 12,35 Another important application of PET imaging in neuro-oncology is in planning and assessing clinical trials evaluating the potential of therapeutic agents. 36 The ability to visually monitor targeting agents pharmacokinetics, biodistribution and tumour specific uptake in vivo allows for the early screening of novel therapeutic drugs, for patients stratification and for evaluating potential for radionuclide targeted therapy.…”