Brain malignancies are still associated with poor prognosis despite multimodal radiosurgical therapeutic
approach using Gamma Knife (GK), CyberKnife (CK), and linear accelerator-based technologies [1]. These
advances have significantly improved the treatment outcome. However, the surgical and radiosurgical
concept is still “image-guided”, and the success is closely related to precise tumor volume definition. The
gross tumor volume (GTV) is defined as the visible contrast- enhancing lesion on magnetic resonance (MR)
images with high three-dimensional spatial accuracy. Target delineation requires always both T2-weighted
and volumetric T1-weighted sequences. T2-weighted fluid attenuated inversion recovery (FLAIR) sequences
analyze the lesions surrounding brain tissues [2,3].
Objective assessment of apparently healthy tissue surrounding brain tumors seems to be a considerable
factor interfering not only with the radiosurgical procedure, but also with the recurrence rate and overall
survival. Several studies identified infiltrative spectroscopic pattern of the perilesional edema in more than
96% of high-grade gliomas cases and in 11,5% of patients with brain metastasis [4]. Moreover, some
autopsy series of brain metastases confirmed infiltrative growth in radiologically healthy surrounding tissues
in more than 60% of cases. This unseen malignant component is responsible of 80 % of “early recurrence”
which should be considered as natural evolution of the main tumor [5]. In the management of high grade
gliomas, the radiosurgeons are faced either to carcinologic incomplete procedures or to overestimated target
irradiation with unbalanced benefit/risk action mostly related to radiation-induced brain necrosis [6]. The
delineation of clinical target volume (CTV) which is defined as the volume of tissue that contains the GTV
and any microscopic tumor or paths of spread, became a standard for any radio-surgical planning. Since a
decade, the magnetic resonance spectroscopy (MRS) was standardized in the target volume assessment.
The aim is to establish a metabolic lesional cartography. It had been reported that choline/ N- acetylaspartate
(NAA) multivoxel MR spectroscopy index higher that 2,5 is in favor of malignancy in glioma with sensitivity
of 90 % and specificity of 85 % [7]. However, NAA/Creatine (Cr) and Choline/Cr ratios are more relevant in
the analysis of perilesional edema in brain metastasis cases. The introduction of MRS metabolic cartography
concept, the use of relevant metabolite and adapted metabolites ratio estimation contributed to precision in
radiosurgery. However, MRS is not used for target delineation for Gamma Knife radiosurgical treatment
because of its incompatibility with the Leksell Gamma Knife planning software. Recently, we described the
development of the first software allowing the integration of metabolic cartography based on multivoxel
spectroscopic MRI in the radiosurgical planning for Leksell Gamma Knife Radiosurgery.
The few existing meta-analysis could not lead to gold standard volume delineation techniques despite
objective advance in imaging assessment [8,9]. Prospective studies using multimodal imaging data will help
to overcome this insufficiency for target delineation in radiosurgery
USE OF PROTON MAGNETIC RESONANCE SPECTROSCOPIC IMAGING DATA IN PLANNING FOCAL RADIATION THERAPIES FOR BRAIN TUMORS
