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Citation: Hassini Derkaoui F. Contribution of spectroscopic magnetic resonance imaging to target volume delineation in Gamma

https://doi.org/10.32512/jmr.4.1.2021/2

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Editorial

Contribution of spectroscopic magnetic resonance imaging to target volume

delineation in Gamma Knife Radiosurgery: Myth or reality?

Dr. Fahd Derkaoui Hassani

Department of Neurosurgery, Cheikh Zaid International University Hospital, Rabat, Morocco.

Abulcasis International University of Health Sciences, Rabat, Morocco.

Mohammed V University of Rabat, Rabat, Morocco.

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.

References

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[2] Ajithkumar T, Horan G, Padovani L, Thorp N, Timmermann B, Alapetite C, et al. SIOPE - Brain tumor group consensus guideline on craniospinal target volume delineation for high-precision radiotherapy. Radiother Oncol. 2018; 128:192-97.

[3] Tong E, McCullagh KL, Iv M. Advanced Imaging of Brain Metastases: From Augmenting Visualization and Improving Diagnosis to Evaluating Treatment Response. Front Neurol. 2020;11:270.

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[5] Lee CC, Lee WK, Wu CC, Lu CF, Yang HC, Chen YW, et al. Applying artificial intelligence to longitudinal imaging analysis of vestibular schwannoma following radiosurgery. Sci Rep. 2021;11:3106.

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[7] McKnight TR, Von dem Bussche MH, Vigneron DB, Lu Y, Berger MS, McDermott MW, et al. Histopathological validation of a three-dimensional magnetic resonance spectroscopy index as a predictor of tumor presence. J Neurosurg. 2002; 97:794-802.

[8] Loi M, Caini S, Scoccianti S, Bonomo P, De Vries K, Francolini G, et al. Stereotactic reirradiation for local failure of brain metastases following previous radiosurgery: Systematic review and meta-analysis. Crit Rev Oncol Hematol. 2020; 153:103043.

[9] Akanda ZZ, Hong W, Nahavandi S, Haghighi N, Phillips C, Kok DL. Post-operative stereotactic radiosurgery following excision of brain metastases: A systematic review and meta-analysis. Radiother Oncol. 2020; 142:27-35.