Letter: The Impact of Extent of Ablation on Survival of Patients With Newly Diagnosed Glioblastoma Treated With Laser Interstitial Thermal Therapy: A Large Single-Institutional Cohort

Abstract

To the Editor:We read with great enthusiasm the article regarding the impact of the extent of ablation using laser interstitial thermal therapy (LITT) in survival of patients with newly diagnosed glioblastoma published by Kaisman-Elbaz et al. 1 LITT provides a valuable alternative of treatment for patients with few surgical options, such as diagnosis of highly eloquent and/or deep-seated glioblastomas (GBM), and for patients who have a high frailty index. [2][3][4] To date, the literature has highlighted inconsistencies in the technique, indications, patient selection, and functional outcomes and impact in overall survival (OS) and progressionfree survival (PFS). 5,6 The focus in LITT has been recurrent GBM and not necessarily newly diagnosed GBM. 7 Recurrent GBM is a different disease entity which is more challenging to treat since patients have usually undergone multiple lines of therapy.Kaisman-Elbaz et al 1 show that near total ablation was statistically significant in promoting OS (P = .008) in newly diagnosed GBM. In real terms, PFS was considerably higher-10.4 months-as well as OS-22.7 months-in 10 patients who had near total ablation; this is equivalent to surgical resectionrelated OS of 15 months 1 or 17.5 months in 5-Aminolevulinic acid-assisted gross total resections. 8 Kaisman-Elbaz et al 1 also report 84% of patients with excess ablation (ExA) (between 0.25 and 35.3 cc) performed with no neurological deficit. At least 75% of this cohort had lesions which were in deep or eloquent regions. 1 Neurological function is more likely to be located beyond the margins of the lesion in GBM than within the lesion. Hence, if a significant proportion of patients had ablation outside the lesion, they are more susceptible in developing neurological deficit. It would be interesting to know whether authors would consider intraoperative neuromonitoring and preoperative mapping, particularly using tractography or connectomics, to improve or prevent neurological deficits.The literature suggests some thresholds of lesion-to-tract distance more likely to cause neurological deficit 9,10 during tumor resections that have been incorporated in risk stratification scores. The corticospinal tract has high thermal susceptibility, 11 and its damage can lead to significant disability. It is crucial to assess the impact of lesion-to-tract distance to establish the risk of neurological deficit with regard to different tracts of interest to maximize the safety of LITT ablation. It is also significant to note that the

In Reply: The Impact of Extent of Ablation on Survival of Patients With Newly Diagnosed Glioblastoma Treated With Laser Interstitial Thermal Therapy: A Large Single-Institutional Cohort

“…We agree with Awan et al 1 regarding the potential of excess ablation contribution to glioblastoma patients' overall survival and progression-free survival, possibly similar to supramaximal resection accumulating data. In our study, no benefit regarding those oncological parameters was demonstrated.…”

“…In their letter, Awan et al 1 referred to the high excess ablation rate detected in 84% of our patient cohort 2 that was not found to cause a new postprocedural neurological deficit. They describe thoroughly the importance of protecting critical brain structures such as the corticospinal tract during laser interstitial thermal therapy and evaluating the distance of those structures from the treated lesion before the procedure.…”

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To the Editor:We appreciate the letter to the editor submitted to the Neurosurgery journal recently by Awan et al 1 This letter addresses several important aspects of our work 2 that are to be clarified accordingly.In their letter, Awan et al 1 referred to the high excess ablation rate detected in 84% of our patient cohort 2 that was not found to cause a new postprocedural neurological deficit. They describe thoroughly the importance of protecting critical brain structures such as the corticospinal tract during laser interstitial thermal therapy and evaluating the distance of those structures from the treated lesion before the procedure.Our protocol consists of conducting preprocedural fiber tracking and importing them to the NeuroBlate system to ensure no overlap between the ablation zone and eloquent brain structures.

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“…We appreciate the letter to the editor submitted to the Neurosurgery journal recently by Awan et al 1 This letter addresses several important aspects of our work 2 that are to be clarified accordingly.…”