Radiological and Thermal Dose Correlations in Pallidothalamic Tractotomy With MRgFUS.

Background: MR-guided focused ultrasound (MRgFUS) offers the possibility of safe and accurate lesioning inside the brain. Until now, most MRgFUS thermal applications have been based on temperature or energy protocols. Experimental studies support however an approach centered on thermal dose control. Objective: To show the technical feasibility and lesion size predictability of a thermal dose approach during MRgFUS pallidothalamic tractotomy (PTT) against chronic therapy-resistant Parkinson's disease (PD). Methods: MR and thermal dose data were analyzed in 31 MRgFUS interventions between January and December 2017 in patients suffering from chronic therapy-resistant Parkinson's disease (PD) using a standardized PTT target covered by 5 to 7 target lesion sub-units. Results: Good correlations were found between (1) the mean axial T2 lesion diameter intraoperatively and the mean 240 cumulative equivalent min at 43°C (240 CEM) thermal dose diameter (r = 0.52), (2) the mean axial T2 diameter 48 h post-treatment and the mean 18 CEM thermal dose diameter (r = 0.62), and (3) the mean axial T2 diameter intraoperatively and 48 h post-treatment (r = 0.62). Conclusion: Our current approach using a thermal dose steering for multiple target lesion sub-units could be reproduced in 31 interventions with a good lesion size predictability.

Introduction

Purpose Thermal ablation

Study Objective To demonstrate the technical feasibility and lesion size predictability of a thermal-dose-controlled MR-guided focused ultrasound approach for pallidothalamic tractotomy in patients with chronic therapy-resistant Parkinson's disease.

Animal model / Human subject Human (Homo sapiens), strain: N/A, mean age 67 ± 11 years, sex: not reported

Disease model Parkinson's disease (chronic therapy-resistant)

MRI or image guidance method MR-guided (MRgFUS) using the ExAblate Neuro system integrated with a 3-Tesla MRI (GE Discovery 750); atlas-based spatial coverage targeting with 5–7 preplanned focal positions and intraoperative MR T2 monitoring and thermal-dose mapping (ExAblate software).

Targeted brain region(s) Pallidothalamic Tract (Pallidothalamic Tractotomy, Ptt)

Cargo name and characteristics Focused ultrasound thermal energy (thermal ablation): MR-guided focused ultrasound (ExAblate Neuro) delivering focal thermal doses aiming for 240 CEM (cumulative equivalent minutes at 43°C) per sonication (focal region ~1.5×1.5×3.0 mm); 18 CEM noted as ~50% damage threshold. Adjunct/perioperative medications: corticosteroids — IV methylprednisolone (Solumedrol) ~40 mg after last sonication (and at 12 h) and oral dexamethasone 3×2 mg/day for 3–4 days.

Route of administration Intravenous (Solumedrol corticosteroid), oral (dexamethasone)

Outcomes and Safety

Summary of Outcomes MRgFUS pallidothalamic tractotomy produced predictable lesion sizes that correlated with thermal dose metrics (intraoperative T2 diameter correlated with 240 CEM, r=0.52; 48 h T2 diameter correlated with 18 CEM, r=0.62), and the thermal‑dose‑steered multi‑subtarget approach was reproducibly achieved in 31 cases. Successful parameters identified were the 240 CEM (LD100) and 18 CEM (50% damage) thermal dose thresholds and a strategy of multiple short‑duration sonications distributed across 5–7 subtargets.

Duration of biological effect 1 year

Safety-related matter The paper reports development of intralesional cytotoxic and perilesional vasogenic edema during the first 2 postoperative days (described as non-lesional) and emphasizes that thermal dose steering is important to preserve safety of surrounding structures; no specific adverse events or complications are reported in the text.

Brain Region

Ultrasound Parameters

Ultrasound instrument ExAblate Neuro (InSightec, Haifa, Israel); transducer aperture/diameter: None

Focal Characteristics focal depth: 3.0 mm; focal length: None; aperture size: None

Treatment frequency Single session

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