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Purvee Patel, Nitesh V. Patel and Shabbar F. Danish

OBJECTIVE

MR-guided laser-induced thermal therapy (MRgLITT) can be used to treat intracranial tumors, epilepsy, and chronic pain syndromes. Here, the authors report their single-center experience with 102 patients, the largest series to date in which the Visualase thermal therapy system was used.

METHODS

A retrospective analysis of all patients who underwent MRgLITT between 2010 and 2014 was performed. Pathologies included glioma, recurrent metastasis, radiation necrosis, chronic pain, and epilepsy. Laser catheters were placed stereotactically, and ablation was performed in the MRI suite. Demographics, operative parameters, length of hospital stay, and complications were recorded. Thirty-day readmission rates were calculated by using the standard method according to America's Health Insurance Plans Center for Policy and Research guidelines.

RESULTS

A total of 133 lasers were placed in 102 patients who required intervention for intracranial tumors (87 patients), chronic pain syndrome (cingulotomy, 5 patients), or epilepsy (10 patients). The procedure was completed in 98% (100) of these patients. Ninety-two patients (90.2%) had undergone previous treatment for their intracranial tumors. The average (± SD) total procedural time was 170.5 ± 34.4 minutes, and the mean laser-on time was 8.7 ± 6.8 minutes. The average intensive care unit (ICU) and hospital stays were 1.8 and 3.6 days, respectively, and the median length of stay for both the ICU and the hospital was 1 day. By postoperative Day 1, 54% of the patients (n = 55) were neurologically stable for discharge. There were 27 cases of morbidity, including new-onset neurological deficits, and 2 perioperative deaths. Fourteen patients (13.7%) developed new deficits after the MRgLITT procedure, and of those 14 patients, 64.3% (n = 9) had complete resolution of deficits within 1 month, 7.1% (n = 1) had partial resolution of symptoms within 1 month, 14.3% (n = 2) had not had resolution of symptoms at the most recent follow-up, and 14.3% (n = 2) died without resolution of symptoms. The 30-day readmission rate was 5.6%

CONCLUSIONS

MRgLITT, although minimally invasive, must be used with caution. Thermal damage to critical and eloquent structures can occur despite MRI guidance. Once the learning curve is overcome, the overall procedural complication rate is low, and most patients can be discharged within 24 hours, with a relatively low readmission rate. In cases in which they occurred, most neurological deficits were temporary. The therapeutic role of MRgLITT in various intracranial diseases will require larger and more rigorous studies.

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Sean M. Munier, Eric L. Hargreaves, Nitesh V. Patel and Shabbar F. Danish

OBJECTIVE

Intraoperative dynamics of magnetic resonance–guided laser-induced thermal therapy (MRgLITT) have been previously characterized for ablations of naive tissue. However, most treatment sessions require the delivery of multiple doses, and little is known about the ablation dynamics when additional doses are applied to heat-damaged tissue. This study investigated the differences in ablation dynamics between naive versus damaged tissue.

METHODS

The authors examined 168 ablations from 60 patients across various surgical indications. All ablations were performed using the Visualase MRI-guided laser ablation system (Medtronic), which employs a 980-nm diffusing tip diode laser. Cases with multiple topographically overlapping doses with constant power were selected for this study. Single-dose intraoperative thermal damage was used to calculate ablation rate based on the thermal damage estimate (TDE) of the maximum area of ablation achieved (TDEmax) and the total duration of ablation (tmax). We compared ablation rates of naive undamaged tissue and damaged tissue exposed to subsequent thermal doses following an initial ablation.

RESULTS

TDEmax was significantly decreased in subsequent ablations compared to the preceding ablation (initial ablation 227.8 ± 17.7 mm2, second ablation 164.1 ± 21.5 mm2, third ablation 124.3 ± 11.2 mm2; p = < 0.001). The ablation rate of subsequent thermal doses delivered to previously damaged tissue was significantly decreased compared to the ablation rate of naive tissue (initial ablation 2.703 mm2/sec; second ablation 1.559 mm2/sec; third ablation 1.237 mm2/sec; fourth ablation 1.076 mm/sec; p = < 0.001). A negative correlation was found between TDEmax and percentage of overlap in a subsequent ablation with previously damaged tissue (r = −0.164; p < 0.02).

CONCLUSIONS

Ablation of previously ablated tissue results in a reduced ablation rate and reduced TDEmax. Additionally, each successive thermal dose in a series of sequential ablations results in a decreased ablation rate relative to that of the preceding ablation. In the absence of a change in power, operators should anticipate a possible reduction in TDE when ablating partially damaged tissue for a similar amount of time compared to the preceding ablation.

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Nitesh V. Patel, Pinakin R. Jethwa, Anil Shetty and Shabbar F. Danish

OBJECT

Although control of intracranial ependymomas is highly correlated with degree of resection, it is unknown if the same is true for MRI-guided laser-induced thermal therapy (MRgLITT). The authors report their experience with MRgLITT for ependymoma and examine the utility of the real-time thermal damage estimate (TDE), a recent software advance, with respect to completeness of ablation and impact on tumor control. To the authors' knowledge, this is the largest single-center experience utilizing MRgLITT for recurrent ependymomas.

METHODS

Five tumors in 4 patients were treated with the Visualase Thermal Therapy System. Two tumors were treated similarly on recurrence. Ablation was performed using a 980-nm diode laser with a real-time image acquisition system. Single-plane TDEs were calculated and compared with the original lesion area to compute percentage area ablated (PAA). Volumetric analysis was performed, and percentage volume ablated (PVA) was estimated and correlated with the TDE. Tumor control was correlated with the TDE and volumetric data during treatment.

RESULTS

Nine ablations were performed on 5 tumors, 2 of which had multiple recurrences. The average pretreatment lesion volume was 8.4 ± 6.3 cm3, and the average largest 2D area was 5.3 ± 2.7 cm2. The averaged TDE was 3.9 ± 2.1 cm2, average PAA was 80.1% ± 34.3%, and average PVA was 64.4% ± 23.5%. For subtotal ablations, average recurrence time was 4.4 ± 5.3 months; 1 adult case remains recurrence-free at 40 months. Using TDEs, the correlation between recurrence time and PAA was r = 0.93 (p = 0.01), and for PVA was r = 0.88 (p = 0.02). Furthermore, PVA and PAA were strongly correlated (r = 0.88, p = 0.02).

CONCLUSIONS

Through using the PAA, the real-time TDE correlated with the volume of ablation in this initial investigation. Furthermore, the TDE and volumetric data corresponded to the level of tumor control, with time to recurrence dependent on ablation completeness. MRgLITT may have a role in the management of recurrent ependymomas, especially with recent software advances.