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Byung-Euk Joo, Sang-Ku Park, Kyung-Rae Cho, Doo-Sik Kong, Dae-Won Seo and Kwan Park

OBJECTIVE

The aim of this study was to define a new protocol for intraoperative monitoring (IOM) of brainstem auditory evoked potentials (BAEPs) during microvascular decompression (MVD) surgery to treat hemifacial spasm (HFS) and to evaluate the usefulness of this new protocol to prevent hearing impairment.

METHODS

To define the optimal stimulation rate, estimate the number of trials to be averaged, and identify useful warning criteria in IOM of BAEPs, the authors performed a preliminary study of 13 patients with HFS in 2010. They increased the stimulation rate from 10.1 Hz/sec to 100.1 Hz/sec by 10-Hz increments, and they elevated the average time from 100 times to 1000 times by 100-unit increments at a fixed stimulus rate of 43.9 Hz. After defining the optimal stimulation rate and the number of trials that needed to be averaged for IOM of BAEPs, they also identified the useful warning criteria for this protocol for MVD surgery. From January to December 2013, 254 patients with HFS underwent MVD surgery following the new IOM of BAEPs protocol. Pure-tone audiometry and speech discrimination scoring were performed before surgery and 1 week after surgery. To evaluate the usefulness of the new protocol, the authors compared the incidence of postoperative hearing impairment with the results from the group that underwent MVD surgery prior to the new protocol.

RESULTS

Through a preliminary study, the authors confirmed that it was possible to obtain a reliable wave when using a stimulation rate of 43.9 Hz/sec and averaging 400 trials. Only a Wave V amplitude loss > 50% was useful as a warning criterion when using the new protocol. A reliable BAEP could be obtained in approximately 9.1 seconds. When the new protocol was used, 2 patients (0.8%) showed no recovery of Wave V amplitude loss > 50%, and only 1 of those 2 patients (0.39%) ultimately had postoperative hearing impairment. When compared with the outcomes in the pre-protocol group, hearing impairment incidence decreased significantly among patients who underwent surgery with the new protocol (0.39% vs 4.02%, p = 0.002). There were no significant differences between the 2 surgery groups regarding other complications, including facial palsy, sixth cranial nerve palsy, and vocal cord palsy.

CONCLUSIONS

There was a significant decrease in postoperative hearing impairment after MVD for HFS when the new protocol for IOM of BAEPs was used. Real-time IOM of BAEPs, which can obtain a reliable BAEP in less than 10 seconds, is a successful new procedure for preventing hearing impairment during MVD surgery for HFS.

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Min Ho Lee, Kyung Hwan Kim, Kyung Rae Cho, Jung Won Choi, Doo-Sik Kong, Ho Jun Seol, Do-Hyun Nam and Jung-Il Lee

OBJECTIVE

Fractionated Gamma Knife surgery (FGKS) has recently been used to treat large brain metastases. However, little is known about specific volume changes of lesions during the course of treatment. The authors investigated short-term volume changes of metastatic lesions during FGKS.

METHODS

The authors analyzed 33 patients with 40 lesions who underwent FGKS for intracranial metastases of non–small-cell lung cancer (NSCLC; 25 patients with 32 lesions) and breast cancer (8 patients with 8 lesions). FGKS was performed in 3–5 fractions. Baseline MRI was performed before the first fraction. MRI was repeated after 1 or 2 fractions. Adaptive planning was executed based on new images. The median prescription dose was 8 Gy (range 6–10 Gy) with a 50% isodose line.

RESULTS

On follow-up MRI, 18 of 40 lesions (45.0%) showed decreased tumor volumes (TVs). A significant difference was observed between baseline (median 15.8 cm3) and follow-up (median 14.2 cm3) volumes (p < 0.001). A conformity index was significantly decreased when it was assumed that adaptive planning was not implemented, from baseline (mean 0.96) to follow-up (mean 0.90, p < 0.001). The average reduction rate was 1.5% per day. The median follow-up duration was 29.5 weeks (range 9–94 weeks). During the follow-up period, local recurrence occurred in 5 lesions.

CONCLUSIONS

The TV showed changes with a high dose of radiation during the course of FGKS. Volumetric change caused a significant difference in the clinical parameters. It is expected that adaptive planning would be helpful in the case of radiosensitive tumors such as NSCLCs or breast cancer to ensure an adequate dose to the target area and reduce unnecessary exposure of normal tissue to radiation.

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Kyung Hwan Kim, Doo-Sik Kong, Kyung Rae Cho, Min Ho Lee, Jung-Won Choi, Ho Jun Seol, Sung Tae Kim, Do-Hyun Nam and Jung-Il Lee

OBJECTIVE

Fractionated Gamma Knife radiosurgery (GKS) represents a feasible option for patients with large brain metastases (BM). However, the dose-fractionation scheme balanced between local control and radiation-induced toxicity remains unclear. Therefore, the authors conducted a dose-escalation study using fractionated GKS as the primary treatment for large (> 3 cm) BM.

METHODS

The exclusion criteria were more than 3 lesions, evidence of leptomeningeal disease, metastatic melanoma, poor general condition, and previously treated lesions. Patients were randomized to receive 24, 27, or 30 Gy in 3 fractions (8, 9, or 10 Gy per fraction, respectively). The primary endpoint was the development of radiation necrosis assessed by a neuroradiologist blinded to the study. The secondary endpoints included the local progression-free survival (PFS) rate, change in tumor volume, development of distant intracranial progression, and overall survival.

RESULTS

Between September 2016 and April 2018, 60 patients were eligible for the study, with 46 patients (15, 17, and 14 patients in the 8-, 9-, and 10-Gy groups, respectively) available for analysis. The median follow-up duration was 9.6 months (range 2.5–25.1 months). The 6-month estimated cumulative incidence of radiation necrosis was 0% in the 8-Gy group, 13% (95% confidence interval [CI] 0%–29%) in the 9-Gy group, and 37% (95% CI 1%–58%) in the 10-Gy group. Being in the 10-Gy group was a significant risk factor for the development of radiation necrosis (p = 0.047; hazard ratio [HR] 7.2, 95% CI 1.1–51.4). The 12-month local PFS rates were 65%, 80%, and 75% in the 8-, 9-, and 10-Gy groups, respectively. Being in the 8-Gy group was a risk factor for local treatment failure (p = 0.037; HR 2.5, 95% CI 1.1–29.6). The mean volume change from baseline was a 47.5% decrease in this cohort. Distant intracranial progression and overall survival did not differ among the 3 groups.

CONCLUSIONS

In this dose-escalation study, 27 Gy in 3 fractions appeared to be a relevant regimen of fractionated GKS for large BM because 30 Gy in 3 fractions resulted in unacceptable toxicities and 24 Gy in 3 fractions was associated with local treatment failure.