A feasibility study of interstitial hyperthermia plus external beam radiotherapy in glioblastoma multiforme using the multi electrode current source (MECS) system

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Abstract
Purpose: Thermoradiotherapy has been shown in several randomized trials to increase local control compared to radiotherapy alone. The first randomized study of interstitial hyperthermia in glioblastoma multiforme showed a survival benefit for hyperthermia, though small. Improvement of the heating technique could lead to improved results. The purpose of this feasibility study is to present the clinical and thermal data of application of an improved interstitial hyperthermia system. Methods and materials: Six patients with a glioblastoma multiforme were treated with interstitial hyperthermia using the Multi Electrode Current Source Interstitial Hyperthermia (MECS-IHT) system. The MECS-IHT system has the capability of spatial monitoring of temperature and individually steering of heating electrodes. Three sessions were given aiming at a steady state temperature of 42°C for 1 h, with an interval of 3–4 days, during an external irradiation scheme of 60 Gy in 6 weeks. Hyperthermia was delivered with a mean of 10 catheters, 18 heating electrodes and 38 thermal probes per patient. Results: Sub-optimal temperatures were encountered in the first two patients leading to adjustments in technique thereafter with subsequent improvement of thermal data. With a catheter spacing of 11–12 mm, measurements yielded a mean T90, T50 and T10 of 39.9, 43.7 and 45.2°C, respectively, over three sessions in the last patient. The power per electrode to reach this temperature distribution varied from 25–100% of full power in each of the last four patients. Thermal data were reproducible over the three sessions. Acute toxicity was minimal. Conclusions: Despite the spatial steering capabilities of the MECS-IHT system, a large temperature heterogeneity was encountered. The heterogeneity was the reason to limit the catheter spacing to 11–12 mm, thus making only small tumour volumes feasible for interstitial heating.

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