Quantitative, Multi-institutional Evaluation of MR Thermometry Accuracy for Deep-Pelvic MR-Hyperthermia Systems Operating in Multi-vendor MR-systems Using a New Anthropomorphic Phantom

Abstract

Clinical outcome of hyperthermia depends on the achieved target temperature, therefore target conformal heating is essential. Currently, invasive temperature probe measurements are the gold standard for temperature monitoring, however, they only provide limited sparse data. In contrast, magnetic resonance thermometry (MRT) provides unique capabilities to non-invasively measure the 3D-temperature. This study investigates MRT accuracy for MR-hyperthermia hybrid systems located at five European institutions while heating a centric or eccentric target in anthropomorphic phantoms with pelvic and spine structures. Scatter plots, root mean square error (RMSE) and Bland–Altman analysis were used to quantify accuracy of MRT compared to high resistance thermistor probe measurements. For all institutions, a linear relation between MRT and thermistor probes measurements was found with R2 (mean ± standard deviation) of 0.97 ± 0.03 and 0.97 ± 0.02, respectively for centric and eccentric heating targets. The RMSE was found to be 0.52 ± 0.31 °C and 0.30 ± 0.20 °C, respectively. The Bland-Altman evaluation showed a mean difference of 0.46 ± 0.20 °C and 0.13 ± 0.08 °C, respectively. This first multi-institutional evaluation of MR-hyperthermia hybrid systems indicates comparable device performance and good agreement between MRT and thermistor probes measurements. This forms the basis to standardize treatments in multi-institution studies of MR-guided hyperthermia and to elucidate thermal dose-effect relations.

A multi-institution study: comparison of the heating patterns of five different MR-guided deep hyperthermia systems using an anthropomorphic phantom

“…The proton resonance frequency shift (PRFS) method was used to calculate MR-based thermal maps [17,24,[46][47][48], which are a dataset of MR temperatures that can be quantitatively compared with direct temperature measurements (in C). MR temperatures are deduced from phase differences (corrected for B0 drift) between the baseline scan and the actual scan.…”

“…Closed-tip sterile catheters were positioned inside and around the bone structure to facilitate the insertion of high-resistance thermistor probes, as shown in Figure 2. Further details of the phantom construction can be found in Curto et al [24]. The phantom shell was filled with a mixture of sodium benzoate, agar, and deionized water (10 g sodium benzoate and 20 g agar per 1000 g deionized water).…”

“…Only one measurement can be performed per phantom per day due to the need to cool down and stabilize the temperature of the phantom; therefore, two phantoms were produced. One of the phantoms was used to evaluate focus-steering for a centric target and the other phantom was used to evaluate focussteering for an eccentric target [24].…”

“…To make the first inventory of the performance of the five different MR-hybrid BSD2000-3D systems installed in Europe, we initiated two studies. The first study focused on performing a quantitative evaluation of the differences between the temperatures measured by MRT and thermistor probes and is reported in Curto et al [24]. The current, i.e.…”

“…Several authors have evaluated the performance of specific non-MR-compatible BSD-2000 [28,29] and BSD-2000-3D [24,30,31] applicators. Previously, the Charit e Berlin hyperthermia group reported the results of their QA testing in an MR-HT hybrid system using a cylindrical phantom and an inhomogeneous elliptical phantom containing a skeleton.…”