Infrared camera based thermometry for quality assurance of superficial hyperthermia applicators

Abstract

The purpose of this work was to provide a feasible and easy to apply phantom-based quality assurance (QA) procedure for superficial hyperthermia (SHT) applicators by means of infrared (IR) thermography. The VarioCAM hr head (InfraTec, Dresden, Germany) was used to investigate the SA-812, the SA-510 and the SA-308 applicators (all: Pyrexar Medical, Salt Lake City, UT, USA). Probe referencing and thermal equilibrium procedures were applied to determine the emissivity of the muscle-equivalent agar phantom. Firstly, the disturbing potential of thermal conduction on the temperature distribution inside the phantom was analyzed through measurements after various heating times (5-50 min). Next, the influence of the temperature of the water bolus between the SA-812 applicator and the phantom's surface was evaluated by varying its temperature. The results are presented in terms of characteristic values (extremal temperatures, percentiles and effective field sizes (EFS)) and temperature-area-histograms (TAH). Lastly, spiral antenna applicators were compared by the introduced characteristics. The emissivity of the used phantom was found to be ε = 0.91 ± 0.03, the results of both methods coincided. The influence of thermal conduction with regard to heating time was smaller than expected; the EFS of the SA-812 applicator had a size of (68.6 ± 6.7) cm(2), averaged group variances were ±3.0 cm(2). The TAHs show that the influence of the water bolus is mostly limited to depths of <3 cm, yet it can greatly enhance or reduce heat generation in this regime: at a depth of 1 cm, measured maximal temperature rises were 14.5 °C for T Bolus = 30 °C and 8.6 °C for T Bolus = 21 °C, respectively. The EFS was increased, too. The three spiral antenna applicators generated similar heat distributions. Generally, the procedure proved to yield informative insights into applicator characteristics, thus making the application of an IR camera a very useful tool in SHT technical QA.

Biophysical and photobiological basics of water-filtered infrared-A hyperthermia of superficial tumors

“…In order to monitor wIRA-induced heating of this novel phantom, a thermography camera (VarioCAM hr head 400, Infra Tec, Dresden, Germany) was used [52]. To assess correct absolute temperature readings, the emission coefficient of the phantom was measured (e ¼ 0.91 at 40 C), allowing for direct data collection from the entire phantom surface.…”

Using a conformal water bolus to adjust heating patterns of microwave waveguide applicators

“…4,5 In the years following those early negative trials, there has been considerable development of new heating, thermometry, and treatment planning systems capable of significantly improved control of heat delivery. [6][7][8][9][10][11][12] In addition, there has been a continual updating of quality assurance (QA) procedural guidelines intended to improve treatment quality, [13][14][15] including six QA guidelines in the 1980s, eight QA documents in the 1990's, five QA publications in the 2000's, and three guidelines currently in the journal submission cycle. Despite all this development activity, there remains only one clinical microwave hyperthermia system approved by the FDA for superficial hyperthermia in the US and that system was approved prior to the published hyperthermia trials.…”

An MR-compatible antenna and application in a murine superficial hyperthermia applicator

“…The antenna was based on an earlier designed Yagi-Uda arrangement [13]. To prevent power losses due to reflections at the point where the feed lines cross the air-water interface ( Figure 1), the feed lines were embedded within the PCB.…”

“…It presents a novel antenna design that allows superficial (this article) and deep (further study) HT under MR-control. Our concept is based on an MR-transparent Yagi-Uda antenna that was designed for the human H&N region [13]. This design was modified by applying embedded feed lines to make the antenna robust to construction tolerances, which are more prominent at 2.45 GHz compared to our previous work at 433 MHz.…”