PARENT SESSION
1:30 PM to 3:30 PM
Saturday, April 20, 2002
Poster Session 1 Noninvasive Treatment Monitoring and Treatment Planning
Room: Nevada 1-2
(MP01-6) Ultrasound-guided thermometry during local hyperthermia in a rat tumor model.
Peschke, Peter*,1, Novak, Petr2, Pousek, Lubomir2, Schreib, Petr2, Debus, Jürgen1, Zuna, Ivan1, 1 Dept. of Radiation Oncology, Heidelberg, Germany2 Centre for BioMedical Engineering, Prague, Czech Republic
ABSTRACT-
Continuous temperature monitoring during local hyperthermia is a prerequiste for successful thermal therapy. The need for non-invasive monitoring modalities has arisen as a consequence of the limitations of invasive thermometry: trauma to the patient and the restricted number of measuring points. Here we describe the non-invasive measurement of temperature distributions in an experimental tumor model using ultrasound B-mode images combined with texture parameter analysis. Fresh pieces of Dunning R3327-AT1 prostate tumors were transplanted into a dorsal skin flap pedicle of male young adult Copenhagen rats. Loop controlled microwave thermotherapy was started when the tumors reached a diameter of 18±1 mm. A central tumor section was continuously imaged by ultrasound during the course of hyperthermia. Image texture parameters were analyzed in selected regions of interest (ROIs) and correlated with temperature data from invasive thermocouples. All animal experiments were performed under general gaseous anesthesia. Three different ROIs (100 x 100 pixels) from ultrasound images of heated tumors (n = 56) were analyzed. A strong correlation was found between the mean gray scale values within the ROIs and the invasively measured temperatures ranging from 37 degrees C to 44 degrees C. The correlation coefficient was r = 0.96±0.05. The temperature increase was a linear function of the mean gray level, starting at 37.0±1.18 with a slope of 0.94±0.23. The second important parameter was the mean gradient with r = 0.74±0.21. All other parameters did not show any correlation with temperature. To display information on the temperature distribution across the scanned tumor area, images were parceled (12 x 12 pixels)and the mean gray scale value was evaluated for each region. The matrix of results was used for pseudo-color coding of grayscale B-mode images. Ultrasound-guided thermometry is a useful technique for the non-invasive monitoring of temperature distributions during local tumor hyperthermia as shown in an experimental tumor model. Mean gray scale value extracted from ultrasound B-mode images provides satisfactory temperature resolution within the complete treatment volume. Work is in progress to increase the spatial resolution of the temperature distribution in three dimensions.
KEYWORDS: Thermometry, Hyperthermia, Temperature distribution, Animal tumor model