PARENT SESSION
1:30 PM to 3:30 PM
Monday, April 22, 2002
Poster Session 3 Heating Devices and High Temperature Therapy
Room: Nevada 1-2
(MP03-28) Assessing the reproducibility of the measurement of the sar distribution of a sigma-60 applicator in a homogeneous cylindrical phantom using the schottky diode sheet.
van Rhoon, Gerard*,1, van den Biggelaar, Adri1, Ameziane, Ali1, Rietveld, Paul1, van der Zee, Cobi1, 1 University Hospital Rotterdam-Daniel, Rotterdam, The Netherlands
ABSTRACT-
Purpose: In view of the continuous growing demand to optimize the SAR distribution in the patient, the ability to reproduce a previously induced or theoretically predicted SAR distribution is of major concern for quality assurance. Conformation and quantitative assessment of the 3D-SAR reproducibility of the Sigma-60 applicator is until now an untouched subject. Material & Methods: The Schottky diode sheet system enables us to perform on-line SAR measurement and perform parameter studies to assess the influence of variations in the Sigma-60 applicator positioning on the reproducibility of the measured SAR distribution in a homogeneous abdomen equivalent cylindrical phantom. The cumulative effect of the following parameters: power on/off, emptying bolus, sliding the applicator, lower/rise the phantom, remove/replace the phantom, rebuilding the set-up and temperature rise of the phantom on the reproducibility of the SAR distribution was investigated. Results and conclusions: The variation within a series of measurements to study the effect of a particular parameter was as expected rather small: ±4% (1 sd) for V2 and ±2% (1sd) for the effective field size (EFS). A large effect was seen for the maximum V2 for repositioning (lower/rise) the phantom: a drop by 22%. This effect was however not reflected in the measured EFS for the same experiment which changed less then 6%. The most dramatic effect was noticed for the temperature increase of the phantom tissue: V2 decreases with 3% per °C. Again, for the EFS this effect was smaller: 0.13% per °C and 1.3% per °C for temperatures ≤30 °C and >30 °C, respectively. Conclusions: The procedure in these experiments was to perform first a series of measurements of the SAR distribution with the power off/on parameter and secondly a series of measurements to investigate the cumulative effect of the additional parameters. A temperature increase of the phantom could not be avoided in all second series of experiments and hence the variation in V2 and EFS is mainly a reflection of the temperature increase. Therefore, the reproducibility of the SAR measurement of the Sigma-60 applicator is estimated to be <±5%. Acknowledgement: This work was supported by the Dutch Cancer Society: grant 97-1497.
KEYWORDS: Regional hyperthermia, Quality assurance, SAR measurement