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Session: Poster session II
Session starts: Thursday 24 January, 16:00

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Daniel de Jong (research assistant)
R.A.M. Canters ()
J. van der Zee ()
Gerard van Rhoon ()

Abstract:
Background: In hyperthermia treatment of cancer, phased-array applicators are used to heat the tumor to 40..44 degC. Nowadays advanced algorithms are used to calculate applicator settings resulting in best predicted heating of tumor tissue [1]. However, the advanced strategies will become less effective if they are not properly transferred into the clinic. Practical issues, such as mutual radiation impedance in phased arrays are influenced by patient movement, which changes the electromagnetic field (EM field). Also, impedance matching networks used in dipole antenna systems, may change in time due to heating and vary between antennas. Therefore, current standards. i.e. measuring S11-parameters at the feed points of the antennas are not always reliable indicators of the applied EM field during treatment. Methods: In order to control the EM field in annular phased-arrays, the complex field will be measured at fixed points in between the antennas and subsequently matched to the modeled (optimized) EM field. To this end, a sensor is built based on a vertical-cavity surface-emitting laser (VCSEL). This type of laser is commonly used in fiber-optic communication and can be used to measure EM fields with time domain info. To overcome measurement threshold, the EMF probe (VCSEL) is forward biased by power generated by a single-junction (silicon) solar cell, which is illuminated by an external laser diode transmitting the light along an optical fiber. The EMF probe responds to the applied EM field by emitting coherent light down a second fiber which is detected by optical receivers adjacent to the powering laser. Results: First tests in the 77-100 MHz range have shown promising results. The sensor offers high spatial resolution and measures both phase and amplitude in EM fields from 1000 down to 1 V/m. Because of its full optical operation, small size and limited use of metal material, perturbation of the EM field is expected to be small. The prototype sensor is used to measure the EM field inside a hyperthermia applicator (-60) for model validation. Results with respect to phase information showed good agreement with modeled data. Amplitude measurements could not be compared so far, because the forward bias changed during the measurement due to fiber bending. A second prototype is in development in which fiber bending should give no problems. Conclusion: The optical powered sensor is a good low cost solution for measuring complex EM fields in aqueous media. References: 1. RAM Canters, MM Paulides, MF Franckena, J van der Zee, GC van Rhoon, ”Implementation of treatment planning in the routine clinical procedure of regional hyperthermia treatment of cervical cancer: An overview and the Rotterdam experience”, Int. J. Hyperthermia, Vol. 28, pp. 570-581, (2012) - This work is supported by the Dutch Cancer Society, Grant EMCR2009􀀀4448 -