Characteristics and performance evaluation of the capacitive Contact Flexible Microstrip Applicator operating at 70 MHz for external hyperthermia

Figures & data

Figure 1. The capacitive Contact Flexible Microstrip Applicator, CFMA-70.

Figure 2. Schematic representation of the mechanical construction of the CFMA-70 and its water cooling circuit.

Figure 3. Schematic representation of the experimental set-up used for measurement of the E-field pattern emanating from the CFMA-70. The elliptical phantom (cross section 24 cm × 36 cm, length 84 cm) has a 2-mm PVC wall and is filled with a saline solution. In the lower-right transparent representation the scanning planes are visualised.

Figure 4. Contour plots of the E-field pattern emanating from the CFMA-70 applicator with a 1-cm thick bolus. The Z-component of the E-field in the origin of the phantom is normalised to 100%. Top graph: Z-component of the E-field in the XY-plane; Middle: Z-component of the E-field in the YZ-plane; Bottom: Y-component of the E-field in the YZ-plane. For all graphs the interval between contour lines is 50 and 25 for contours above and below 100 respectively.

Figure 5. Contour plots of the SAR patterns in the XY-plane and YZ-plane emanating from the CFMA-70 applicator with a 1-cm thick bolus. The SAR is normalised to 100% at 1 cm depth in the saline solution below the centre of the applicator.

Figure 6. PDSAR profiles, SAR as a function of distance below the phantom surface, for CFMA-70 and waveguide. Profiles are given for two different saline solutions. The CFMA-70 has been positioned on the top of the phantom surface (low curvature) as well as on its side (higher curvature). The SAR is normalised to 100% at 1 cm depth in the saline solution.

Figure 7. Contour plots of the E-field pattern emanating from a 70 MHz waveguide with a 4-cm thick bolus. The Z-component of the E-field in the origin of the phantom is normalised to 100%. Top graph: Z-component of the E-field in the XY-plane; Middle: Z-component of the E-field in the YZ-plane; Bottom: Y-component of the E-field in the YZ-plane. For the top and middle graphs the interval between contour lines is 50 and 25 for contours above and below 100 respectively. For the bottom graph the interval between contour lines is 10.

Figure 8. Contour plots of the SAR pattern in the XY-plane and YZ-plane emanating from the 70 MHz waveguide with a 4-cm thick bolus. The SAR is normalised to 100% at 1 cm depth in the saline solution below the centre of the applicator.

Figure 9. Example of clinical application. CT-slice of the breast with a schematic representation of applicator and additional bolus. The applicator and bolus are kept in position using a belt around the thorax. Note the two catheter tracks in the breast for placement of thermocouple probes (third track not visible in this CT-slice).

Table I.  Properties of the CFMA-70 and CFMA-434 applicators. Data regarding the CFMA-434 is taken from Lamaitre et al. [7].

		CFMA-70	CFMA-434 3H	CFMA-434 5H
Aperture (cm × cm)	∥ × ⊥	29.5 × 20.0	28.7 × 20.7	19.7 × 29.5
EFStorso (cm × cm)	∥ × ⊥	26 × 14^†/20^‡	–	–
EFSmuscle (cm × cm)	∥ × ⊥	–	17.7 × 17.5	12.5 × 24.0
EHDtorso (cm)	top	3.4	–	–
	side	4.6	–	–
EHDmuscle (cm)	flat	–	1.4	1.4
	top	2.8	1.9	–
	side	3.4	2.4	–
RTOG 25% muscle (cm)	top	5.3	3.3	–

All measurements with the CFMA-70 have been done on an elliptical phantom with a 2-mm PVC wall and a water bolus thickness of approximately 1 cm. For the CFMA-434 applicators a flat-surfaced muscle equivalent phantom with a 1-cm fat-equivalent layer and a 1.5-cm water bolus was used for measurement of the EFS. The EHD for the CFMA-434 applicators has been measured in a flat-surfaced phantom (1-cm fat-equivalent layer and 1.5-cm water bolus) as well as in a body-shaped elliptical phantom (1-cm fat-equivalent layer and a 1-cm water bolus). The subscripts ‘muscle’ and ‘torso’ indicate whether the dielectric properties of the phantom fluid mimics muscle tissue or a tissue whose properties equal the volume average of the tissues within the human torso. The EFS is given for directions parallel and perpendicular to the major E-field, indicated respectively with ∥ and ⊥. Some measurements on the elliptical phantom have been performed with the applicator on top of the phantom (moderate curvature, see Figure 3) and also positioned against its side (higher curvature). For the CFMA-70 the EFS in the direction perpendicular to the major E-field is limited by the size of the phantom. Therefore it is given not only at 1 cm depth^†, but also at 3 cm depth^‡ (at this depth the 50% SAR intersects with the phantom edge).

Lamaitre G, Van Dijk JDP, Gelvich EA, Wiersma J, Schneider CJ. SAR characteristics of three types of contact flexible microstrip applicators for superficial hyperthermia. Int J Hyperthermia 1996; 12: 255–269

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