SAR characteristics of the Sigma-60-Ellipse applicator

Figures & data

Figure 1. The Sigma-60-Ellipse phased array applicator and the cylindrical PVC phantom as placed in the measurement set-up (A), schematic representation of the phantom and place of the E-field sheets on the lower-half split of the phantom (B), a photo of the Schottky diode E-field sheet (C), the top view of two Schottky diode sheets with position of the diodes (D), and schematic representation of the measurement set-up (E).

Figure 2. Schematic representation of the opening of the three applicators and their central dimensions (A), the contour plot of SAR-distribution (B), the profile of the SAR-distribution along the fourth row (C), and the tenth column of the Schottky diode sheets (D). The exposure to the phantom was applied in target position of (0, 0) cm, 800 W total power, 100% amplitude, and a frequency of 100 MHz.

Figure 3. Examples of the contour plot of SAR distributions for the Sigma-60-Ellipse applicator at different frequencies, 800 W total power, (0, 0) cm target position, and 100% amplitude.

Figure 4. Average measurements of the Sigma-60-Ellipse applicator as function of frequency at 400 and 800 W total power, (0, 0) cm target position, and 100% amplitude: 50% iso-SAR area (A), 50% iso-SAR longitudinal length (LL50) along the rows 4 and 5 (B), and 50% iso-SAR radial length (RL50) along the columns 8 and 10 of the Schottky diode sheets (C).

Table I.  Comparison between requested and measured target position for the Sigma-60-Ellipse applicator at different frequencies, total power of 800 W, and 100% amplitude.

	Average measured (Z, X) cm at frequency of
Requested (Z, X) cm	77 MHz	100 MHz	120 MHz
0, −8.0	−1.1, −6.6	0.5, −7.7	0.9, −8.8
0, −6.0	−1.0, −6.2	0.9, −5.9	−2.2, −5.8
0, −4.0	−0.9, −5.3	1.3, −4.0	−3.0, −3.8
0, −2.0	−0.7, −1.9	1.3, −2.2	−0.9, −1.6
0, 0.0	−0.3, −0.4	−2.0, −0.4	−0.8, −0.3
0, 2.0	−0.6, 4.3	2.4, 2.3	−2.2, 2.1
0, 4.0	−0.4, 5.2	1.4, 4.1	−2.4, 4.7
0, 6.0	−0.5, 6.3	0.9, 5.3	−1.0, 6.1
0, 8.0	−1.4, 6.6	0.3, 6.9	−0.9, 7.8

Table II.  Characteristic values of the Sigma-60, the Sigma-Eye, and the Sigma-60-Ellipse applicators describing the SAR distribution as a function of frequency at 800 W total power, (0, 0) cm target position, and 100% amplitude. The results for the Sigma-60-Ellipse are average of 3-4 measurements. Numbers in parentheses show 1SD.

	Applicator
Frequency	LL50* (cm)			RL50* (cm)			Calculated 50% iso-SAR area (cm^2) as an ellipse from LL50 and RL50
(MHz)	S-60^†	S-Eye^†	S-60-Ellipse	S-60	S-Eye	S-60-Ellipse	S-60	S-Eye	S-60-Ellipse
75	20.9		21.6(0.1)	15.3		14.9(0.3)	251		252
80	21.4		20.9(0.9)	13.8		13.2(1.2)	232		216
90	21.7		21.2(0.8)	12.4		11.9(1.0)	211		198
100	19.6	22.5	21.5(1.1)	9.7	10.5	10.5(0.5)	149	186	176
110	19.1		22.2(0.9)	9.2		9.1(0.8)	138		159
120	18.6		21.1(0.3)	8.2		8.5(0.3)	120		140

*The LL50 and RL50 are defined as 50% iso-SAR longitudinal and radial length, respectively. ^†The data presented for the Sigma-60 and the Sigma-Eye applicators are from van Rhoon et al. [11], [18], [19].

Table III.  Physical comparison of the Sigma-60, the Sigma-Eye, and the Sigma-60-Ellipse applicators as provided by the BSD Medical Corporation [12].

	Sigma-60	Sigma-Eye	Sigma-60-Ellipse
Frequency range (MHz)	60–120	100	80–110
Antenna length (cm)	45	14	45
Array/diameter max. (cm)	58	38 × 53	37 × 53
Bolus-patient contact length (cm)	∼36	∼50	∼50
Drive ports	4	12	4
Radiators	8	24	8
E-field alignment	Long axis	Long axis	Long axis
Convergent mode	2D TEM*	3D TEM	D TEM

*TEM: transverse electro magnetic.

Van Rhoon GC, van der Heuvel DJ, Ameziane A, Rietveld PJM, Volenec K, van der Zee J. Characterization of the SAR-distribution of the Sigma-60 applicator for regional hyperthermia using a Schottky diode sheet. Int J Hyperthermia 2003; 19: 642–654

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Van Rhoon GC, Ameziane A, van der Biggelaar A, Riteveld PJM, van der Zee J. Assessment of the SAR steering feasibility of the Sigma-Eye applicator using the Schottky diode sheet. Annual meeting of the Radiation Research Society & North American Hyperthermia Society. Reno, USA 2001

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Van Rhoon GC, Ameziane A, Abdel-Rahman S, Futschik G, Turner PF, Hagmann M, Issels RD. SAR characteristics of six different Sigma-Eye applicator configurations in homogeneous clinical phantom using the Schottky diode sheet a multi-institutional study. Annual meeting of the Radiation Research Society & North American Hyperthermia Society. Reno, USA 2002

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BSD-2000 Function and Operations. BSD Medical Corporation Report 2004. 22–23

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