Improving locoregional hyperthermia delivery using the 3-D controlled AMC-8 phased array hyperthermia system: A preclinical study

Figures & data

Figure 1. The AMC-8 system. Left 2 × 4 waveguides during construction. Right in clinical use.

Figure 2. Transversal cross-section of the AMC-4 system/single ring set up of AMC-8 system (A) combined with the R-phantom, the sagittal midplane is indicated with a dotted line. Sagittal cross sections of the AMC-4 system (B) and the AMC-8 system (C, D) with the transversal midplane indicated with a dotted line. The 24 × 24 cm section where E-field measurements were performed shown in Figure 6 is indicated in the sagittal midplane of the R-phantom in (D). For simplicity, all images show AMC-8 ¼λ waveguides (34 × 21 × 12 cm).

Table I.  List of relevant system properties with the performance parameters and phantoms used for evaluating the properties.

System property	Parameter	Phantom
Focus size	FWHM	R-phantom
SAR ratio	RSratio	R-phantom
3-D control	Δz	R-phantom
Efficiency	SAR	E-phantom

Figure 3. Simulations showing the impact of ring distance on the normalised SAR distribution in the sagittal midplane of the R-phantom. Left: AMC-4 system (configuration 1). Right: AMC-8 system (configuration 2) with D_ring = 5 (top) and D_ring = 11 cm (bottom). SAR normalised to maximum SAR in the focus in each panel, note that the SAR level in the focus is lower for 8 than for 4 waveguides (see text). 50% iso SAR shown in bold.

Table II.  Configurations used for determining characterisation parameters FWHM, RS_ratio and Δz for the single ring or two rings set up of the AMC-8 system by using E-field distribution measurements and simulations in the R-phantom. FWHM indicates the size of the focus. RS_ratio is the normalised ratio between maximum normal tissue SAR and SAR in the focus. The SAR focus shift Δz is a measure for 3-D spatial control. Power settings of every ring are listed as the amplitude ratio between the top, bottom, left, right waveguide (t:b:l:r), respectively, with a total power of 800 W. Phase settings are listed for the top, bottom, left, right waveguide (t,b,l,r), respectively. Phase and amplitude settings of ring 2 of the AMC-8 (two rings) are identical to settings of ring 1, with the phase settings offset with φ_ring and a ring to ring distance D_ring. ^†Simulations only.

	AMC8, single ring		AMC8, two rings
Configuration	Amplitude t : b : l : r	Phase t,b,l,r	Amplitude t : b : l : r	Phase t,b,l,r	φring	Dring (cm)	Parameter
1	1 : 1 : 1 : 1	0°,0°,0°,0°					FWHM, RSratio
2^†			1 : 1 : 1 : 1	0°,0°,0°,0°	0°	2–13	FWHM, RSratio
3			1 : 1 : 1 : 1	0°,0°,0°,0°	−30°, 0°, 30°	3	Δz

Table III.  Phase and amplitude settings used for determining system efficiency EFF using SAR distribution measurements and simulations in the E-phantom. Five phase and amplitude settings were used for each of the three systems: AMC-4, AMC-8 (single ring) and AMC-8 (two rings). Power settings of every ring are listed as the amplitude ratio between the top, bottom, left, right waveguide (t:b:l:r), respectively, with a total power of 800 W. Phase settings are listed for the top, bottom, left, right waveguide (t,b,l,r), respectively. Phase and amplitude settings of ring 2 of the AMC-8 (two rings) are identical to the settings of ring 1, with the phase settings offset with φ_ring and a ring to ring distance D_ring = 3 cm.

	AMC4		AMC8, single ring		AMC8, two rings
Setting	Amplitude t : b : l : r	Phase t,b,l,r	Amplitude t : b : l : r	Phase t,b,l,r	Amplitude t : b : l : r	Phase t,b,l,r	φring
1	1 : 1 : 1 : 1	0°,0°,0°,0°	1 : 1 : 1 : 1	0°,0°,0°,0°
2	1 : 1 : 1 : 1	0°,0°,45°,45°	1 : 1 : 1 : 1	0°,0°,45°,45°	1 : 1 : 1 : 1	0°,0°,45°,45°	0°
3	3 : 3 : 2 : 2	0°,0°,45°,45°	3 : 3 : 2 : 2	0°,0°,45°,45°	3 : 3 : 2 : 2	0°,0°,45°,45°	0°
4					3 : 3 : 2 : 2	0°,0°,45°,45°	−30°
5	3 : 3 : 2 : 2	0°,0°,30°,30°	3 : 3 : 2 : 2	0°,0°,30°,30°	3 : 3 : 2 : 2	0°,0°,30°,30°	0°
6					3 : 3 : 2 : 2	0°,0°,30°,30°	−30°
7	3 : 3 : 2 : 2	0°,0°,0°,0°	3 : 3 : 2 : 2	0°,0°,0°,0°

Figure 4. R-phantom simulations of the axial (closed diamonds) and radial (open diamonds) full width half maximum FWHM of the SAR focus as a function of D_ring in the AMC-8 system (configuration 2). AMC-4 system (configuration 1) values shown for reference (squares).

Figure 5. R-phantom simulations of the RS_ratio for the AMC-8 system (diamonds, configuration 2) as a function of D_ring. AMC-4 system (configuration 1) value shown for reference (square).

Figure 6. E_z field distributions in the 24 × 24 cm section of the sagittal midplane of the R-phantom in the AMC-8 system shown in Figure 2D for configuration 3. Top row: measured E_z field distributions for φ_ring = 30° (left hand panel), φ_ring = 0° (central panel) and φ_ring = −30° (right hand panel) reconstructed from data on horizontal and vertical tracks shown. The measured focus position z_focus = 6.7 cm for φ_ring = −30°, z_focus = 1.6 cm for φ_ring = 0°, and z_focus = −2.4 cm for φ_ring = 30°. Bottom row: simulated E_z field distributions matching distributions of the top row in arbitrary units, therefore only position and extension of simulated and measured contours may be compared.

Figure 7. Heating efficiency determined by comparing measured and simulated SAR distributions in the transversal midplane of the E-phantom. Example shown for a single ring of the AMC-8 system for phase and amplitude setting 3 listed in Table III (amplitude 3 : 3 : 2 : 2, phase 0°,0°,45°,45° for top:bottom:left:right). Left: measured SAR distribution in W/kg. Right: simulated SAR distribution in W/kg, an efficiency of 64% was assumed to match the average simulated SAR to the measured SAR data in the central area (r < 10).