Image-based computer modeling assessment of microwave ablation for treatment of adrenal tumors

Figures & data

Figure 1. (A) Example CT image illustrating MWA applicator insertion path, adrenal gland, and adjacent structures. (B) computational model representing this case constructed from the segmented tissue regions and application position.

Table 1. Tissue biophysical properties employed in FEM simulation at 2.45 GHz.

Tissue	Tissue property [40–42]
	Relative permittivity ${\epsilon }_r$ [–]	Electrical conductivity $\mathrm{\sigma }$ [S/m]	Volumetric heat capacity $\rho c$ [J/m^3/K]	Thermal conductivity $k$ [W/m/K]	Blood perfusion rate $m$bl [kg/m^3/s]
Adrenal gland	58	1.07	3.61 $\times$ 10^6	0.44	26.8
Adrenal tumor (APA)	32.4	1.2	3.82 $\times$ 10^6	0.52	26.8
Fat	10.8	1.75	2.14 $\times$ 10^6	0.52	0.6
Kidney	52.7	2.43	4.01 $\times$ 10^6	0.53	69.7
Blood vessel*	58.3	2.54	3.79 $\times$ 10^6	0.52	12.5
Stomach	62.2	2.21	4.01 $\times$ 10^6	0.53	8.5
Liver	43	1.69	3.82 $\times$ 10^6	0.52	15.8
Spine**	11.4	0.394	2.68 $\times$ 10^6	0.32	0.18
Spleen	52.4	2.24	3.92 $\times$ 10^6	0.53	28.6
Small Intestine	53.9	2.04	3.76 $\times$ 10^6	0.54	14.2
Muscle	44	1.75	3.82 $\times$ 10^6	0.52	0.55

*Aorta, vena cava, other large vein. **Modeled as cortical bone.

Table 2. Acceptable volumes of collateral damage in different organs.

Organ	V [mm³]
Spine	2000
Liver	1000
Stomach	0
Kidney	1000
Spleen	0
Small veins	1000
Aorta*	0
Vena Cava*	0
Other*	0

*A value of 0 mm³ indicates no ablation to the structures was considered acceptable.

Table 3. Summary data for 14 simulated APA microwave ablation cases and ablation boundary estimated by threshold of 240 CEM43.

Case	APA volume [mm³]	Stopping criterion	Ablation time [s]	Total volume of ablated tissue. [mm^3]	Fraction of APA ablated [%]	Short axis [mm]	Long axis [mm]	Height [mm]	Thermally affected organs/regions
1	650	Saturation	270	3,877	90	16.8	17.5	26.6	Gland: 9.7% Kidney: 242 mm³
2	393	Organ at risk	90	1,484	58	11.9	13.3	21.0	Gland: 13.9% Kidney: 324 mm³
3	628	Saturation	240	3,701	94	23.1	21.7	26.6	Gland: 12.8% Veins: 27 mm³
4	1,905	–	600	2,500	80	14.0	15.4	21.7	Gland: 0.6% Liver: 181 mm³
5	448	Saturation	390	2,657	88	14.7	14.0	21.0	Gland: 16.5% Kidney: 399 mm³ Veins: 2 mm³
6	883	Organ at risk	120	2,230	78	16.8	16.8	24.5	Gland: 5.9% Veins: 86 mm³
7	1,872	Organ at risk	90	1,875	30	14.7	16.8	22.4	Gland: 3.7% Veins: 98 mm³
8	2,078	Saturation	540	10,065	75	24.5	25.2	32.2	Gland: 13.8%
9	1,600	Organ at risk	360	3,141	71	18.2	16.8	21.7	Gland: 16.5% Liver: 1.1 mm³ Kidney: 29 mm³
10	995	Organ at risk	90	1,553	38	13.3	14.0	20.3	Gland: 5.3% Kidney: 24 mm³ Veins: 31 mm³
11	2,395	Organ at risk	540	5,823	65	21.7	20.3	28.7	Gland: 3.6% Liver: 997 mm³
12	995	Organ at risk	60	981	62	12.6	13.3	19.6	Gland: 2.3% Veins: 1 mm³
13	1,659	–	600	11,328	81	25.2	25.9	34.3	Gland: 16.3% Bone: 4 mm³
14	985	Organ at risk	120	3,124	66	19.6	22.4	30.1	Gland: 8.4%
Average	1249 ± 654		293.6 ± 208	3881 ± 3142	70 ± 19	17.6 ± 4.5	18.1 ± 4.3	25.0 ± 4.8

Figure 2. Specific absorption rate in tissues near applicator in (A) radial, and (B), (C) longitudinal (B), (C) slices along the applicator (white space) as well as D) 3D visualization of applicator (blue), tumor (temperature map), kidney (beige), spine (white) and other (purple) with SAR map overlaying tumor volume.

Figure 3. Temperatures in tissues near applicator in (A) radial, and (B), (C) longitudinal (B), (C) slices along the applicator (white space) as well as (D) 3D visualization of applicator (blue), tumor (temperature map), kidney (beige), spine (white) and other (purple) with temperature map overlaying tumor volume.

Figure 4. Thermal profiles for case 10 at the termination time of t = 90 s. The ablation applicator axis is approximately perpendicular to the long axis of the tumor, resulting in substantial fraction of the ablation zone extending beyond the target in one direction, but lateral extents of the target volume remaining unablated. The ablation duration is limited by unacceptable collateral damage in structures like the adjacent pancreas and intestines (see Table 2).

Figure 5. Illustration of the impact of applicator positioning relative to the adrenal gland on thermal profiles. (A) Applicator is approximately 1.5 mm away from the adrenal gland/tumor, separated by a layer of peri-adrenal fat (tumor coverage: ∼48%) (B) The applicator is adjacent to the adrenal gland/tumor boundary (tumor coverage: ∼79%).