Quality assurance: Recommended guidelines for safe heating by capacitive-type heating technique to treat patients with metallic implants

Figures & data

Figure 1. Configuration of the computer simulation model.

Table 1.  Electrical and thermal characteristics of blood, muscle and air.

	Parameter	Blood	Muscle	Air
ρ	Density (kg/m^3)	1060	1070	1.293
C	Specific heat  (J/kg K)	3900	3500	1006
k	Thermal conductivity  (W/m K)	0.51	0.59	0.0241
ωb	Blood flow rate  at 37 °C (L/s)	–	4.82 × 10^−4	–
Ms	Metabolic rate  at 37 °C (W/m^3)	–	696	–
σ	Conductivity (S/m)	1.080	0.608	0
εr	Relative permittivity	352	203	1

Figure 2. Control model when a stent is not inserted. The entire heated substance is defined as muscle. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 2A. Each curve is the temperature profile at the heating time (min) indicated in the insert on the right. (D) Extrusion plot of temperature distribution on the red line shown in Figure 2A. Horizontal axis indicates the heating time in min. Maximum SAR 34 W/kg; maximum temperature 45.4 °C.

Figure 3. Biliary duct stent placed in horizontal direction. Lumen: vessel. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 3A. The broken line is the control, which indicates the temperature profile after heating for 20 min shown in Figure 2C. (D) Extrusion plot of temperature distribution on the red line shown in Figure 3A. Maximum SAR 328 W/kg; maximum temperature 45.6 °C.

Figure 4. Biliary duct stent placed in horizontal direction. Lumen: muscle. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profile on the red line shown in Figure 4A. The broken line is the control, which indicates the temperature profiles after heating for 20 min shown in Figure 2C. (D) Extrusion plot of temperature distribution on the red line shown in Figure 4A. Maximum SAR 392 W/kg; maximum temperature 46.2 °C.

Figure 5. Biliary duct stent placed in horizontal direction. Lumen: air. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 5A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 5A. Maximum SAR 649 W/kg; maximum temperature 46.9 °C.

Figure 6. Biliary duct stent placed in vertical direction. Lumen: vessel. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 6A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 6A. Maximum SAR 2027 W/kg; maximum temperature 45.7 °C.

Figure 7. Biliary duct stent placed in vertical direction. Lumen: air. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profile on the red line shown in Figure 7A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 7A. Maximum SAR 2525 W/kg; maximum temperature 55.2 °C.

Figure 8. Biliary duct stent placed in vertical direction. Length: 10 cm. Lumen: air. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 8A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 8A. Maximum SAR 5557 W/kg; maximum temperature 80.4 °C.

Table 2.  Excessive temperature rise when placing a biliary duct stent in the muscle and heating under various conditions.

Direction of stent	Length of stent (cm)	Material of lumen	Maximum SAR (W/kg)	Maximum temperature (°C)	Temperature difference (°C)
Control (No stent)	5	Muscle	34	45.4	0
Horizontal	5	Vessel	328	45.6	0.2
Horizontal	5	Muscle	392	46.2	0.8
Horizontal	5	Air	649	46.9	1.5
Vertical	5	Vessel	2027	45.7	0.3
Vertical	5	Muscle	2186	55.8	10.4
Vertical	5	Air	2525	55.2	9.8
Vertical	10	Air	5557	80.4	35.0

Figure 9. Oesophageal stent placed in horizontal direction. Lumen: vessel. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 9A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 9A. Maximum SAR 433 W/kg; maximum temperature 46.4 °C.

Figure 10. Oesophageal stent placed in horizontal direction. Lumen: air. (A) Cross-sectional view of the model at x = 0 cm. B: Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 10A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 10A. Maximum SAR 950 W/kg, maximum temperature 49.1 °C.

Figure 11. Oesophageal stent. Difference of levels: 4 cm. Lumen: vessel. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profiles on the red line shown in Figure 11A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 11A. Maximum SAR 1576 W/kg, maximum temperature 50.4 °C.

Figure 12. Oesophageal stent. Difference of levels: 4 cm. Lumen: air. (A) Cross-sectional view of the model at x = 0 cm. (B) Temperature distribution after heating for 20 min. (C) Temperature profile on the red line shown in Figure 12A. (D) Extrusion plot of temperature distribution on the red line shown in Figure 12A. Maximum SAR 2678 W/kg, maximum temperature 62.7 °C.

Table 3.  Excessive temperature rise when using an oesophageal stent.

Lumen of stent	Level difference between two ends of stent (cm)	Maximum SAR (W/kg)	Maximum temperature (°C)	Temperature difference (°C)
Control	–	34	45.4	0
Air	0	950	49.1	3.7
Air	2	1561	54.9	9.5
Air	4	2678	62.7	17.3
Air	6	4145	72.0	26.6
Air	Vertical	4461	76.3	30.9
Vessel	0	433	46.4	1.0
Vessel	2	831	48.0	2.6
Vessel	4	1576	50.4	5.0
Vessel	6	2630	52.8	7.4
Vessel	Vertical	3034	50.8	5.4

Table 4.  Excessive temperature rise under various heating conditions.

Use of stent	Direction	Blood flow in stent	Excessive temperature rise (°C)
Biliary duct	Horizontal	Yes	No
Biliary duct	Horizontal	No	No
Biliary duct	Vertical	Yes	No
Biliary duct	Vertical	No	∼10
Oesophageal	Horizontal	Yes	No
Oesophageal	Horizontal	No	∼4
Oesophageal	Vertical	Yes	∼7
Oesophageal	Vertical	No	∼30

Table 5.  Adverse reactions when capacitive-type heating was applied in patients having a stent (Aino Hospital).

Case ID	Disease	Site	Location of stent	Type of stent	No. of treatments	Day started	Day ended	Maximum Power (W)	Adverse reaction
89	Colon cancer Liver metastasis	Liver	Lumbar vertebra	Metal	90	23 Feb 2003	29 Aug 2005	1100	No
337	Large bowel cancer	Abdomen	Rectum	Metal	1	16 Dec 2004	16 Dec 2004	630	No
357	Intrahepatic bile duct cancer	Liver	Biliary tract	Metal	5	4 Feb 2005	24 Feb 2005	700	No
396	Pancreas head cancer	Pancreas head	Biliary tract	Metal	8	20 June 2005	15 Aug 2005	1500	No
671	Liver metastasis after operating Intraperitoneal metastasis	Abdomen	Rectum	Metal	8	13 Aug 2007	10 Oct 2007	1450	No
698	Pancreatic metastasis Liver metastasis	Pancreas	Biliary tract	Plastic	3	5 Nov 2007	19 Nov 2007	1500	No
758	Bile duct cancer Lymph node metastasis	Upper abdomen	Biliary tract	Metal	8	16 May 2008	11 July 2008	1500	No

Table 6.  Adverse reactions when capacitive-type heating was applied in patients having stents (Hospital of the University of Occupational and Environmental Health Japan).

		Heating equipment		Stent
Case ID	Disease	Diameter of electrodes	Output power	Location	Type	Length × Diameter	Level difference between two ends	Material in lumen	Adverse reaction
A	Cardiac gastric cancer	30 cm	500–600 W	Oesophagus	Metal	7 × 2.5 cm	2 cm	Air and a little liquid	No
B	Oesophageal cancer			Oesophagus	Metal	10 × 2 cm	2 cm	Air and liquid	No
C	Oesophageal cancer		800 W for 5 min → 400 W for 30 min	Oesophagus	Metal	>10 × 2.5 cm	No difference	Air and a little liquid	Smoke from mouth Vomiting of blood
D	Pancreatic carcinoma	Biliary tract			Metal	< 5 × 1 cm	No difference	Gall	No
E	Bile duct cancer		1500 W for 15 times	Biliary tract	Plastic	5 × 0.7 cm	3 cm		No