Prospective treatment planning to improve locoregional hyperthermia for oesophageal cancer

Figures & data

Table I.  Values of the dielectric and thermal properties used in the simulations, for different tissue types at 70 MHz and under hyperthermia conditions; conductivity (σ(S m⁻¹)), relative permittivity (ε_r (−)), density (ρ (kg m⁻³)), specific heat capacity (c (J kg⁻¹°C⁻¹)), thermal conductivity (k (W m⁻¹°C⁻¹)) and perfusion (W_b (kg m⁻³ s⁻¹)).

	σ (S m^−1)	εr (−)	ρ (kg m^−3)	c (J kg^−1°C^−1)	k (W m^−1°C^−1)	Wb (kg m^−3 s^−1)
Air	0	1	1.29	10 000*	0.024	0
Aorta	0.83	75	1025	3 740	0.58	–
Bone	0.05	10	1595	1 420	0.65	0.12
Fatty tissue	0.06	10	888	2 387	0.22	1.1
Heart	0.95	93	1025	3 740	0.58	–
Lung	0.2	20	750	3 000	0.25	3.6
Muscle-like	0.75	75	1050	3 639	0.56	3.6
Spinal cord	0.32	53	1050	3 639	0.56	3.6
Tumour	0.74	65	1050	3 639	0.56	1.8

* The value of c used for air was 10-times too high in order to allow larger time steps in thermal computations. The effect on the steady state temperature is negligible (<2×10⁻⁵°C).

Figure 1. Patient set up in the 70 MHz AMC-4 phased array locoregional hyperthermia system during treatment (left) and a schematic representation of the applied thermometry (right).

Figure 2. The power pulse scheme for the ΔT-measurements applied at the start of each treatment. The units along the vertical axes are arbitrary (a.u.).

Figure 3. Example of the patient's dorsoventral (AP) and lateral (LAT) diameters, determined from the CT scan in treatment position. The location of the tumour is marked as ‘t’.

Table II.  Example of calculated, clinical and mixed power ratios (P) and phase settings (Φ) for patient 12, normalized to the top antenna. The top antenna is the reference, i.e. phase 0°.

	Ptop	Pbottom	Pleft	Pright	Φtop	Φbottom	Φleft	Φright
Calculated	1	1.84	0.47	1.29	0°	26°	−47°	24°
Clinical	1	3	3	3	0°	0°	10°	20°
Mixed	1	1.84	0.47	1.29	0°	0°	10°	20°

Figure 4. Transversal, coronal and sagittal slices of the numerically optimized temperature distribution and the corresponding anatomy of patient 12. The tumour temperature was maximized, taking constraints of 42°C to normal tissue and 40°C to the spinal cord into account.

Table III.  Results of ΔT-measurements performed with calculated, clinical and mixed settings, averaged over 48 treatments (mean ± SEM) in 16 patients.

	ΔToes	ΔTcord	ΔToes/ΔTcord
Calculated	0.36 ± 0.02°C*	0.29 ± 0.02°C	1.3 ± 0.09
Clinical	0.38 ± 0.03°C*	0.23 ± 0.02°C*	1.7 ± 0.15
Mixed	0.48 ± 0.04°C	0.33 ± 0.02°C	1.5 ± 0.12

* Significantly different from values measured with mixed settings (p < 0.05).

Table IV.  The clinically measured (M) and computed (C) ratios ΔT_oes/ΔT_cord for patient 12, resulting from the calculated, clinical and mixed settings. The simulated steady state tumour temperatures T₁₀, T₅₀ and T₉₀ are also listed, together with the maximum temperature in normal tissue (T_max) and the temperature in the back musculature, near the spinal cord (T_cord).

	ΔToes/ΔTcord = ratio (M)	ΔToes/ΔTcord = ratio (C)	T10	T50	T90	Tmax	Tcord
Calculated	0.49/0.25 = 2.0	0.89/0.37 = 2.4	42.2	41.2	39.5	43.2	41.0
Clinical	1.16/0.23 = 5.0	0.94/0.27 = 3.5	42.2	41.2	39.4	45.1	39.9
Mixed	1.04/0.31 = 3.4	0.97/0.35 = 2.8	42.5	41.5	39.5	44.9	40.8

Figure 5. Transversal slices of the steady state temperature distribution of patient 12 resulting from the calculated, clinical and mixed settings as well as the steady state temperature distribution resulting from the settings prescribed by optimization on ΔT-ratio. In all cases, the total power was normalized to the amount applied in the clinic (800 W).