Predictive value of simulated SAR and temperature for changes in measured temperature after phase-amplitude steering during locoregional hyperthermia treatments

Figures & data

Table 1. Values of the electrical and thermal tissue properties at 70 MHz used in the simulations.

	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	1000	0.024	0
Bone	0.05	10	1595	1420	0.65	0.12
Fat	0.06	10	888	2387	0.22	1.1
Muscle	0.75	75	1050	3639	0.56	3.6
Tumor	0.74	65	1050	3639	0.56	1.8

Electrical 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]) [20,33].

Figure 1. The different steps of the analysis to determine linear correlations between measured changes in temperature and simulated changes in SAR or temperature after phase-amplitude steering.

Figure 2. Flow chart of the event selection process, representing the excluded treatment sessions, events, and measurements. Note that multiple events can occur in one treatment session and that measurements were evaluated for each individual event.

Table 2. Summary of the numbers finally included in the analysis.

Numbers for final analysis
38 patients	23 cervix/vagina tumors
	14 bladder tumors
	1 vulva
60 treatment sessions	34 cervix/vagina tumors
	25 bladder tumors
	1 vulva
67 phase-amplitude steering events	43 amplitude adaptations
	24 phase adaptations
124 measurements	38 vagina
	41 bladder
	45 rectum

Table 3. Median, minimum and maximum values of the measured temperature and (unscaled) simulated temperature and SAR, averaged over the thermocouple probe trajectory per location. Values were taken at the time of the phase-amplitude steering event. The last column indicates the total amount of power.

Tumor site	Location	Median measured temperature (°C) (min;max)	Median simulated temperature (°C) (min;max)	Median simulated SAR (W/kg) (min; max)	Median applied total power (W) (min; max)
Cervix/vagina	Vagina	40.3 (37.5;41.8)	40.7 (39.2;43.2)	37.8 (24.9;72.4)	600 (300;850)
23 patients/37 events	Bladder	40.9 (39.1;42.6)	40.1 (38.5;41.0)	35.4 (17.2;50.8)
	Rectum	40.2 (38.9;41.2)	39.7 (38.6;41.4)	28.5 (5.9;59.4)
Bladder	Vagina	40.6 (38.5;41.6)	39.9 (39.2;40.3)	35.0 (24.9;37.5)	675 (500;900)
14 patients/29 events	Bladder	40.6 (37.8;41.8)	40.6 (39.3;42.7)	30.7 (21.1;50.9)
	Rectum	40.0 (38.4;42.0)	39.0 (38.1;39.9)	24.1 (0.1;41.5)
Vulva	Vagina	40.2 (−)	42.0 (−)	59.7 (−)	700 (−)
1 patient/1 event	Bladder	–	–	–
	Rectum	39.9 (−)	41.8 (−)	60.5 (−)

Figure 3. Correlation between measured changes in temperature and simulated changes in SAR after phase-amplitude steering for the vagina, bladder, and rectum, as well as for the vagina and rectum together.

Figure 4. Correlation between measured and simulated changes in temperature after phase-amplitude steering for the vagina, bladder, and rectum, as well as for the vagina and rectum together. The shaded green region indicates the region where simulated and measured differences correspond within ±0.1 °C.

Figure 5. Histograms of the deviations between simulated and measured changes in temperature after phase-amplitude steering for the vagina, bladder, and rectum, as well as for the vagina and rectum together.

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