Hyperthermia treatment planning for cervical cancer patients based on electrical conductivity tissue properties acquiredin vivowith EPT at 3 T MRI

Abstract

Introduction The reliability of hyperthermia treatment planning (HTP) is strongly dependent on the accuracy of the electric properties of each tissue. The values currently used are mostly based on ex vivo measurements. In this study, in vivo conductivity of human muscle, bladder content and cervical tumours, acquired with magnetic resonance-based electric properties tomography (MR-EPT), are exploited to investigate the effect on HTP for cervical cancer patients. Methods Temperature-based optimisation of five different patients was performed using literature-based conductivity values yielding certain antenna settings, which are then used to compute the temperature distribution of the patient models with EPT-based conductivity values. Furthermore, the effects of altered bladder and muscle conductivity were studied separately. Finally, the temperature-based optimisation was performed with patient models based on EPT conductivity values. Results The tumour temperatures for all EPT-based dielectric patient models were lower compared to the optimal tumour temperatures based on literature values. The largest deviation was observed for patient 1 with ΔT90 = -1.37 °C. A negative impact was also observed when the treatment was optimised based on the EPT values. For four patients ΔT90 was less than 0.6 °C; for one patient it was 1.5 °C. Conclusions Electric conductivity values acquired by EPT are higher than commonly used from literature. This difference has a substantial impact on cervical tumour temperatures achieved during hyperthermia. A higher conductivity in the bladder and in the muscle tissue surrounding the tumour leads to higher power dissipation in the bladder and muscle, and therefore to lower tumour temperatures.

A review on hyperthermia via nanoparticle-mediated therapy

“…al. [24] presented the in vivo conductivity of human muscle, bladder content and cervical tumours, acquired with magnetic resonance-based electric properties tomography (MR-EPT). The temperature-based optimisation was performed with patient models based on conductivity values.…”

“…A correlation between erysipelas (a streptococcal skin infection) and tumour regression had been observed for over a century before William Coley in 1891 [1] first documented evidence of a relationship between infection and cancer regression in sarcoma patients. Ever-expanding research on the hyperthermic treatment of cancer has been sustained over the past four decades [1][2][3][4][5][6][7][8][9][10][11][12]. In some hyperthermia treatments, the patient's blood is warmed up by an external device before it is re-transfused to the target volume (e.g.…”

Clinical validation of a novel thermophysical bladder model designed to improve the accuracy of hyperthermia treatment planning in the pelvic region

“…A major step forward was the use of more reliable input data. Recent research has shown that the dielectric properties, and in particular the electric conductivity, of urine differ noticeably from the values hitherto used in our treatment planning system; this was shown to have a significant impact on the specific absorption rate (SAR) and temperature distributions in the pelvic area [31].…”

Accuracy and precision of electrical permittivity mapping at 3T: the impact of three mapping techniques

“…Knowledge of electrical tissue properties is necessary to build patient‐specific electromagnetic (EM) models, which are fundamental for radiofrequency (RF) safety and treatment planning for therapeutic heating of malignant tissues using RF or microwave antennas . For example, patient‐specific electrical properties may be used as input for planning in locoregional hyperthermia treatment of patients with pelvic tumors (e.g., cervix) with phased arrays of 70‐130 MHz antennas .…”

“…Knowledge of electrical tissue properties is necessary to build patient‐specific electromagnetic (EM) models, which are fundamental for radiofrequency (RF) safety and treatment planning for therapeutic heating of malignant tissues using RF or microwave antennas . For example, patient‐specific electrical properties may be used as input for planning in locoregional hyperthermia treatment of patients with pelvic tumors (e.g., cervix) with phased arrays of 70‐130 MHz antennas . In this frequency range, however, electrical properties might vary (e.g., the permittivity variation is 11% in muscle and 15% in the cervix) because of their dispersive nature; thus, electrical properties should be characterized at a frequency near the frequency used for treatment in order to improve the reliability of treatment planning.…”