Clinical wIRA-hyperthermia: heating properties and effectiveness in lower trunk regions and its accordance with ESHO quality criteria for superficial hyperthermia

Abstract

Purpose

The heating characteristics of water-filtered infrared-A (wIRA) radiation were investigated in vivo in two body regions of healthy humans according to the quality standards of the European Society for Hyperthermic Oncology (ESHO) using an irradiance (infrared-A) of 146 W m⁻² as recommended for clinical superficial hyperthermia (HT).

Methods

wIRA was applied to the abdominal wall and lumbar region for 60 min. Skin surface temperature was limited to ≤43 °C. Tissue temperatures were measured invasively at 1-min intervals before, during and after wIRA exposure using five fiber-optical probes at depths of 1–20 mm.

Results

Significant differences between body regions occurred during the heating-up phase at depths of 5–15 mm. Thermal steady states were reached at depths ≤5 mm after exposures of 5–6 min, and ≤20 mm after 20 min. On average, the minimum requirements of ESHO were exceeded in both regions by the following factors: ≈3 for the heating rate, ≈2 for the specific absorption rate and ≈1.4 for the temperature rise. Tissue depths with T₉₀ ≥ 40 °C and T₅₀ > 41 °C were ≤10 mm, and ≤20 mm for T_max ≤ 43 °C. The temperature decay time after termination of irradiation was 1–5 min. Corresponding temperatures were ≤42.2 °C for CEM₄₃ and ≤41.8 °C for CEM₄₃T₉₀, i.e., they are inadequate for direct thermal cell killing.

Conclusions

Thermography-controlled wIRA-HT complies with the ESHO criteria for superficial HT as a radiosensitizer and avoids the risk of thermal skin toxicity.

Keywords:

• Water-filtered infrared-A (wIRA) irradiation
• superficial hyperthermia
• mild hyperthermia
• tissue thermometry
• skin thermography
• ESHO guidelines

Acknowledgments

The authors greatly appreciate Michael R. Saalmann’s valuable support during the experimental procedures and data acquisition and Dr. Mark Gainey, Medical Physicist, Department of Radiation Oncology, University Medical Center, University of Freiburg/Breisgau, Germany for linguistic support.

Ethical approval

This study was found to be ethically sound by the local ethics authority (EK-Freiburg 21-1158).

Consent form

After having received an explanation of the study, all volunteers signed an informed consent.

Disclosure statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be constructed as a potential conflict of interest.

Data availability statement

The data sets used and analyzed during this study are available from the corresponding author on reasonable request.

Additional information

Funding

This study was supported by Dr. med. h. c. Erwin Braun Foundation, Basel, Switzerland.