wIRA-heating of piglet skin and subcutis in vivo: proof of accordance with ESHO criteria for superficial hyperthermia

Abstract

Purpose

The quality assurance guidelines of the European Society for Hyperthermic Oncology (ESHO) specify the requirements for appropriate superficial heating using phantoms. In this current piglet study, we have examined these requirements under in vivo conditions.

Materials and Methods

The evaluation is based on simultaneous, invasive temperature measurements at 8 different depths between 2 and 20 mm in the thigh of anesthetized piglets during irradiation with water-filtered infrared radiation (wIRA). Temperature probes were equally distributed in an area of 10 cm diameter of homogeneously irradiated skin. Piglets were irradiated to 126.5 mW cm⁻² in the spectral range of IR-A.

Results

Heating rates and specific absorption rates were in full accordance with the ESHO standards. Due to early onset of thermoregulation, the desired temperature rise of 6 K at a depth of 5 mm was achieved after about 10 min of exposure, i.e. 4 min later than required for phantoms. After reaching thermal steady state, on average T₉₀ ≥ 40 °C occurred in tissue depths up to 20 mm, T₅₀ ≥ 41 °C up to 16 mm, and a mean CEM₄₃T₉₀ ≈ 1 min was calculated for depths up to 8 mm.

Conclusions

Piglet data are comparable with preliminary literature data assessed in vivo in the abdominal wall and in recurrent breast cancer of humans. The potential of wIRA-HT for adequate treatment of superficial tissues/cancers in the clinical setting thus is confirmed. To ensure therapeutically needed doses of wIRA-HT, irradiation times should be extended.

Keywords:

• Water-filtered infrared-A (wIRA)
• superficial hyperthermia
• ESHO guidelines
• heating rate
• specific absorption rate
• temperature rise

Disclosure statement

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

Ethics statement

Ethical approval for the experiments was obtained from Veterinäramt Kanton Zürich (Ref.: ZH180/15). Date of approval: February 9, 2016.

Additional information

Funding

This study was supported by the Dr. med. h.c. Erwin Braun Foundation, Basel, Switzerland (H.P., W.M.). Peter Vaupel is a long-standing board member ad honorem of the Dr. med. h.c. Erwin Braun Foundation.