Physical and Photobiological Basics of wIRA-Hyperthermia

Excerpt

Information regarding physical and photobiological basics of wIRA-HT has been derived under in vivo conditions in piglets and human tissues. Since wIRA fits into the optical window of tissues, direct conversion of absorbed radiation into heat (T >39 °C) has been proven up to tissue depths of 26 mm. Tissue heating cannot sufficiently be characterized by the specification of the radiant exposure (dose) due to its dependence on the thermal impact of irradiance and exposure time and on heat dissipation and metabolic heat production. If irradiations of identical doses are used, resulting tissue hyperthermia levels are the higher, the shorter the exposure time and the higher the irradiance. To comply with the ESHO criteria, incident wIRA irradiances should exceed ≈ 110 mWcm⁻² (IR-A). At higher irradiances, steady-state temperatures (SST) ≥ 39 °C have been observed to tissue depths >20 mm in piglets and up to 26 mm in humans. SST values ≥40 °C have been measured up to tissue depths >20 mm (piglets) and up to 16 mm (humans), and SSTs ≥41 °C up to 16 mm (piglets) and up to 8 mm (humans). Post-heating temperature decay times limit optimal intervals between hyperthermia (HT) and subsequent radiotherapy (RT) sessions to periods ≤5 min.