'Relationship between thermal dose and cell death for "rapid" ablative and "slow" hyperthermic heating'.

Abstract

Aim Thermal isoeffective dose (TID) has not been convincingly validated for application to predict biological effects from rapid thermal ablation (e.g., using >55 °C). This study compares the classical method of quantifying TID (derived from hyperthermia data) with a temperature-adjusted method based on the Arrhenius model for predicting cell survival in vitro, after either 'rapid' ablative or 'slow' hyperthermic exposures.Methods MTT assay viability data was obtained from two human colon cancer cell lines, (HCT116, HT29), subjected to a range of TIDs (120-720 CEM 43 ) using a thermal cycler for hyperthermic (>2 minutes, <50 °C) treatments, or a novel pre-heated water bath based technique for ablative exposures (<10 seconds, >55 °C). TID was initially estimated using a constant R CEM>43 ° C =0.5, and subsequently using R CEM (T), derived from temperature dependent cell survival (injury rate) Arrhenius analysis.Results 'Slow' and 'rapid' exposures resulted in cell survival and significant regrowth (both cell lines) 10 days post-treatment for 240 CEM 43 (R CEM>43 ° C =0.5), while 340-550 CEM 43 (R CEM>43 ° C =0.5) delivered using 'rapid' exposures showed 12 ± 6% viability and 'slow' exposures resulted in undetectable viability. Arrhenius analysis of experimental data (activation energy ΔE = 5.78 ± 0.04 × 10 5 J mole -1 , frequency factor A = 3.27 ± 11 × 10 91 sec -1 ) yielded R CEM =0.42 * e 0.0041*T which better-predicted cell survival than using R CEM> 43 ° C =0.5.Conclusions TID calculated using an R CEM (T) informed by Arrhenius kinetic parameters provided a more consistent, heating strategy independent, predictor of cell viability, improving dosimetry of ablative thermal exposures. Cell viability was only undetectable above 305 ± 10 CEM 43 using this revised measure.