‘Relationship between thermal dose and cell death for “rapid” ablative and “slow” hyperthermic heating’

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 CEM43) using a thermal cycler for hyperthermic (>2 minutes, 55 °C). TID was initially estimated using a constant RCEM>43°C=0.5, and subsequently using RCEM(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 CEM43 (RCEM>43°C=0.5), while 340-550 CEM43 (RCEM>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 × 105 J mole−1, frequency factor A = 3.27 ± 11 × 1091 sec−1) yielded RCEM=0.42 * e0.0041*T which better-predicted cell survival than using R CEM> 43°C=0.5. Conclusions: TID calculated using an RCEM(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 CEM43 using this revised measure.

研究目的：热等效应剂量（Thermal isoeffective dose, TID）尚未被可靠验证，无法用于预测快速热消融（如采用高于55℃温度的操作）引发的生物学效应。本研究对比了两种量化TID的方法：一种是源自热疗数据的经典方法，另一种是基于阿伦尼乌斯（Arrhenius）模型的温度校正方法，用于预测体外（in vitro）细胞在“快速”消融性热疗或“慢速”热疗暴露后的存活率。

研究方法：本研究针对两种人结肠癌细胞系（HCT116、HT29），采用MTT检测法（MTT assay）获取细胞存活能力数据。使用热循环仪对细胞进行热疗处理，热暴露时长大于2分钟、温度为55℃，设置的热等效应剂量范围为120~720 CEM43。TID的计算最初采用恒定RCEM>43℃=0.5，后续则采用基于温度依赖性细胞存活（损伤速率）的阿伦尼乌斯分析得到的RCEM(T)。

研究结果：当采用RCEM>43℃=0.5计算TID，且TID为240 CEM43时，“慢速”与“快速”热暴露后的两种细胞系均出现细胞存活，并在处理后10天出现显著增殖；当采用“快速”热暴露方式递送340~550 CEM43（RCEM>43℃=0.5）时，细胞存活率为12±6%，而采用“慢速”热暴露则未检测到细胞存活。对实验数据进行阿伦尼乌斯分析后，得到活化能ΔE=5.78±0.04×10^5 J·mol^-1，频率因子A=3.27±11×10^91 s^-1，得到RCEM=0.42×e^(0.0041*T)，该模型相比RCEM>43℃=0.5能更准确地预测细胞存活率。

研究结论：采用基于阿伦尼乌斯动力学参数得到的RCEM(T)计算TID，可得到更一致、不受热疗策略影响的细胞存活率预测模型，优化了消融性热暴露的剂量学计算。采用该修正方法后，仅当TID高于305±10 CEM43时，才无法检测到细胞存活。