Raaphorst G P, Ng C E, Shahine B
Medical Physics Department, Ottawa Regional Cancer Centre, Ontario, Canada.
Int J Radiat Oncol Biol Phys. 1999 Apr 1;44(1):185-8. doi: 10.1016/s0360-3016(98)00565-3.
Long duration mild hyperthermia has been shown to be an effective radiosensitizer when given concurrently with low dose rate irradiation. Pulsed simulated low dose rate (PSLDR) is now being used clinically, and we have set out to determine whether concurrent mild hyperthermia can be an effective radiosensitizer for the PSLDR protocol.
Human glioma cells (U-87MG) were grown to plateau phase and treated in plateau phase in order to minimize cell cycle redistribution during protracted treatments. Low dose rate (LDR) irradiation and 41 degrees C hyperthermia were delivered by having a radium irradiator inside a temperature-controlled incubator. PSLDR was given using a 150 kVp X-ray unit and maintaining the cells at 41 degrees C between irradiations. The duration of irradiation and concurrent heating depended on total dose and extended up to 48 h.
When 41 degrees C hyperthermia was given currently with LDR or PSLDR, the thermal enhancement ratios (TER) were about the same if the average dose rate for PSLDR was the same as for LDR. At higher average dose rates for PSLDR the TERs became less.
Our data show that concurrent mild hyperthermia can be an effective sensitizer for PSLDR. This sensitization can be as effective as for LDR if the same average dose rate is used and the TER increases with decreasing dose rate. Thus mild hyperthermia combined with PSLDR may be an effective clinical protocol.
长时间轻度热疗已被证明与低剂量率照射同时进行时是一种有效的放射增敏剂。脉冲模拟低剂量率（PSLDR）目前正在临床中使用，我们着手确定同时进行的轻度热疗是否可以成为PSLDR方案的有效放射增敏剂。
将人胶质瘤细胞（U-87MG）培养至平台期，并在平台期进行处理，以尽量减少长时间治疗期间的细胞周期重新分布。通过在温度控制的培养箱内放置镭辐射器来进行低剂量率（LDR）照射和41℃热疗。使用150 kVp X射线装置给予PSLDR，并在两次照射之间将细胞维持在41℃。照射和同时加热的持续时间取决于总剂量，最长可达48小时。
当41℃热疗与LDR或PSLDR同时进行时，如果PSLDR的平均剂量率与LDR相同，则热增强比（TER）大致相同。对于PSLDR，在较高的平均剂量率下，TER会降低。
我们的数据表明，同时进行的轻度热疗可以成为PSLDR的有效增敏剂。如果使用相同的平均剂量率，这种增敏作用与LDR一样有效，并且TER随剂量率降低而增加。因此，轻度热疗联合PSLDR可能是一种有效的临床方案。
