Stüben G, van der Kogel A J, van der Schueren E
Department of Experimental Radiotherapy, UZ Gasthuisberg, Leuven, Belgium.
Radiother Oncol. 1997 Feb;42(2):189-96. doi: 10.1016/s0167-8140(96)01869-5.
The aim of this study was to evaluate the biological equivalence of continuous low dose rate (LDR) irradiations to multifractionated high dose rate (HDR) regimes. The applicability of the LQ model was analysed for fraction sizes and dose rates relevant for the clinic.
Investigations were performed in mouse lip mucosa. HDR fractions were given in an overall treatment time ranging from 10 h to 3.5 days. The dose rate effect was analysed in the range of 84 to 0.76 Gy/h. For an assessment of biological equivalence in comparison to LDR, HDR irradiations have been performed in the same overall treatment time as the corresponding LDR regimes.
Recovery leads to sparing of radiation damage as the dose rate is reduced from 84 to 0.76 Gy/h (20.0 versus 45.7 Gy ED50). No significant additional sparing from 0.9 to 0.76 Gy/h could be demonstrated (44.9 versus 45.7 Gy ED50). Even 30 HDR fractions in 24 h were not sufficient to match the effect of LDR over the same time period (38.2 versus 41.1 Gy ED50). The present data give evidence for a bi-exponential repair process in mouse lip mucosa (T1/2 fast 27 min, T1/2 slow 150 min). Repair is dominated by the faster component (> 80%).
LDR is the most efficient way to deliver radiation if recovery is to be maximised and the overall time kept as short as possible. When used with realistic parameters the LQ model is capable of providing quantitative guidelines in areas of clinical interest.
本研究旨在评估连续低剂量率（LDR）照射与多分割高剂量率（HDR）方案的生物学等效性。分析了线性二次模型（LQ模型）在临床相关的分割剂量和剂量率方面的适用性。
在小鼠唇部黏膜进行研究。HDR分割照射的总治疗时间为10小时至3.5天。剂量率效应在84至0.76 Gy/h范围内进行分析。为了评估与LDR相比的生物学等效性，HDR照射与相应的LDR方案在相同的总治疗时间内进行。
随着剂量率从84 Gy/h降低至0.76 Gy/h，修复导致放射损伤减轻（ED50分别为20.0 Gy和45.7 Gy）。从0.9 Gy/h至0.76 Gy/h未显示出显著的额外减轻（ED50分别为44.9 Gy和45.7 Gy）。即使在24小时内进行30次HDR分割照射也不足以在同一时间段内与LDR的效果相匹配（ED50分别为38.2 Gy和41.1 Gy）。目前的数据证明小鼠唇部黏膜存在双指数修复过程（快速半衰期为27分钟，慢速半衰期为150分钟）。修复主要由较快的成分主导（>80%）。
如果要使修复最大化并将总时间保持尽可能短，LDR是最有效的放射治疗方式。当使用实际参数时，LQ模型能够在临床相关领域提供定量指导。
