Daşu Alexandru, Toma-Daşu Iuliana
Department of Radiation Physics, Norrland University Hospital, Umeå, Sweden.
Int J Radiat Oncol Biol Phys. 2008 Mar 1;70(3):867-74. doi: 10.1016/j.ijrobp.2007.07.2358. Epub 2007 Sep 24.
To study the clinically relevant relative biologic effectiveness (RBE) of fractionated treatments with high linear energy transfer (LET) radiation and to identify the important factors that might influence the transfer of tolerance and curative levels from low LET radiation. These are important questions in the light of the growing interest for the therapeutic use of radiation with higher LET than electrons or photons.
The RBE of various fractionated schedules was analyzed with theoretical models for radiation effect, and the resulting predictions were compared with the published clinical and experimental data regarding fractionated irradiation with high LET radiation.
The clinically relevant RBE increased for greater doses per fraction, in contrast to the predictions from single-dose experiments. Furthermore, the RBE for late-reacting tissues appeared to modify more quickly than that for early-reacting tissues. These aspects have quite important clinical implications, because the increased biologic effectiveness reported for this type of radiation would otherwise support the use of hypofractionation. Thus, the differential between acute and late-reacting tissues could put the late-reacting normal tissues at more risk from high LET irradiation; however, at the same time, it could increase the therapeutic window for slow-growing tumors.
The modification of the RBE with the dose per fraction must be carefully taken into consideration when devising fractionated treatments with high LET radiation. Neglecting to do so might result in an avalanche of complications that could obscure the potential advantages of the therapeutic use of this type of radiation.
研究高传能线密度（LET）辐射分次治疗的临床相关相对生物效应（RBE），并确定可能影响低LET辐射耐受性和治愈水平转移的重要因素。鉴于人们对使用比电子或光子LET更高的辐射进行治疗的兴趣日益浓厚，这些都是重要问题。
使用辐射效应理论模型分析各种分次照射方案的RBE，并将所得预测结果与已发表的关于高LET辐射分次照射的临床和实验数据进行比较。
与单剂量实验的预测结果相反，临床相关RBE随每次分割剂量增加而增加。此外，晚反应组织的RBE似乎比早反应组织变化更快。这些方面具有相当重要的临床意义，因为否则报道的这类辐射增加的生物学效应将支持大分割放疗的应用。因此，早反应组织与晚反应组织之间的差异可能使晚反应正常组织在高LET照射下面临更大风险；然而，与此同时，它可能增加生长缓慢肿瘤的治疗窗。
在设计高LET辐射分次治疗方案时，必须仔细考虑RBE随每次分割剂量的变化。忽视这一点可能导致并发症大量出现，从而掩盖这类辐射治疗应用的潜在优势。
