Radiobiological characterization of the very high dose rate and dose per pulse electron beams produced by an IORT (intra operative radiation therapy) dedicated linac
Radiobiological characterization of the very high dose rate and dose per pulse electron beams produced by an IORT (intra operative radiation therapy) dedicated linac
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IORT（术中放射治疗）专用直线加速器产生的极高剂量率和每脉冲电子束剂量的放射生物学特征
DOI：
10.21037/13782
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发表时间：
2017
影响因子：
0.9
通讯作者：
F. Martino
中科院分区：
文献类型：
--
作者：
P. Scampoli;C. Carpentieri;M. Giannelli;V. Magaddino;L. Manti;C. Moriello;M. Piliero;S. Righi;F. Martino
背景资料：术中放射治疗（IORT）是一种结合手术和放射治疗的癌症治疗方式，允许在肿瘤切除时提供大剂量的单次放射。在过去的几年中，IORT已成为临床常规中的一种广泛技术。这是可能的，由于最近开发的小型专用，因此非常灵活，电子加速器适用于外科手术环境。然而，由这些专用直线加速器产生的电子束在剂量率（输送的剂量/照射时间）、每个脉冲的剂量（每个发射的束脉冲输送的剂量）和能谱方面与由在常规放射治疗中使用的直线加速器产生的电子束不同。特别是非常高的剂量率和每脉冲剂量（即，分别是常规放射治疗的约20倍和100倍）提出了一些尚未完全研究的放射生物学问题。这项工作的目的是通过实验构建细胞存活的剂量-反应曲线来评估IORT束的相对生物学有效性（RBE）。研究方法：由于乳腺癌代表通过IORT治疗的选择性恶性肿瘤，因此在来自乳腺组织恶性腺癌的MCF-7细胞系中测定克隆形成存活率，作为不同剂量率（5、25和75戈伊/min）和每次脉冲剂量（4.2和7.4 c戈伊/脉冲）的剂量的函数。在IORT加速器Novac 7（Hitesys SpA，意大利）处进行辐照，所述IORT加速器以7 MeV的标称能量递送电子。为了比较，还用常规放射治疗加速器（ClinacR DHX，Varian）进行辐照，提供6 MeV脉冲电子束和6 MV X射线（剂量率和每脉冲剂量分别为2戈伊/min和0.1 c戈伊/脉冲）作为参考辐照。结果如下：IORT射束有效性在不同剂量率（5、25和75戈伊/min）和每次脉冲剂量（4.2和7.4 c戈伊/脉冲）下几乎相同。IORT和常规电子束之间也没有显着差异，而6 MV X射线（用于乳腺癌的常规治疗）被证明是更有效的。结论：数据显示，IORT加速器的电子束的细胞杀伤效果与常规放射治疗中使用的电子束没有显著差异。这表明，剂量率和每脉冲剂量的变化，高达75戈伊/min和7.4 c戈伊/脉冲的值，不影响束的放射生物学特性。根据我们的结果，需要新的实验数据来更好地比较IORT乳腺癌治疗（5-9 MeV电子束，单次90%等剂量水平下21戈伊）和常规乳腺癌治疗（6 MV X射线，每次2戈伊，30次）的RBE。
Background: Intra operative radiation therapy (IORT) is a cancer treatment modality combining surgery and radiation therapy that permits the delivery of a large single dose of radiation at the time of the tumour resection. During the last years, IORT has become a widespread technique in clinical routine. This was possible thanks to the recent development of small dedicated, and hence very flexible, electron accelerators suitable for a surgical operation environment. However, the electron beams produced by these dedicated linacs are different with respect to those produced by linacs used in conventional radiation therapy in terms of dose rate (dose delivered/time of irradiation), dose per pulse (dose delivered per emitted beam pulse) and energy spectrum. In particular the very high dose rate and dose per pulse (i.e., respectively about 20 and 100 times greater than those of conventional radiation therapy) pose some radiobiological questions that have not yet been fully investigated. The aim of this work was to evaluate the relative biological effectiveness (RBE) of the IORT beams through the experimental construction of dose-response curves for cell survival. Methods: Since breast cancer represents the elective malignancy for treatment by IORT, clonogenic survival was assayed in the MCF-7 cell line from breast tissue malignant adenocarcinoma as a function of dose for different dose rates (5, 25 and 75 Gy/min) and doses per pulse (4.2 and 7.4 cGy/pulse). Irradiations were performed at the IORT accelerator Novac7 (Hitesys SpA, Italy) delivering electrons at the nominal energy of 7 MeV. For comparison, irradiations were also carried out with a conventional radiotherapy accelerator (ClinacR DHX, Varian), providing a 6 MeV pulsed electron beam and 6 MV X-rays (dose rate and dose-per-pulse 2 Gy/min and 0.1 cGy/pulse respectively) as reference irradiations. Results: The IORT beam effectiveness was found almost the same with varying dose rate (5, 25 and 75 Gy/min) and dose per pulse (4.2 and 7.4 cGy/pulse). No significant difference was also found between IORT and conventional electron beams, while 6 MV X-rays (beam used in the conventional treatment of breast cancer) proved to be more effective. Conclusions: Data show that cell killing effectiveness of the electron beams from the IORT accelerator does not differ significantly from that of an electron beam used in conventional radiotherapy. This suggests that changes in the dose rate and dose per pulse, up to the values of 75 Gy/min and 7.4 cGy/pulse, do not affect the radiobiological characteristics of the beam. In the light of our results, new experimental data are needed to better compare the RBE of a IORT breast cancer treatment (5–9 MeV electron beams, 21 Gy at the 90% isodose level in single fraction) and the RBE of a conventional breast cancer treatment (6 MV X-rays, 2 Gy per fraction, 30 fractions).
影响因子：
1.6
作者：
Doria, D.;Kakolee, K. F.;Borghesi, M.
通讯作者：
Borghesi, M.