Armoogum Kris, Evans Simon, Morgan David
Department of Radiotherapy Physics, Royal Derby Hospital, Derby Teaching Hospitals NHS Foundation Trust, Uttoxeter Road, Derby.
Breast Services, Sherwood Forest Hospitals NHS Foundation Trust, Sutton-in-Ashfield, Nottingham, United Kingdom.
J Contemp Brachytherapy. 2016 Aug;8(4):313-8. doi: 10.5114/jcb.2016.61758. Epub 2016 Aug 16.
We present a framework, in which we compare a conventional standard dose of 50 Gy in 25 fractions with accelerated partial breast irradiation (APBI) using electronic brachytherapy (eBT). We discuss how radiobiological modelling enables us to establish a framework, within which we can compare external beam radiotherapy (EBRT). This leads to a determination of the shell of isoeffect in breast tissue, at which very low kV eBT can be considered to be clinically equivalent to standard EBRT.
To estimate relative biological effectiveness (RBE) values as a function of dose and irradiation time, we used a modified linear quadratic (LQ) approach, taking into account the ability of this new device, to deliver 20 Gy at the surface of a 40 mm diameter rigid, hollow spherical applicator in less than 2 minutes. In this study, we considered the radiobiological effectiveness of the Papillon +™ X-ray brachytherapy device operating at 30 kV, 0.3 mA producing dose rates in excess of 14 Gy/min.
Calculated clinical RBEs ranged from 1.154 at the surface of a 40 mm diameter applicator to 1.100 at 35 mm from the applicator surface for the Papillon+ device. The absolute physical dose D (abs) 30 kV ranged from 20.00 Gy at the applicator surface to 1.20 at 35 mm distant. The product of the isoeffective single dose of (60)Co reference radiation - (RBE)(60)Co, and the RBE corrected standard 2 Gy equivalent dose fractions (EQD2) doses, EQD2(30 kV) * (RBE)(60)Co ranged from 98.62 Gy at the applicator surface to 1.13 at 35 mm. The 'shell of isoeffect', the value on the X-axis where the EQD2(30 kV) * (RBE)(60)Co line crosses the 50 Gy mark on the Y-axis, was found to be approximately 3.5 mm beyond the applicator surface.
The 'shell of isoeffect' can serve as a useful metric with which to compare the radiobiological effectiveness of low kV eBT with various regimes of conventional EBRT.
我们提出了一个框架，在该框架中，我们将25次分割的传统标准剂量50 Gy与使用电子近距离放射治疗（eBT）的加速部分乳腺照射（APBI）进行比较。我们讨论了放射生物学建模如何使我们能够建立一个框架，在这个框架内我们可以比较外照射放疗（EBRT）。这导致确定乳腺组织中的等效应壳层，在该壳层处，非常低千伏的eBT可被认为在临床上等同于标准EBRT。
为了估计作为剂量和照射时间函数的相对生物效应（RBE）值，我们使用了一种改进的线性二次（LQ）方法，考虑到这种新设备能够在不到2分钟的时间内在直径40 mm的刚性空心球形施源器表面给予20 Gy的剂量。在本研究中，我们考虑了工作在30 kV、0.3 mA且剂量率超过14 Gy/min的Papillon +™ X射线近距离放射治疗设备的放射生物学有效性。
对于Papillon +设备，计算得出的临床RBE范围从直径40 mm施源器表面的1.154到距施源器表面35 mm处的1.100。30 kV时的绝对物理剂量D（abs）范围从施源器表面的20.00 Gy到35 mm远处的1.20。等效单次剂量的（60）Co参考辐射 - （RBE）（60）Co与经RBE校正的标准2 Gy等效剂量分数（EQD2）剂量的乘积，EQD2（30 kV）（RBE）（60）Co范围从施源器表面的98.62 Gy到35 mm处的1.13。“等效应壳层”，即EQD2（30 kV）（RBE）（60）Co线与Y轴上50 Gy标记相交处X轴上的值，被发现约在施源器表面之外3.5 mm处。
“等效应壳层”可作为一个有用的指标，用于比较低千伏eBT与各种传统EBRT方案的放射生物学有效性。
