Istituto di Fisica, Università Cattolica del S. Cuore, Rome, Italy.
J Appl Clin Med Phys. 2011 Nov 15;12(4):3538. doi: 10.1120/jacmp.v12i4.3538.
A practical and accurate generalized procedure to reconstruct the isocenter dose D(iso) for 3D conformal radiotherapy (3DCRT) has been developed for X-ray open beams supplied by linacs of different manufacturers and equipped with aSi electronic portal imaging devices (aSi EPIDs). This paper reports an extension of the method, to be applied at the wedged X-ray beams characterized by the wedge attenuation factor W(AF). Using water-equivalent solid phantoms (SPs) of different thicknesses, w, and photon square fields of sizes, L, the generalized midplane doses D(0)(W(AF), w/2,L) and generalized transit signals s(t)(0)(W(AF),w,L) by 38 beams of six different linacs were determined. The generalized data were fitted by surface equations and used together with the information of the ‘record & verify’ network of the centers. In this manner, for every beam, the D(iso) reconstruction was obtained in about 25 seconds after the treatment. To test the in vivo dosimetric procedure, six pelvic treatments that used conformed wedged beams were carried out with three linacs of different manufacturers. For every beam, the comparison between the reconstructed D(iso) and the D(iso,TPS) computed by the TPS, resulted in an acceptable tolerance level of ±5%, estimated for this kind of treatment. Generally the in vivo dosimetry methods that use EPIDs require: (i) a special effort for the dosimetric commissioning with SPs of different thicknesses, and (ii) extra time for the analysis of the EPID signals. The proposed procedure simplifies the commissioning step and supplies for Varian, Elekta, and Siemens linacs equipped with the aSi EPIDs a quasi-real time in vivo dosimetry for open and wedged 3DCRT fields.
已经开发出一种实用且精确的方法，可用于重建不同制造商生产的配备有 aSi 电子射野影像装置（aSi EPID）的医用直线加速器产生的开放束和楔形束的三维适形放疗（3DCRT）等中心剂量 D（iso）。本文报告了该方法的扩展，将应用于楔形 X 射线束，其特征为楔形衰减因子 W（AF）。使用不同厚度 w 的水等效固体体模（SP）和大小为 L 的光子正方形射野，确定了 38 束来自六台不同医用直线加速器的广义中平面剂量 D（0）（W（AF），w/2，L）和广义传输信号 s（t）（0）（W（AF），w，L）。广义数据通过曲面方程进行拟合，并与中心的“记录与验证”网络信息一起使用。通过这种方式，对于每束射线，在治疗后大约 25 秒内即可重建 D（iso）。为了测试体内剂量学方法，使用三台不同制造商的医用直线加速器进行了六个骨盆楔形束适形放疗。对于每束射线，重建的 D（iso）与治疗计划系统（TPS）计算的 D（iso，TPS）之间的比较结果，在这种治疗中估计具有可接受的±5%容差水平。通常，使用 EPID 的体内剂量学方法需要：（i）使用不同厚度的 SP 进行剂量学调试的特殊工作，（ii）对 EPID 信号进行分析的额外时间。所提出的方法简化了调试步骤，并为配备有 aSi EPID 的瓦里安（Varian）、医科达（Elekta）和西门子（Siemens）医用直线加速器提供了用于开放和楔形 3DCRT 射野的准实时体内剂量学。
