Van Dam J, Rijnders A, Vanuytsel L, Zhang H Z
Department of Radiotherapy, University Hospital St. Rafaël, Leuven, Belgium.
Radiother Oncol. 1988 Nov;13(3):193-201. doi: 10.1016/0167-8140(88)90056-4.
Total body irradiation (TBI) sometimes requires the set-up of the patient very close to the wall of the treatment room in order to obtain sufficiently large irradiation fields. Under these conditions, backscattered electrons can become clinically important. In the present study, an attempt was made to quantify the dose contribution to the patient from these electrons. Measurements were performed both in experimental conditions and on patients during their TBI treatment. It is concluded that, with the patient close to the wall, backscattered electrons constitute a significant (up to 20% of the dose obtained under electronic equilibrium at the exit port of the beam) radiation dose which can (under certain conditions) influence measurements of exist dose leading to an overestimation of the midline dose and contribute a superficial irradiation of the patient without therapeutic benefit. This problem can be solved by interposing a 2 cm thick low-Z absorber between wall and patient.
全身照射（TBI）有时需要将患者安置得非常靠近治疗室墙壁，以便获得足够大的照射野。在这些条件下，反向散射电子在临床上可能变得很重要。在本研究中，尝试对这些电子对患者的剂量贡献进行量化。在实验条件下以及患者接受TBI治疗期间均进行了测量。得出的结论是，当患者靠近墙壁时，反向散射电子构成了显著的辐射剂量（高达在束流出口处电子平衡条件下所获剂量的20%），这在某些情况下会影响出射剂量的测量，导致中线剂量被高估，并且对患者进行了无治疗益处的浅表照射。通过在墙壁与患者之间插入一块2厘米厚的低原子序数吸收体，可以解决这个问题。
