CRUK-MRC Oxford Centre, Gray Laboratory, Department of Oncology, University of Oxford, Old Road Research Campus Research Building, Roosevelt Drive, Oxford OX3 7DQ, United Kingdom; Green Templeton College, University of Oxford, 43 Woodstock Road, Oxford, OX2 6HG, United Kingdom.
Green Templeton College, University of Oxford, 43 Woodstock Road, Oxford, OX2 6HG, United Kingdom.
Phys Med. 2019 Aug;64:304-310. doi: 10.1016/j.ejmp.2019.04.005. Epub 2019 Apr 13.
Re-treatment, using megavoltage photon radiotherapy, can benefit carefully selected patients with new or recurrent tumours. Such re-treatments may involve the further exposure of tissues such as the brain or spinal cord. A time-dependent model has been developed, which incorporates data from all published radiobiological experiments concerned with the in vivo re-irradiation of the spinal cord using photons. It allows an estimation of the increasing recovery in tissue tolerance with elapsed time after the initial treatment course. In accordance with the experimental evidence, the recovery rate depends on the biological effective dose (BED) of the initial treatment. Various degrees of conservatism have been introduced in the model to allow for potential changes in CNS tissue tolerance due to patient age, chemotherapy, surgery etc. An estimation of the re-treatment dose-fractionation schedule is made easier by the use of a downloadable Graphical User Interface (GUI). Worked examples of its use are given forconventional photon (X-ray) based treatments, and also for protons, where relative biological effectiveness (RBE) considerations must be respected within the BED estimates. The model provides boundary conditions for clinical practice. The responsible clinician can choose to usemore 'forgiving' BED values and from this to calculate the re-irradiation dose-fractionation schedule. For protons, greater care is required sincethe inter-relationship between linear energy transfer (LET) and RBE can lead to significant over-dosage relative to accepted CNS tolerance doses, especially with the use of scanned proton beams. LET and RBE factors are important in order to deliver safe and effective re-treatment doses.
重新治疗，使用兆伏级光子放射治疗，可以使精心挑选的患有新的或复发肿瘤的患者受益。这种再治疗可能涉及进一步暴露于脑组织或脊髓等组织。已经开发了一种时变模型，该模型结合了所有关于使用光子对脊髓进行体内再照射的已发表放射生物学实验的数据。它允许估计在初始治疗过程后经过一段时间，组织耐受力的逐渐恢复。根据实验证据，恢复速度取决于初始治疗的生物有效剂量（BED）。在模型中引入了不同程度的保守性，以考虑由于患者年龄、化疗、手术等因素导致中枢神经系统组织耐受力的潜在变化。通过使用可下载的图形用户界面（GUI），更容易估算再治疗剂量分割方案。给出了使用该 GUI 的常规光子（X 射线）治疗以及质子治疗的示例，在质子治疗中，必须在 BED 估算中考虑相对生物有效性（RBE）因素。该模型为临床实践提供了边界条件。负责的临床医生可以选择使用更“宽容”的 BED 值，并据此计算再照射剂量分割方案。对于质子治疗，需要更加小心，因为线性能量传递（LET）和 RBE 之间的相互关系可能导致相对于可接受的中枢神经系统耐受剂量的显著超剂量，特别是在使用扫描质子束时。LET 和 RBE 因素对于提供安全有效的再治疗剂量很重要。
