Radiotherapy Physics Unit, Bristol Haematology and Oncology Centre, University Hospitals Bristol NHS Foundation Trust, UK.
Br J Radiol. 2012 Dec;85(1020):e1249-55. doi: 10.1259/bjr/30377872.
The aim of this study was to assess the impact of dose escalation on the proportion of patients requiring MR image-guided optimisation rather than standard Manchester-based CT-guided planning, and the level of escalation achievable.
30 patients with cervical cancer treated with external beam radiotherapy and image-guided brachytherapy (IGBT) had MR images acquired at the first fraction of IGBT. Gross tumour volume and high-risk clinical target volume (HR CTV) were contoured and treatment plans retrospectively produced for a range of total 2-Gy equivalent (EQD2) prescription doses from 66 Gy(α/β=10) to 90 Gy(α/β=10) (HR CTV D90). Standard Manchester system-style plans were produced, prescribed to point A and then optimised where necessary with the aim of delivering at least the prescription dose to the HR CTV D90 while respecting organ-at-risk (OAR) tolerances.
Increasing the total EQD2 from 66 Gy(α/β=10) to 90 Gy(α/β=10) increased the number of plans requiring optimisation from 13.3% to 90%. After optimisation, the number of plans achieving the prescription dose ranged from 93.3% (66 Gy(α/β=10)) to 63.3% (90 Gy(α/β=10)) with the mean ± standard deviation for HR CTV D90 EQD2 from 78.4 ± 12.4 Gy(α/β=10) (66 Gy(α/β=10)) to 94.1 ± 19.9 Gy(α/β=10) (90 Gy(α/β=10)).
As doses are escalated, the need for non-standard optimised planning increases, while benefits in terms of increased target doses actually achieved diminish. The maximum achievable target dose is ultimately limited by proximity of OARs.
This work represents a guide for other centres in determining the highest practicable prescription doses while considering patient throughput and maintaining acceptable OAR doses.
本研究旨在评估剂量递增对需要磁共振图像引导优化而不是标准曼彻斯特 CT 引导计划的患者比例的影响，以及可实现的递增水平。
30 例宫颈癌患者接受外照射放疗和图像引导近距离放疗（IGBT），在 IGBT 的第一部分采集 MR 图像。勾画大体肿瘤体积和高危临床靶区（HR CTV），并为总 2-Gy 等效（EQD2）处方剂量范围从 66 Gy（α/β=10）到 90 Gy（α/β=10）（HR CTV D90）生成治疗计划。生成标准曼彻斯特系统风格的计划，规定点 A，然后在必要时进行优化，目的是在尊重危及器官（OAR）耐受的情况下，将至少处方剂量输送到 HR CTV D90。
将总 EQD2 从 66 Gy（α/β=10）增加到 90 Gy（α/β=10），需要优化的计划数量从 13.3%增加到 90%。优化后，达到处方剂量的计划数量范围从 93.3%（66 Gy（α/β=10））到 63.3%（90 Gy（α/β=10）），HR CTV D90 EQD2 的平均值±标准差从 78.4±12.4 Gy（α/β=10）（66 Gy（α/β=10））增加到 94.1±19.9 Gy（α/β=10）（90 Gy（α/β=10））。
随着剂量的增加，对非标准优化计划的需求增加，而实际实现的靶区剂量增加的益处减少。最大可实现靶区剂量最终受到 OAR 接近度的限制。
这项工作为其他中心确定最高可行的处方剂量提供了指导，同时考虑了患者吞吐量和保持可接受的 OAR 剂量。
