Department of Medical Physics, The Norwegian Radium Hospital, Oslo University Hospital, Nydalen, Oslo, Norway.
Acta Oncol. 2010 Oct;49(7):1116-23. doi: 10.3109/0284186X.2010.498832.
High resolution beam delivery may be required for optimal biology-guided adaptive therapy. In this work, we have studied the influence of multi leaf collimator (MLC) leaf widths on the treatment outcome following adapted IMRT of a hypoxic tumour.
Dynamic contrast enhanced MR images of a dog with a spontaneous tumour in the nasal region were used to create a tentative hypoxia map following a previously published procedure. The hypoxia map was used as a basis for generating compartmental gross tumour volumes, which were utilised as planning structures in biologically adapted IMRT. Three different MLCs were employed in inverse treatment planning, with leaf widths of 2.5 mm, 5 mm and 10 mm. The number of treatment beams and the degree of step-and-shoot beam modulation were varied. By optimising the tumour control probability (TCP) function, optimal compartmental doses were derived and used as target doses in the inverse planning. Resulting IMRT dose distributions and dose volume histograms (DVHs) were exported and analysed, giving estimates of TCP and compartmental equivalent uniform doses (EUDs). The impact of patient setup accuracy was simulated.
The MLC with the smallest leaf width (2.5 mm) consistently gave the highest TCPs and compartmental EUDs, assuming no setup error. The difference between this MLC and the 5 mm MLC was rather small, while the MLC with 10 mm leaf width gave considerably lower TCPs. When including random and systematic setup errors, errors larger than 5 mm gave only small differences between the MLC types. For setup errors larger than 7 mm no differences were found between non-uniform and uniform dose distributions.
Biologically adapted radiotherapy may require MLCs with leaf widths smaller than 10 mm. However, for a high probability of cure it is crucial that accurate patient setup is ensured.
为实现最佳生物学引导自适应治疗，可能需要高分辨率射束传输。在这项工作中，我们研究了多叶准直器（MLC）叶片宽度对缺氧肿瘤自适应调强放疗（IMRT）后治疗效果的影响。
使用一只狗的鼻腔区域自发肿瘤的动态对比增强磁共振图像，按照之前发表的方法创建一个暂定的缺氧图。该缺氧图用作生成分割大体肿瘤体积的基础，这些体积用作生物学自适应调强 IMRT 的计划结构。在逆治疗计划中使用了三种不同的 MLC，叶片宽度分别为 2.5mm、5mm 和 10mm。治疗束的数量和步进射击光束调制的程度有所不同。通过优化肿瘤控制概率（TCP）函数，得出了最优的分割剂量，并将其用作逆规划中的目标剂量。导出和分析了由此产生的调强放疗剂量分布和剂量体积直方图（DVH），给出了 TCP 和分割等效均匀剂量（EUD）的估计值。模拟了患者设置准确性的影响。
假设没有设置误差，叶片宽度最小的 MLC（2.5mm）始终给出最高的 TCP 和分割 EUD。与 5mm MLC 相比，这种 MLC 的差异相当小，而叶片宽度为 10mm 的 MLC 则给出了较低的 TCP。当包括随机和系统设置误差时，大于 5mm 的误差在 MLC 类型之间只产生很小的差异。对于大于 7mm 的设置误差，在非均匀和均匀剂量分布之间没有发现差异。
生物学自适应放疗可能需要叶片宽度小于 10mm 的 MLC。然而，为了获得高治愈率，确保患者的精确设置是至关重要的。
