Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
Acta Oncol. 2012 Mar;51(3):318-24. doi: 10.3109/0284186X.2012.666358.
Interest in boosting the dose to the tumour during neo-adjuvant radiochemotherapy for rectal cancer is ever increasing, especially within the frame of adaptive radiotherapy. Rectal motion remains a potentially important obstacle to the full exploitation of this approach and needs to be carefully investigated.
The main purposes of this work were to: a) quantify rectal motion on all fractions of a treatment course; and b) assess margins for adaptive boosting in the second part of the treatment in order to benefit of tumour reduction during treatment. Ten consecutive patients treated with image-guided tomotherapy (41.4 Gy, 18 fractions) were selected. The cranial half of the rectum (subject to motion) was contoured by a single observer on daily MVCTs. The variations of rectal volume and of the envelope of rectum positions were investigated (169 MVCTs). The impact of applying different margins to the rectum in including all its possible positions was also investigated when considering the planning kVCT, the first fraction MVCT, the half-treatment MVCT or the median rectal contours of the whole or second half of treatment as reference volumes.
Rectal volume reduced during treatment in all patients, with a significant time-trend in 6/10 patients. The median values of the envelope volumes were 129 cm(3) and 87 cm(3) in the first and second half of the treatment, respectively. On average, 95% of the rectal envelope was included by an isotropic expansion of 12 mm and 5 mm of the median contours when considering the whole or the second half of the treatment, respectively.
A significant reduction of rectal volume was found in the second part of the treatment where rectal mobility was limited. As a consequence, relatively small margins may be used around the residual tumour volume when adaptive boost is delivered in the second half of the treatment.
在新辅助放化疗治疗直肠癌过程中，人们越来越感兴趣的是提高肿瘤剂量，特别是在自适应放疗的框架内。直肠运动仍然是充分利用这种方法的一个潜在重要障碍，需要仔细研究。
本研究的主要目的是：a）量化治疗过程中所有分次的直肠运动；b）评估第二部分治疗中自适应提升的边界，以受益于治疗过程中的肿瘤缩小。选择 10 例连续接受图像引导调强放疗（41.4 Gy，18 分次）的患者。直肠的颅侧半（受运动影响）由一名观察者在每日 MVCT 上勾画。研究了直肠体积和直肠位置包络的变化（169 个 MVCT）。当考虑计划 kVCT、第一分次 MVCT、半程 MVCT 或整个或后半程的中位直肠轮廓作为参考体积时，还研究了将不同边界应用于直肠以包括其所有可能位置的影响。
所有患者的直肠体积在治疗过程中均减少，6/10 例患者有显著的时间趋势。治疗前半程和后半程的直肠包络体积中位数分别为 129cm(3)和 87cm(3)。平均而言，当考虑整个或后半程治疗时，直肠包络的 95%可以通过对中位轮廓的 12mm 和 5mm 各向同性扩张来包括。
在第二部分治疗中，直肠体积明显减少，此时直肠移动性受限。因此，在第二部分治疗中给予自适应增敏时，残留肿瘤体积周围可以使用相对较小的边界。
