各种在线图像引导放射治疗（IGRT）策略的比较：在线治疗计划重新优化的益处
Comparison of various online IGRT strategies: The benefits of online treatment plan re-optimization.
作者信息
Schulze Derek, Liang Jian, Yan Di, Zhang Tiezhi
机构信息
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI, USA.
出版信息
Radiother Oncol. 2009 Mar;90(3):367-76. doi: 10.1016/j.radonc.2008.08.012. Epub 2008 Oct 29.
PURPOSE
To compare the dosimetric differences of various online IGRT strategies and to predict potential benefits of online re-optimization techniques in prostate cancer radiation treatments.
MATERIALS AND METHODS
Nine prostate patients were recruited in this study. Each patient has one treatment planning CT images and 10-treatment day CT images. Five different online IGRT strategies were evaluated which include 3D conformal with bone alignment, 3D conformal re-planning via aperture changes, intensity modulated radiation treatment (IMRT) with bone alignment, IMRT with target alignment and IMRT daily re-optimization. Treatment planning and virtual treatment delivery were performed. The delivered doses were obtained using in-house deformable dose mapping software. The results were analyzed using equivalent uniform dose (EUD).
RESULTS
With the same margin, rectum and bladder doses in IMRT plans were about 10% and 5% less than those in CRT plans, respectively. Rectum and bladder doses were reduced as much as 20% if motion margin is reduced by 1cm. IMRT is more sensitive to organ motion. Large discrepancies of bladder and rectum doses were observed compared to the actual delivered dose with treatment plan predication. The therapeutic ratio can be improved by 14% and 25% for rectum and bladder, respectively, if IMRT online re-planning is employed compared to the IMRT bone alignment approach. The improvement of target alignment approach is similar with 11% and 21% dose reduction to rectum and bladder, respectively. However, underdosing in seminal vesicles was observed on certain patients.
CONCLUSIONS
Online treatment plan re-optimization may significantly improve therapeutic ratio in prostate cancer treatments mostly due to the reduction of PTV margin. However, for low risk patient with only prostate involved, online target alignment IMRT treatment would achieve similar results as online re-planning. For all IGRT approaches, the delivered organ-at-risk doses may be significantly different from treatment planning prediction.
目的
比较各种在线图像引导放射治疗（IGRT）策略的剂量差异，并预测在线重新优化技术在前列腺癌放射治疗中的潜在益处。
材料与方法
本研究招募了9名前列腺癌患者。每位患者有一张治疗计划CT图像和10张治疗日CT图像。评估了五种不同的在线IGRT策略，包括基于骨骼配准的三维适形放疗、通过孔径变化进行三维适形重新计划、基于骨骼配准的调强放射治疗（IMRT）、基于靶区配准的IMRT以及IMRT每日重新优化。进行了治疗计划和虚拟治疗交付。使用内部可变形剂量映射软件获得所交付的剂量。使用等效均匀剂量（EUD）分析结果。
结果
在相同边界条件下，IMRT计划中直肠和膀胱的剂量分别比三维适形放疗（CRT）计划低约10%和5%。如果将运动边界减少1cm，直肠和膀胱的剂量可降低多达20%。IMRT对器官运动更敏感。与治疗计划预测的实际交付剂量相比，观察到膀胱和直肠剂量存在较大差异。与基于IMRT骨骼配准方法相比，如果采用IMRT在线重新计划，直肠和膀胱的治疗比分别可提高14%和25%。靶区配准方法的改善效果类似，直肠和膀胱剂量分别降低11%和21%。然而，在某些患者中观察到精囊剂量不足。
结论
在线治疗计划重新优化可显著提高前列腺癌治疗的治疗比，主要是由于计划靶体积（PTV）边界的减少。然而，对于仅累及前列腺的低风险患者，在线靶区配准IMRT治疗将获得与在线重新计划相似的结果。对于所有IGRT方法，所交付的危及器官剂量可能与治疗计划预测有显著差异。
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