Zhang Geoffrey, Feygelman Vladimir, Stevens Craig, Li Weiqi, Leuthold Susan, Springett Gregory, Hoffe Sarah
Division of Radiation Oncology, Moffitt Cancer Center, Tampa, FL, USA.
Med Dosim. 2011 Spring;36(1):102-8. doi: 10.1016/j.meddos.2010.01.004. Epub 2010 Mar 7.
Compared with multileaf collimator (MLC)-based intensity-modulated radiotherapy (IMRT) for moving targets, compensator-based IMRT has advantages such as shorter beam-on time, fewer monitor units with potentially decreased secondary carcinogenesis risk, better optimization-to-deliverable dose conversion, and often better dose conformity. Some of the disadvantages include additional time for the compensators to be built and delivered, as well as extra cost. Patients undergoing treatment of abdominal cancers often experience weight loss. It would be necessary to account for this change in weight with a new plan and a second set of compensators. However, this would result in treatment delays and added costs. We have developed a method to re-plan the patient using the same set of compensators. Because the weight changes seen with the treatment of abdominal cancers are usually relatively small, a new 4D computed tomography (CT) acquired in the treatment position with markers on the original isocenter tattoos can be registered to the original planning scan. The contours of target volumes from the original scans are copied to the new scan after fusion. The original compensator set can be used together with a few field-in-field (FiF) beams defined by the MLC (or beams with cerrobend blocks for accelerators not equipped with a MLC). The weights of the beams with compensators are reduced so that the FiF or blocked beams can be optimized to mirror the original plan and dose distribution. Seven abdominal cancer cases are presented using this technique. The new plan on the new planning CT images usually has the same dosimetric quality as the original. The target coverage and dose uniformity are improved compared with the plan without FiF/block modification. Techniques combining additional FiF or blocked beams with the original compensators optimize the treatment plans when patients lose weight and save time and cost compared with generating plans with a new set of compensators.
与基于多叶准直器（MLC）的调强放射治疗（IMRT）用于移动靶区相比，基于补偿器的IMRT具有一些优势，如射束开启时间更短、监测单位更少，潜在降低二次致癌风险，优化到可交付剂量的转换更好，且通常剂量适形性更好。一些缺点包括制作和交付补偿器需要额外时间以及成本增加。接受腹部癌症治疗的患者常出现体重减轻。有必要用新计划和第二套补偿器来考虑体重的这种变化。然而，这会导致治疗延迟和成本增加。我们已开发出一种使用同一套补偿器对患者重新计划的方法。由于腹部癌症治疗中出现的体重变化通常相对较小，在治疗位置采集的带有原始等中心纹身标记的新的4D计算机断层扫描（CT）可以与原始计划扫描进行配准。融合后，将原始扫描中靶区体积的轮廓复制到新扫描中。原始补偿器组可与由MLC定义的一些野中野（FiF）射束（或为未配备MLC的加速器使用铈镧合金挡块的射束）一起使用。带有补偿器的射束权重降低，以便FiF或挡块射束能够优化，以反映原始计划和剂量分布。本文展示了使用该技术的7例腹部癌症病例。新计划CT图像上的新计划通常具有与原始计划相同的剂量学质量。与未修改FiF/挡块的计划相比，靶区覆盖和剂量均匀性得到改善。当患者体重减轻时，将额外的FiF或挡块射束与原始补偿器相结合的技术可优化治疗计划，与使用新的补偿器组生成计划相比，节省了时间和成本。
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