Department of Radiation Oncology, Kinki University Faculty of Medicine, Osaka-Sayama, Japan.
Radiother Oncol. 2013 Jan;106(1):85-9. doi: 10.1016/j.radonc.2012.11.005. Epub 2013 Jan 19.
The aim of this study was to show the benefit of a two-step intensity modulated radiotherapy (IMRT) method by examining geometric and dosimetric changes.
Twenty patients with pharyngeal cancers treated with two-step IMRT combined with chemotherapy were included. Treatment-planning CT was done twice before IMRT (CT-1) and at the third or fourth week of IMRT for boost IMRT (CT-2). Transferred plans recalculated initial plan on CT-2 were compared with the initial plans on CT-1. Dose parameters were calculated for a total dose of 70 Gy for each plan.
The volumes of primary tumors and parotid glands on CT-2 regressed significantly. Parotid glands shifted medially an average of 4.2mm on CT-2. The mean doses of the parotid glands in the initial and transferred plans were 25.2 Gy and 30.5 Gy, respectively. D(2) (dose to 2% of the volume) doses of the spinal cord were 37.1 Gy and 39.2 Gy per 70 Gy, respectively. Of 15 patients in whom xerostomia scores could be evaluated 1-2 years after IMRT, no patient complained of grade 2 or more xerostomia.
This two-step IMRT method as an adaptive RT scheme could adapt to changes in body contour, target volumes and risk organs during IMRT.
本研究旨在通过观察几何和剂量学变化，展示两步调强放疗（IMRT）方法的优势。
纳入 20 例接受两步调强放疗联合化疗的咽癌患者。在 IMRT 前（CT-1）和 IMRT 第 3 或第 4 周进行 boost IMRT 时（CT-2）进行两次治疗计划 CT。将在 CT-2 上重新计算的转移计划与 CT-1 上的初始计划进行比较。为每个计划计算了总剂量为 70Gy 的剂量参数。
CT-2 上原发肿瘤和腮腺的体积明显缩小。腮腺在 CT-2 上平均向内移动 4.2mm。初始和转移计划中腮腺的平均剂量分别为 25.2Gy 和 30.5Gy。脊髓的 D2（体积的 2%所接受的剂量）剂量分别为 37.1Gy 和 39.2Gy/70Gy。在接受 IMRT 1-2 年后可评估口干评分的 15 例患者中，无患者出现 2 级或更高级别的口干。
作为适应性放疗方案的两步调强放疗方法可以适应 IMRT 期间的身体轮廓、靶体积和风险器官的变化。
