Department of Clinical Oncology, The University of Hong Kong, China.
Radiother Oncol. 2012 Sep;104(3):317-23. doi: 10.1016/j.radonc.2012.03.013. Epub 2012 Apr 30.
Significant tumor shrinkage and weight loss may occur during Intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). This study aims to evaluate the dosimetric effect of volumetric changes on target volumes and organs at risk (OARs) during IMRT, using reassessment of computed tomography (CT) and magnetic resonance imaging (MRI).
Nineteen loco-regionally advanced NPC patients treated with IMRT were recruited prospectively. Repeat planning CT and MRI were acquired at 30 and 50 Gy intervals. Recontouring of target volumes and OARs was based on the fused CT-MRI images. Hybrid plans with recontouring were generated. The assessment of volumetric and dosimetric changes was performed by comparing the hybrid plans with the original plan.
There was volume reduction of target volumes and parotid glands over the course of IMRT. Relative to the original plan, the hybrid plans demonstrated significantly higher dose to most of target volumes with greater dose inhomogeneity, higher maximum doses to the spinal cord and brainstem, and higher median doses to the parotid glands.
Replanning with repeat CT and MRI scans at 30 Gy is essential to keep a satisfactory dose to the target volumes and avoid overdosing the OARs.
调强放疗（IMRT）治疗鼻咽癌（NPC）时，肿瘤可能会明显缩小和患者体重减轻。本研究旨在通过重新评估 CT 和 MRI，评估靶区和危及器官（OARs）在 IMRT 期间体积变化对剂量的影响。
前瞻性纳入 19 例局部晚期 NPC 患者，接受 IMRT 治疗。在 30 和 50 Gy 时采集重复计划 CT 和 MRI。基于融合 CT-MRI 图像重新勾画靶区和 OARs。生成重新勾画的混合计划。通过比较混合计划与原始计划来评估体积和剂量变化。
在 IMRT 过程中，靶区和腮腺体积减少。与原始计划相比，混合计划显示大部分靶区的剂量明显更高，剂量不均匀性更大，脊髓和脑干的最大剂量更高，腮腺的中位数剂量更高。
在 30 Gy 时进行重复 CT 和 MRI 扫描以重新计划对于保持靶区满意剂量和避免 OARs 过度剂量至关重要。
