Ziemann Christian, Cremers Florian, Motisi Laura, Albers Dirk, MacPherson Miller, Rades Dirk
Department of Radiotherapy, University Medical Center Schleswig Holstein/Campus Luebeck, Luebeck, Germany.
Department of Radiotherapy, University Medical Center Schleswig Holstein/Campus Luebeck, Luebeck, Germany.
Med Dosim. 2024;49(2):93-101. doi: 10.1016/j.meddos.2023.08.011. Epub 2023 Oct 3.
This study presents a new treatment planning approach merging 3D-CRT and VMAT fields into a hybrid treatment plan (HybTP), in order to achieve an optimum dose coverage of the planning target volume (PTV) and protection of OAR. Craniospinal axis irradiation (CSI) treated with 3D conformal radiotherapy (3D-CRT) is associated with high doses to the heart and eye lenses but provides better sparing of lungs and kidneys compared to volumetric modulated arc therapy (VMAT). VMAT treatment spares eye lenses and the heart, but lungs and kidneys are not as effective as 3D-CRT. Thus, a combination of both techniques (HybTP) may be optimal in sparing all these organs at risk (OAR). The results of HybTP are compared with helical tomotherapy (HT), intensity modulated radio therapy (IMRT), VMAT, and 3D-CRT plans. Hybrid, HT, VMAT, IMRT, and 3D-CRT treatment plans for a male child (age 6 years) with medulloblastoma were created and compared. A total dose of 35.2 Gy (PTV) with a dose per fraction of 1.6 Gy was prescribed. The following dose acceptance criteria were defined: The plans were compared regarding dose homogeneity index (HI) and conformity index (CI), PTV coverage, (particularly at cribriform plate) and doses at OARs. Best conformity was achieved with HT (CI = 0.98) followed by VMAT (CI = 0.96), IMRT (CI = 0.91), HybTP (CI = 0.86), and 3D-CRT (CI = 0.83). The homogeneity index varied marginally. For both HT and IMRT the HI was 0.07, and for 3D-CRT, VMAT and HybTP the HI was between 0.13 and 0.15. The cribriform plate was sufficiently covered by HybTP, VMAT, and 3D-CRT. The dose acceptance criteria for OARs were met by HT and HybTP. VMAT did not meet the criteria for lung (D = right 10.4 Gy/left 10.2 Gy), 3D-CRT did not meet the criteria for eye lenses (D = right 32.3 Gy/left 33.1), and heart (V≈44%) and IMRT did not meet the criteria for lung (D = right 11.1 Gy/left 11.2 Gy) and eye lenses (D = right 12.2 Gy/left 13.1). HybTP meets all defined acceptance criteria and has proved to be a reasonable alternative for CSI. With HybTP that combines VMAT at the brain and heart with 3D-CRT posterior spinal fields (to spare lungs and kidneys), both appropriate coverage of the PTV and sparing of OAR can be achieved.
本研究提出了一种新的治疗计划方法，即将三维适形放疗（3D-CRT）和容积调强弧形放疗（VMAT）野合并为一个混合治疗计划（HybTP），以实现计划靶体积（PTV）的最佳剂量覆盖并保护危及器官（OAR）。采用三维适形放疗（3D-CRT）治疗的颅脊柱轴照射（CSI）会使心脏和晶状体受到高剂量照射，但与容积调强弧形放疗（VMAT）相比，对肺和肾脏的保护更好。VMAT治疗可使晶状体和心脏免受高剂量照射，但对肺和肾脏的保护效果不如3D-CRT。因此，两种技术相结合（HybTP）可能是保护所有这些危及器官（OAR）的最佳选择。将HybTP的结果与螺旋断层放疗（HT）、调强放疗（IMRT）、VMAT和3D-CRT计划进行了比较。为一名患有髓母细胞瘤的男童（6岁）制定并比较了混合、HT、VMAT、IMRT和3D-CRT治疗计划。处方总剂量为35.2 Gy（PTV），每次分割剂量为1.6 Gy。定义了以下剂量接受标准：比较各计划的剂量均匀性指数（HI）和适形指数（CI）、PTV覆盖情况（特别是在筛板处）以及OAR处的剂量。HT的适形性最佳（CI = 0.98），其次是VMAT（CI = 0.96）、IMRT（CI = 0.91）、HybTP（CI = 0.86）和3D-CRT（CI = 0.83）。均匀性指数变化不大。HT和IMRT的HI均为0.07，3D-CRT、VMAT和HybTP的HI在0.13至0.15之间。HybTP、VMAT和3D-CRT对筛板的覆盖充分。HT和HybTP符合OAR的剂量接受标准。VMAT不符合肺的标准（右肺D = 10.4 Gy/左肺D = 10.2 Gy），3D-CRT不符合晶状体的标准（右晶状体D = 32.3 Gy/左晶状体D = 33.1 Gy）以及心脏的标准（V≈44%），IMRT不符合肺的标准（右肺D = 11.1 Gy/左肺D = 11.2 Gy）和晶状体的标准（右晶状体D = 12.2 Gy/左晶状体D = 13.1 Gy）。HybTP符合所有定义的接受标准，已被证明是CSI的合理替代方案。通过将脑和心脏部位的VMAT与脊柱后野的3D-CRT相结合的HybTP（以保护肺和肾脏），可以实现PTV的适当覆盖和OAR的保护。
