Huang Xin, Guo Chenlei, Liu Shuangtong, Men Kuo, Wang Hui
Department of Oncology, Tianjin Union Medical Center, The First Affiliated Hospital of Nankai University, Tianjin, China.
Tianjin Cancer Institute of Integrative Traditional Chinese and Western Medicine, Tianjin Union Medical Center, The First Affiliated Hospital of Nankai University, Tianjin, China.
Front Oncol. 2025 Jul 29;15:1612643. doi: 10.3389/fonc.2025.1612643. eCollection 2025.
In volumetric modulated arc therapy (VMAT), collimator angle selection impacts dose distribution and plan quality. Conventional VMAT plans use dual arcs with collimators set at 0˚. This study explores the dosimetric effects of using orthogonal collimator angles (0˚ and 90˚) in dual-arc VMAT.
Sixty patients with head and neck, thoracic, and abdominal tumors were analyzed. Two VMAT plans were generated: Plan A (0˚ collimator angle) and Plan B (0˚ and 90˚ collimator angles). Dosimetric endpoints included conformity index (CI), gradient measure (GM), homogeneity index (HI), dose to organs at risk (OARs), mean dose to normal tissues (D), monitor units (MU), and gamma pass rate (GPR).
Plan B improved dosimetric outcomes over Plan A. HI decreased by 0.03 in the rectum, 0.01 in the breast, and 0.01 in the larynx. GM decreased by 0.15 cm in the rectum, 0.05 cm in the breast, and 0.01 cm in the larynx. OAR doses were reduced across sites, with notable decreases in the bladder (-4.62 Gy), left anterior descending artery (-3.99 Gy), and spinal cord (-1.79 Gy). D was slightly reduced in the rectum, breast and larynx. MU increased in rectum plans (+41 MU), but decreased in the breast and laryngeal plans by 38 MU and approximately 73 MU, respectively. All plans achieved GPR > 95%.
Incorporating orthogonal collimator angles (0˚ and 90˚) in dual-arc VMAT enhances dose conformity and spares OARs without compromising target coverage or delivery accuracy. This approach is clinically applicable with minimal workflow changes.
在容积调强弧形放疗（VMAT）中，准直器角度的选择会影响剂量分布和计划质量。传统的VMAT计划使用双弧，准直器设置为0˚。本研究探讨在双弧VMAT中使用正交准直器角度（0˚和90˚）的剂量学效应。
分析了60例患有头颈部、胸部和腹部肿瘤的患者。生成了两个VMAT计划：计划A（准直器角度为0˚）和计划B（准直器角度为0˚和90˚）。剂量学终点包括适形指数（CI）、梯度测量值（GM）、均匀性指数（HI）、危及器官（OAR）的剂量、正常组织的平均剂量（D）、监测单位（MU）和伽马通过率（GPR）。
计划B比计划A改善了剂量学结果。直肠的HI降低了0.03，乳腺降低了0.01，喉降低了0.01。直肠的GM降低了0.15 cm，乳腺降低了0.05 cm，喉降低了0.01 cm。各部位的OAR剂量均降低，膀胱（-4.62 Gy）、左前降支动脉（-3.99 Gy）和脊髓（-1.79 Gy）有显著降低。直肠、乳腺和喉的D略有降低。直肠计划的MU增加（+41 MU），但乳腺和喉计划的MU分别降低了38 MU和约73 MU。所有计划的GPR均>95%。
在双弧VMAT中纳入正交准直器角度（0˚和90˚）可提高剂量适形性并保护OAR，而不影响靶区覆盖或照射准确性。这种方法在临床工作流程变化最小的情况下即可应用。
