Riley Catalina, Cox Christopher, Graham Sasha, Havran Holly, Kramer Bethany, Netherton Tucker, Peterson Christine, Williamson Tyler, Court Laurence
The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Med Dosim. 2018 Sep 6. doi: 10.1016/j.meddos.2018.06.004.
The Varian Halcyon linear accelerator is designed for faster treatment time and fewer treatment errors than conventional linear accelerators. Its increased gantry speed (4 rpm), dose rate (800 MU/min), and leaf speed (5 cm/s) reduce treatment time. The 2 multileaf collimator banks of 1 cm leaf width could cause planning difficulties, but utilizing many arcs could address this challenge. While 3 or more arcs are often avoided due to the increased treatment time, the Halcyon can deliver 5 arcs in under 3 minutes. For prostate and head-and-neck, we hypothesized plan quality would increase with increasing arcs without compromising treatment time. Fifteen prostate and fifteen head-and-neck previously treated patients were replanned to 78 and 66 Gy, respectively. A total of 150 volumetric modulated arc therapy (VMAT) plans, ranging from 1 to 5 arcs, were created to compare organ-at-risk (OAR) sparing, target coverage, homogeneity, and hotspot volume. Plans were normalized to the prescribed dose of 98% and 95% of the primary target volume for prostate and head-and-neck, respectively. All prostate 4-arc and 5-arc plans met MD Anderson Cancer Center (MDACC) constraints, while 86.7%, 20%, and 6.7% of the 1-arc, 2-arc, and 3-arc plans did not meet constraints, respectively. As the number of arcs increased, all OAR maximum doses decreased. All head-and-neck 5-arc plans met MDACC constraints, while 73.3%, 26.7%, 13.3%, and 6.7% of the 1-arc, 2-arc, 3-arc, and 4-arc plans did not meet constraints, respectively. The contralateral parotid mean dose and the spinal cord maximum dose decreased with increasing arcs. Homogeneity and conformity indices decreased when increasing from 1 to 5 arcs for both prostate and head-and-neck. Overall, homogeneity and conformity indices and OAR doses improved when using three or more arcs. Therefore, using at least 3 arcs for VMAT plans on the Halcyon will increase plan quality without compromising treatment time.
瓦里安Halcyon直线加速器的设计目的是，相较于传统直线加速器，实现更短的治疗时间和更少的治疗误差。其提升的机架转速（4转/分钟）、剂量率（800 MU/分钟）和叶片速度（5厘米/秒）缩短了治疗时间。两片叶宽为1厘米的多叶准直器可能会导致计划制定困难，但采用多个弧可以应对这一挑战。虽然由于治疗时间增加，通常会避免使用3个或更多弧，但Halcyon可以在3分钟内完成5个弧的照射。对于前列腺癌和头颈癌，我们假设在不影响治疗时间的情况下，计划质量会随着弧数的增加而提高。对15例先前接受过治疗的前列腺癌患者和15例头颈癌患者分别重新制定计划，剂量分别为78 Gy和66 Gy。总共创建了150个容积调强弧形治疗（VMAT）计划，弧数从1个到5个不等，以比较危及器官（OAR）的保护情况、靶区覆盖、均匀性和热点体积。计划分别针对前列腺癌和头颈癌的主要靶区体积的规定剂量的98%和95%进行归一化。所有前列腺癌的4弧和5弧计划均符合MD安德森癌症中心（MDACC）的限制条件，而1弧计划、2弧计划和3弧计划分别有86.7%、20%和6.7%不符合限制条件。随着弧数的增加，所有OAR的最大剂量均降低。所有头颈癌的5弧计划均符合MDACC的限制条件，而1弧计划、2弧计划、3弧计划和4弧计划分别有73.3%、26.7%、13.3%和6.7%不符合限制条件。随着弧数增加，对侧腮腺平均剂量和脊髓最大剂量降低。对于前列腺癌和头颈癌，从1弧增加到5弧时，均匀性指数和适形指数均降低。总体而言，使用3个或更多弧时均匀性指数、适形指数和OAR剂量均得到改善。因此，在Halcyon上进行VMAT计划时使用至少3个弧将提高计划质量，同时不影响治疗时间。
