Multi‐isocenter volumetric modulated arc therapy (VMAT) is recommended for craniospinal irradiation (CSI) to smooth the dose distribution in the junction regions relying solely on inverse optimization. However, few studies have measured the dosimetric impact of setup errors on this multi‐isocenter VMAT in the junction areas. The purpose of this study is to evaluate the impact of positional errors during VMAT CSI with two‐dimension (2D) and three‐dimension (3D) dosimetric measurements. A total of 20 patients treated by three‐isocenter VMAT CSI were retrospectively reviewed and analyzed. A 3D diode array ArcCHECK and radiochromic film EBT3 were applied to measure the percentage gamma passing rates (%GPs) and dose distributions in the junction areas between the cranial/upper‐spinal and the upper/lower‐spinal fields with intentionally introduced setup errors of ± 1 mm, ±2 mm, ±3 mm, ±5 mm, and ± 8 mm, respectively. The length and volume of planning target volume (PTV) for these CSI patients ranged from 50.14 to 80.8 cm, and 1572.3 to 2114.5 cm³, respectively. The %GPs for ±3 mm, ±5 mm, and ±8 mm positional errors were around 95%, 90%, and 85%, respectively, in the junction areas. The dosimetric verification results with EBT3 films indicated that cold and hot areas were observed with the increase of introduced setup errors. In conclusion, the dosimetric verification with intentionally introduced setup errors demonstrated that positional errors within 3 mm have a little impact for VMAT CSI, although setup errors should be minimized. Relying on the inverse optimization of VMAT to smooth the dose distribution in the junction areas is feasible for CSI.

中文翻译：

---

摆位误差对颅脊椎照射多等中心容积调制弧治疗的影响

多等中心容积调制弧治疗（VMAT）被推荐用于颅脊髓照射（CSI），以平滑交界区的剂量分布，仅依靠逆优化。然而，很少有研究测量设置误差对连接区域中这种多等中心 VMAT 的剂量学影响。本研究的目的是通过二维 (2D) 和三维 (3D) 剂量测量来评估 VMAT CSI 期间位置误差的影响。回顾性分析了三等中心VMAT CSI治疗的20例患者。应用 3D 二极管阵列 ArcCHECK 和放射变色膜 EBT3 来测量颅/上脊髓和上/​​下脊髓野之间的交界处的伽马通过率百分比 (%GPs) 和剂量分布，故意引入的设置误差为分别为 ± 1 毫米、±2 毫米、±3 毫米、±5 毫米和 ± 8 毫米。这些 CSI 患者的计划目标体积 (PTV) 的长度和体积范围为 50.14 至 80.8 cm，以及 1572.3 至 2114.5 cm³，分别。±3 mm、±5 mm 和 ±8 mm 位置误差的 %GP 在接合区分别约为 95%、90% 和 85%。EBT3 薄膜的剂量验证结果表明，随着引入的设置误差的增加，观察到冷区和热区。总之，有意引入设置误差的剂量验证表明，3 mm 以内的位置误差对 VMAT CSI 的影响很小，但应尽量减少设置误差。依靠 VMAT 的逆优化来平滑交界区的剂量分布对于 CSI 是可行的。