Department of Radiation Oncology, Technical University of Munich, Klinikum rechts der Isar, Munich, Germany.
Department of Neurosurgery, Technical University of Munich, Klinikum rechts der Isar, Munich, Germany.
J Appl Clin Med Phys. 2020 Aug;21(8):6-14. doi: 10.1002/acm2.12905. Epub 2020 May 31.
Throughout the last years, carbon-fibre-reinforced PEEK (CFP) pedicle screw systems were introduced to replace standard titanium alloy (Ti) implants for spinal instrumentation, promising improved radiotherapy (RT) treatment planning accuracy. We compared the dosimetric impact of both implants for intensity modulated proton (IMPT) and volumetric arc photon therapy (VMAT), with the focus on uncertainties in Hounsfield unit assignment of titanium alloy.
Retrospective planning was performed on CT data of five patients with Ti and five with CFP implants. Carbon-fibre-reinforced PEEK systems comprised radiolucent pedicle screws with thin titanium-coated regions and titanium tulips. For each patient, one IMPT and one VMAT plan were generated with a nominal relative stopping power (SP) (IMPT) and electron density (ρ) (VMAT) and recalculated onto the identical CT with increased and decreased SP or ρ by ±6% for the titanium components.
Recalculated VMAT dose distributions hardly deviated from the nominal plans for both screw types. IMPT plans resulted in more heterogeneous target coverage, measured by the standard deviation σ inside the target, which increased on average by 7.6 ± 2.3% (Ti) vs 3.4 ± 1.2% (CFP). Larger SPs lead to lower target minimum doses, lower SPs to higher dose maxima, with a more pronounced effect for Ti screws.
While VMAT plans showed no relevant difference in dosimetric quality between both screw types, IMPT plans demonstrated the benefit of CFP screws through a smaller dosimetric impact of CT-value uncertainties compared to Ti. Reducing metal components in implants will therefore improve dose calculation accuracy and lower the risk for tumor underdosage.
在过去的几年中，碳纤维增强聚醚醚酮（CFP）椎弓根螺钉系统被引入以替代标准钛合金（Ti）植入物进行脊柱器械固定，有望提高放射治疗（RT）治疗计划的准确性。我们比较了这两种植入物对强度调制质子（IMPT）和容积弧形光子治疗（VMAT）的剂量学影响，重点是钛合金亨氏单位赋值的不确定性。
对 5 例 Ti 和 5 例 CFP 植入物患者的 CT 数据进行回顾性计划。碳纤维增强 PEEK 系统由具有薄钛涂层区域和钛花托的不透明椎弓根螺钉组成。对于每个患者，生成一个名义相对阻止本领（IMPT）和电子密度（ρ）（VMAT）的 IMPT 和一个 VMAT 计划，并根据钛部件的±6%增加或减少 SP 或 ρ，重新计算到相同的 CT 上。
对于两种螺钉类型，重新计算的 VMAT 剂量分布几乎与名义计划没有偏差。IMPT 计划导致靶区覆盖更不均匀，通过靶区内部的标准差σ来衡量，Ti 组平均增加了 7.6±2.3%，而 CFP 组增加了 3.4±1.2%。较大的 SP 导致靶区最小剂量降低，较小的 SP 导致剂量最大值升高，Ti 螺钉的影响更为明显。
虽然 VMAT 计划在两种螺钉类型的剂量学质量方面没有表现出明显差异，但 IMPT 计划通过与 Ti 相比，CFP 螺钉的 CT 值不确定性对剂量计算的影响较小，从而显示出了优势。减少植入物中的金属部件将提高剂量计算的准确性并降低肿瘤剂量不足的风险。
