Northern Centre for Cancer Care, Newcastle Upon Tyne Hospitals NHS Foundation Trust, Newcastle, UK.
Northern Centre for Cancer Care, Newcastle Upon Tyne Hospitals NHS Foundation Trust, Newcastle, UK.
Radiother Oncol. 2019 Apr;133:100-105. doi: 10.1016/j.radonc.2018.12.029. Epub 2019 Jan 22.
Magnetic Resonance (MR)-only prostate radiotherapy has recently been clinically implemented using commercial synthetic Computed Tomography (sCT) algorithms. However patients with hip prostheses have been excluded from all MR-only research to date and assumed to require dedicated sCT algorithms. This study aimed to investigate the dosimetric accuracy of applying a commercial sCT algorithm, based on an atlas of patients without hip prostheses, to patients with prostheses.
18 patients with unilateral hip prostheses received MR and CT scans in the radiotherapy position. sCTs were generated from the MR using a commercial algorithm. The clinical Volumetric Modulated Arc Therapy (VMAT) plan, consisting of partial arcs which avoided the prosthesis, was recalculated using the sCT and the dose distribution compared.
The mean isocentre dose difference was ΔD = (-0.4 ± 0.2)% (mean ± standard error of the mean (sem), range - 1.9%, 1.1%) and the mean differences in Planning Target Volume, bladder and rectum mean doses were ≤0.3%. The 3D global gamma pass rate with dose difference 1% and distance to agreement 1 mm within the body was Γ = (95.0 ± 0.5)% (sem) and within the 50% isodose volume, which excluded the prosthesis, was Γ = (98.5 ± 0.4)% (sem). The pass rate within the PTV was Γ ≥ 99.7% for all patients, although for PTVs close (≤3.5 cm) to the prosthesis Γ < 85% for three patients. The sCT did not accurately represent the prosthesis with a mean difference in radiological isocentre depth near the prosthesis of Δd = (15.8 ± 2.6) mm (sem). However inside the treatment plan arc the difference was Δd = (-1.8 ± 0.5) mm (sem).
Using a commercial prostate sCT algorithm for patients with unilateral hip prostheses is dosimetrically accurate (<0.5%) as long as the routine prosthesis-avoidance treatment planning approach is used and the PTV is >3.5 cm from the prosthesis. This suggests MR-only prostate radiotherapy can be extended to patients with hip prostheses without requiring a specific sCT algorithm.
磁共振（MR）仅前列腺放射治疗最近已在临床中使用商业合成计算机断层扫描（sCT）算法实施。然而，迄今为止，所有仅使用磁共振的研究都排除了装有髋关节假体的患者，并假定需要使用专门的 sCT 算法。本研究旨在研究使用基于无髋关节假体患者图谱的商业 sCT 算法为装有假体的患者进行剂量计算的准确性。
18 例单侧髋关节假体患者在放射治疗位置接受 MR 和 CT 扫描。使用商业算法从 MR 生成 sCT。重新计算了包括避开假体的部分弧形的临床容积调强弧形治疗（VMAT）计划，并比较了剂量分布。
平均等中心点剂量差异为 ΔD=（-0.4±0.2）%（平均值±标准误差（sem），范围为-1.9%，1.1%），计划靶区（PTV）、膀胱和直肠平均剂量的差异均≤0.3%。在体内 1%剂量差异和 1mm 距离一致性的三维全局伽玛通过率为 Γ=（95.0±0.5）%（sem），在排除假体的 50%等剂量体积内为 Γ=（98.5±0.4）%（sem）。对于所有患者，PTV 内的通过率均≥99.7%，尽管对于靠近假体（≤3.5cm）的 PTV，有 3 名患者的通过率<85%。sCT 并不能准确地表示假体，假体附近的放射学等中心点深度的平均差异为 Δd=（15.8±2.6）mm（sem）。然而，在治疗计划弧形内，差异为 Δd=（-1.8±0.5）mm（sem）。
只要使用常规的假体回避治疗计划方法，并且 PTV 距离假体>3.5cm，使用商业前列腺 sCT 算法为单侧髋关节假体患者进行治疗的剂量计算是准确的（<0.5%）。这表明，无需特定的 sCT 算法即可将仅使用磁共振的前列腺放射治疗扩展到装有髋关节假体的患者。
