Medical Physics Graduate Program, Duke University, Durham, NC, USA.
Phys Med Biol. 2013 Nov 7;58(21):7791-801. doi: 10.1088/0031-9155/58/21/7791. Epub 2013 Oct 18.
There is significant interest in delivering precisely targeted small-volume radiation treatments, in the pre-clinical setting, to study dose-volume relationships with tumour control and normal tissue damage. For these studies it is vital that image guidance systems and target positioning are accurately aligned (IGRT), in order to deliver dose precisely and accurately according to the treatment plan. In this work we investigate the IGRT targeting accuracy of the X-RAD 225 Cx system from Precision X-Ray using high-resolution 3D dosimetry techniques. Small cylindrical PRESAGE® dosimeters were used with optical-CT readout (DMOS) to verify the accuracy of 2.5, 1.0, and 5.0 mm X-RAD cone attachments. The dosimeters were equipped with four target points, visible on both CBCT and optical-CT, at which a 7-field coplanar treatment plan was delivered with the respective cone. Targeting accuracy (distance to agreement between the target point and delivery isocenter) and cone alignment (isocenter precision under gantry rotation) were measured using the optical-CT images. Optical-CT readout of the first 2.5 mm cone dosimeter revealed a significant targeting error of 2.1 ± 0.6 mm and a cone misalignment of 1.3 ± 0.1 mm. After the IGRT hardware and software had been recalibrated, these errors were reduced to 0.5 ± 0.1 and 0.18 ± 0.04 mm respectively, within the manufacturer specified 0.5 mm. Results from the 1.0 mm cone were 0.5 ± 0.3 mm targeting accuracy and 0.4 ± 0.1 mm cone misalignment, within the 0.5 mm specification. The results from the 5.0 mm cone were 1.0 ± 0.2 mm targeting accuracy and 0.18 ± 0.06 mm cone misalignment, outside of accuracy specifications. Quality assurance of small field IGRT targeting and delivery accuracy is a challenging task. The use of a 3D dosimetry technique, where targets are visible on both CBCT and optical-CT, enabled identification and quantification of a targeting error in 3D. After correction, the targeting accuracy of the irradiator was verified to be within 0.5 mm (or 1.0 mm for the 5.0 mm cone) and the cone alignment was verified to be within 0.2 mm (or 0.4 mm for the 1.0 mm cone). The PRESAGE®/DMOS system proved valuable for end-to-end verification of small field IGRT capabilities.
人们对精确靶向小体积放射治疗非常感兴趣，在临床前环境中，研究肿瘤控制和正常组织损伤的剂量-体积关系。对于这些研究，至关重要的是图像引导系统和目标定位要精确对准（IGRT），以便根据治疗计划精确和准确地输送剂量。在这项工作中，我们使用高分辨率 3D 剂量测定技术研究了 Precision X-Ray 的 X-RAD 225 Cx 系统的 IGRT 靶向准确性。使用带有光学 CT 读取（DMOS）的小圆柱形 PRESAGE®剂量计来验证 2.5、1.0 和 5.0mm X-RAD 圆锥附件的准确性。剂量计配备了四个目标点，在 CBCT 和光学 CT 上都可见，分别用相应的圆锥体输送 7 野共面治疗计划。使用光学 CT 图像测量了靶向精度（目标点与输送等中心的距离协议）和圆锥体对准度（在旋转机架下的等中心精度）。使用光学 CT 读取第一个 2.5mm 圆锥体剂量计，发现明显的靶向误差为 2.1±0.6mm，圆锥体错位为 1.3±0.1mm。在对 IGRT 硬件和软件进行重新校准后，这些误差分别降低至 0.5±0.1mm 和 0.18±0.04mm，在制造商规定的 0.5mm 范围内。1.0mm 圆锥体的结果为 0.5±0.3mm 靶向精度和 0.4±0.1mm 圆锥体错位，在 0.5mm 规格范围内。5.0mm 圆锥体的结果为 1.0±0.2mm 靶向精度和 0.18±0.06mm 圆锥体错位，超出了精度规格。小型 IGRT 靶向和输送精度的质量保证是一项具有挑战性的任务。使用三维剂量测定技术，其中目标在 CBCT 和光学 CT 上都可见，使我们能够在三维空间中识别和量化靶向误差。在纠正后，辐照器的靶向精度被验证在 0.5mm 以内（对于 5.0mm 圆锥体为 1.0mm），并且圆锥体对准度被验证在 0.2mm 以内（对于 1.0mm 圆锥体为 0.4mm）。PRESAGE®/DMOS 系统对于小型 IGRT 能力的端到端验证非常有价值。
