Babic Steven, Battista Jerry, Jordan Kevin
Department of Physics and Engineering, London Regional Cancer Program at London Health Sciences Centre, London, ON, Canada.
Int J Radiat Oncol Biol Phys. 2008 Mar 15;70(4):1281-91. doi: 10.1016/j.ijrobp.2007.11.032.
To extend the Radiological Physics Centre (RPC) intensity-modulated radiation therapy dose verification protocol to three dimensions using optical computed tomography (CT) scans of ferrous xylenol-orange (FX) gels.
The dosimetry insert in the RPC head-and-neck phantom was replaced with an FX cylindrical gel dosimeter. Two gels were calibrated, independently irradiated with 6-MV X-ray beams and scanned using laser and cone-beam (Vista) optical CT, respectively. For matching dose slices, measured dose distributions were compared with Pinnacle3 computed distributions.
Within high-dose regions and low gradients, doses measured using laser CT were 2% to 3% less than the computed dose, whereas with cone-beam CT they were 4% to 5% less. Inside the central 90% of the gel cylinder diameter, the fraction of voxels satisfying the two-dimensional gamma analysis (5% dose difference, 3-mm distance to agreement) with laser-beam- and cone-beam-measured dose distributions were 98.4% and 99.0%, respectively. A three-dimensional gamma analysis with cone-beam data revealed that 96.7% of voxels within the central 90% gel volume satisfied the above criteria. Within the axial and sagittal planes through the primary planning target volume (PTV), computed and measured doses using GAFChromicEBT film (RPC measured) and cone-beam scanned FX gel generally agreed. At equivalent points in the planning target volumes, computed, thermoluminescent dosimeter (RPC-measured), and gel point doses agreed to within 5.1% in absolute dose.
Laser and cone-beam CT yield comparable dose distributions in high-dose regions. The RPC head phantom and optical CT-scanned FX gels can be used for accurate intensity-modulated radiation therapy dose verification in three dimensions.
使用亚铁二甲酚橙（FX）凝胶的光学计算机断层扫描（CT），将放射物理中心（RPC）的调强放射治疗剂量验证方案扩展到三维。
RPC头颈模体中的剂量测定插入物被一个FX圆柱形凝胶剂量计取代。对两个凝胶进行校准，分别用6兆伏X射线束独立照射，并分别使用激光和锥束（Vista）光学CT进行扫描。对于匹配的剂量切片，将测量的剂量分布与Pinnacle3计算的分布进行比较。
在高剂量区域和低梯度范围内，使用激光CT测量的剂量比计算剂量低2%至3%，而使用锥束CT测量的剂量则低4%至5%。在凝胶圆柱体直径中心的90%范围内，满足二维伽马分析（剂量差异5%，距离一致性3毫米）的激光束和锥束测量剂量分布的体素比例分别为98.4%和99.0%。对锥束数据进行三维伽马分析表明，在中心90%凝胶体积内，96.7%的体素满足上述标准。在通过主要计划靶区（PTV）的轴向和矢状面内，使用GAFChromicEBT胶片（RPC测量）和锥束扫描的FX凝胶计算和测量的剂量总体上一致。在计划靶区内的等效点处，计算剂量、热释光剂量计（RPC测量）和凝胶点剂量在绝对剂量上的一致性在5.1%以内。
激光和锥束CT在高剂量区域产生可比的剂量分布。RPC头部模体和光学CT扫描的FX凝胶可用于三维精确调强放射治疗剂量验证。
