【摘要】 目的 研究使用Bowtie滤线器（F1）后，保证加速器CBCT患者扫描图像质量前提下，如何合理设置扫描条件，尽量降低辐射剂量。 方法 使用Piranha辐射测量仪测量CBCT在使用F1与未使用F1时射线的半价层。设定不同的扫描模式，使用直径30 cm的有机玻璃模体测量扫描剂量，并使用XVI附带的Catphan503模体测量客观图像质量。在此基础上，研究扫描剂量以及图像质量与扫描条件的关系，提出了适合临床患者的胸部与腹部不同的扫描条件。 结果 使用F1后射束的半价层增加了0.77～0.92 mmAl，扫描剂量明显减少，中心点减少了22%~29%，边缘点减少了41%~45%，皮肤剂量减少显著。图像质量随着扫描剂量的增大而提高。空间分辨力受FOV影响较大，但一般能识别1～2 mm的物体，完全能够满足分辨细小骨结构与标记点的临床要求。图像伪影在使用L20时的大mAs下明显。胸部低剂量的CBCT图像如100 kV，M20，0.5 mAs的扫描条件亦可满足临床要求。腹部则需要使用较大剂量的扫描模式，CBCT图像才达到进行配准的要求。 结论 F1的使用在改善图像质量的前提下降低了扫描剂量，使用新的扫描序列能平衡二者的关系。【Abstract】 Objective To explore the influence of bowtie filtration on absorb dose and half-value layer inaluminum (Al) of cone-beam CT, estimate the image dose under different scan protocol, and establish the relationship between the image quality and the scan protocol after using F1. Methods Piranha was used to measure the HVL. Dose measurements were performed with an 0.6 cc Farmer type ionization chamber with a 30 cm-diam cylindrical shaped water phantoms in 100 and 120 kV with a series of mAs and FOV. CNR, noise and uniformity were measured on the Catphan503 images. Results HVL increased 0.77-0.92 mmAl where XVI generally had more penetrating beams at the similar kV settings. Scanning dose significantly reduced, the center point decreased 22%-29%, the edge with a decrease of 41%-45% which meant a very significant reduction in skin dose. Image quality improved with mAs increase. The spatial resolution mainly changed with FOV. But generally can identify 1-2 mm-diam objects, fully meet the clinical requirements of identify small bone structure and marker. Through this clinical investigation, low-dose CBCT images in chest, such as 100 kV, M20, and 0.5 mAs scanning protocol appeared to be an optimal settings. Abdomen image needed a higher dose to reach the requirements of registration. Conclusion Using F1 under the premise of improving the image quality then reducing the scanning dose and using a new scanning sequence can balance the image quality and scanning dose.
【摘要】 目的 分析重力因素对二维探测器阵列验证静态调强计划的影响，判断机架角度归为0°的测量方法是否安全可靠。 方法 在0°机架角和实际治疗机架角分别测量静态调强计划的剂量分布，以3 mm范围内偏差lt;3%(3% 3 mm)标准进行γ分析，获得相对于参考剂量分布的通过率，分析通过率变化规律。分析两种方法测量的等中心点绝对剂量的差异。 结果 通过率的变化呈随机分布，96.9%的照射野偏差lt;2.5%。所有计划的85.7%绝对剂量偏差lt;2%，最大偏差为4.75%。 结论 使用二维探测器阵列在0°角进行调强计划的日常验证是安全可靠的。【Abstract】 Objective To analyze impacts of gravity on the verification of IMRT plans with 2-Dimensional detector arrays and to evaluate the reliability of the measurements in vertical direction (gantry angle=0). Methods The dose distributions for each beam in IMRT plans were measured with 0 degree gantry angle and actual gantry angle respectively. The γ percentage pass rate (according to 3% 3 mm) for each beam under each angle condition was obtained by the comparison between the measured dose distribution and the calculated dose map from the treatment planning system which was treated as the reference distribution. Then the absolute dose at the isocenter for each plan was measured at each angle condition and was analyzed. Results The variations of γ percentage pass rates between the two types of measurements were randomly distributed, and the deviations for 96.9% beams were less than±2.5%. The differences between absolute doses for 85.7% beams were less than±2% and the biggest deviation was -4.75%. Conclusion Verification of IMRT plans for the radiotherapy quality assurance using 2-Dimensional detector arrays in 0 degree gantry angle is safe and reliable.
目的 通过非小细胞肺癌（NSCLC）图像引导放射治疗（IGRT）过程中，每次治疗前获取的锥形束CT图像，动态观察肿瘤体积的变化。 方法 2009年2月－2010年8月18例周围型NSCLC患者接受IGRT。每次治疗前进行千伏级锥形束CT（KV-CBCT）图像的采集。每周在KV-CBCT图像上勾画肿瘤靶区并计算靶区体积，经统计后分析肿瘤治疗过程中体积的变化。 结果 治疗开始时平均体积为28.5 cm3（2.5～109.1 cm3），治疗结束时平均体积为17.1 cm3 （1.4～73.4 cm3）。平均退缩率为35.9%（3.9%～68.9%），平均每天的退缩率为1.5% （0.1%～5.4%）。治疗结束时，0例病灶完全消退，1例部分消退，10例微小消退，7例稳定。 结论 治疗过程中，NSCLC肿瘤的退缩可以通过KV-CBCT进行观察。当病灶为周围型时，能对肿瘤体积的变化进行客观有效的评价。放射治疗过程中肿瘤的体积改变具有很大的异质性，肿瘤在治疗过程中体积均有一定的退缩，但治疗结束时大多数病灶仅为微小消退或稳定。