瓦里安 OBI CBCT 系统在乳腺癌患者摆位中的临床应用及剂量降低技术

Department of Radiation Oncology, Dana Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, Massachusetts 02115, USA.

Med Phys. 2010 Jun;37(6):2985-98. doi: 10.1118/1.3432617.

PURPOSE

To characterize the standard modes of Varian on board imaging (OBI) v1.4 system and identify techniques to further optimize imaging parameters, in particular, for breast treatment setup.

METHODS

A male anthropomorphic torso phantom was used for image quality assessment and a simpler thorax phantom for dose measurements. Both phantoms had artificial breasts attached. Doses were measured with an ion chamber in seven locations in the thorax and the breast. Evaluation of image quality was performed in terms of contrast-to-noise ratio (CNR) and in combination with the dose-to-contrast-to-noise (CNRD) parameter. The effect of kVp and mAs on the image quality, dose, and CNRD parameter was analyzed. In addition, image geometry with noncentral isocenter location with start and stop imaging angles adjusted for greater sparing of the contralateral breast was evaluated in terms of image quality and dose.

RESULTS

The measurements showed doses between 0.02 and 1.6 cGy for the three full-fan modes and 0.6-3.2 cGy for half-fan modes. This is a reduction of over 80% and 30%-50% compared to OBI v.1.3 modes for full-fan and half-fan modes, respectively. The CNRD is the highest for both low dose modes (low dose thorax and low dose head). Optimal ranges for an averaged sized thorax are tube voltages not higher than 100 kVp and current-time products between 100 and 400 mAs. For the contralateral breast and lung, a dose less than 0.03 cGy per scan was measured for the optimized image geometry with the noncentral isocenter location.

CONCLUSIONS

The OBI v1.4 system allows for imaging with a larger variety of imaging parameters compared to previous OBI v1.3 systems. The largest doses (up to 4 cGy) were measured in a phantom when OBI v1.4 system was used for imaging with half-fan modes. Using full-fan modes resulted in the doses less than 1.6 cGy. Further decrease in dose may be achieved by reducing mAs while preserving acceptable image quality. Organ specific sparing (e.g., contralateral breast) may be achieved by proper selection of the start and stop angles. For thorax imaging, the use of Low Dose Thorax mode is recommended.

目的

描述瓦里安 onboard 成像（OBI）v1.4 系统的标准模式，并确定进一步优化成像参数的技术，特别是用于乳房治疗设置。

方法

使用男性人体体模进行图像质量评估，使用更简单的胸部体模进行剂量测量。两个体模都附有人工乳房。在胸部和乳房的七个位置用离子室测量剂量。使用对比度噪声比（CNR）和结合剂量-对比度噪声比（CNRD）参数评估图像质量。分析了千伏和毫安秒对图像质量、剂量和 CNRD 参数的影响。此外，还评估了非中心等中心位置的图像几何形状，并调整了起始和停止成像角度，以更好地保护对侧乳房，以评估图像质量和剂量。

结果

测量结果显示，三种全扇区模式的剂量在 0.02 至 1.6 cGy 之间，半扇区模式的剂量在 0.6 至 3.2 cGy 之间。与 OBI v.1.3 模式相比，全扇区和半扇区模式的剂量分别降低了 80%以上和 30%-50%。CNRD 对于低剂量模式（低剂量胸部和低剂量头部）最高。对于平均大小的胸部，最佳的管电压范围不高于 100 kVp，电流时间乘积在 100 至 400 mAs 之间。对于对侧乳房和肺，使用非中心等中心位置的优化图像几何形状，每个扫描的剂量小于 0.03 cGy。

结论

与之前的 OBI v1.3 系统相比，OBI v1.4 系统允许使用更多种类的成像参数进行成像。当使用半扇区模式进行成像时，在体模中测量到最大剂量（高达 4 cGy）。使用全扇区模式的剂量小于 1.6 cGy。通过降低毫安秒同时保持可接受的图像质量，可以进一步降低剂量。通过适当选择起始和停止角度，可以实现特定器官的保护（例如对侧乳房）。对于胸部成像，建议使用低剂量胸部模式。