Digital tomosynthesis: a new paradigm for radiation treatment verification

描述(申请人提供)：三维适形放射治疗的治疗体积和计划体积之间的任何偏差，如调强放射治疗，都可能导致不良的临床结果。因此，在辐射传递之前立即使用机载(或实时)程序将所有潜在偏差降至最低是至关重要的。目前，治疗验证通常采用常规的二维放射成像和先进的三维锥束CT(CBCT)。然而，二维放射学验证主要基于骨骼结构和/或植入的基准，对于软组织目标是次优的。虽然机载CBCT可以提供三维软组织信息，但它有三个主要限制：1)机载CBCT的采集时间限制在60秒(~15个呼吸周期)，使得单次屏气成像不适用于表现呼吸运动的器官；2)360°机械清晰度的CBCT采集可能会限制大型患者、周围肿瘤(如乳房)或有实质性固定或支撑装置的患者使用CBCT；3)用目前的成像技术，高辐射剂量(2-9cGy值)被传递到成像体积，这对于日常成像是不可取的，对于那些有发展为第二种恶性肿瘤的高风险的人来说，这可能是一个特别的问题。为了克服这些局限性，我们提出了一种创新的数字断层合成(DTS)成像技术用于三维目标定位。虽然DTS技术已被用于数字胸部和乳房X光检查，但其在目标定位中的应用尚不清楚。DTS只需要有限的门架旋转(例如，扫描角度为40度或更小)即可重建3-D解剖信息。因此，与CBCT相比，成像时间和剂量大大减少，使屏气DTS成为日常运动器官成像的简单解决方案。此外，DTS所需的机械间隙减少，使其比CBCT更适用。目前，DTS技术在治疗验证中的定位精度尚不清楚。这一方案假设使用DTS技术的目标定位精度优于二维X线片，与CBCT相当，但成像时间和剂量更少，机械间隙更好。为了验证这一假设，目标1旨在确定4个解剖部位的最佳DTS扫描角度：头颈部、胸部、腹部和骨盆。较小的扫描角度对于成像效率是可取的，但对于图像质量则不是那么可取的。因此，我们将使用4个解剖部位的患者数据，评估扫描角度对(A)DTS模体的对比度噪声比和分辨率以及(B)DTS和CBCT切片之间共享的互信息的影响。在目标2中，我们将使用4个解剖部位的患者数据，定量比较基于DTS的靶点定位精度与2-D X线片和CBCT的定位精度。为了实现这一目标，三名医生将使用2-D、DTS、CBCT技术测量参考图像和机载图像之间的相对移位和旋转。我们预计，DTS目标定位的精度将与CBCT相当，并比二维放射成像有所改善。然而，我们希望DTS在日常的3-D靶点定位中比全CBCT更实用、更有效、提供更低的剂量。放射治疗射束与肿瘤靶点的准确对准对于切除肿瘤和保护周围健康组织至关重要。目前，机载锥束CT(CBCT)是对准乳房、肺部、下腹部等软组织肿瘤的最佳方法，但其采集时间长、机械清除要求高、辐射剂量大等缺点限制了其在放射治疗靶点定位中的应用。有些是很难改进的，因为传统的直线加速器有门架转速的限制。我们提出的数字断层合成(DTS)方法将通过更短的采集时间、更少的机械约束和更低的辐射剂量来提供更广泛和更常规适用的软组织对齐。这种更频繁、范围更广的应用将转化为更一致地消除肿瘤，并减少对附近健康组织的损害。

DESCRIPTION (provided by applicant): Any deviation between treated and planned volume for 3-D conformal therapy, such as IMRT, may cause an adverse clinical outcome. It is therefore critical to minimize all potential deviations using an on-board (or real- time) procedure immediately prior to radiation delivery. At present, conventional 2-D radiographic imaging and state-of-the-art 3-D cone-beam CT (CBCT) are typically employed for treatment verification. However, 2-D radiographic verification is mainly based on bony structures and/or implanted fiducials, and is sub-optimal for soft-tissue targets. While on-board CBCT can provide 3-D soft tissue information, it has three major limitations: 1) The acquisition time is limited to 60 seconds (~15 breathing cycles) for on-board CBCT, makes single breath- hold imaging impractical for organs which exhibit respiratory motion; 2) 360o mechanical clearance for CBCT acquisition may limit the use of CBCT for large patients, those with tumors at peripheral locations (e.g. breast), or those with substantial immobilization or support devices; 3) A high radiation dose (2-9 cGy) is delivered to the imaged volume with current imaging techniques, which is undesirable for daily imaging and may be a particular problem for those who are at high risk of developing second malignancies. To overcome these limitations, we propose an innovative digital tomosynthesis (DTS) imaging technology for 3-D target localization. Although DTS technology has been used for digital chest and mammography, its use in target localization is unknown. DTS only requires limited gantry rotation (e.g., a scan angle of 40o or less) to reconstruct 3-D anatomic information. Thus, imaging time and dose are substantially reduced compared to CBCT, making breath-hold DTS a simple solution for daily imaging of moving organs. Further, the reduced mechanical clearance needed for DTS makes it more widely applicable than CBCT. At present, the localization accuracy using DTS technology in treatment verification remains unknown. This proposal hypothesizes that the target localization accuracy using DTS technology is better than 2-D radiographs and is comparable to CBCT but with less imaging time and dose, and better mechanical clearance. To validate this hypothesis, Aim #1 is intended to determine optimal DTS scan angles for 4 anatomic sites: head and neck, thorax, abdomen, and pelvis. A small scan angle is desirable for imaging efficiency but less desirable for image quality. Therefore, we will assess the impact of scan angle on (a) the DTS contrast-to-noise ratio and resolution in phantoms and (b) the mutual information shared between DTS and CBCT slices, using patient data from the 4 anatomic sites. In Aim #2, we will then quantitatively compare DTS- based target localization accuracy to that of 2-D radiographs and CBCT using patient data from the 4 anatomic sites. To achieve this goal, three physicians will measure relative shifts and rotations between reference and on- board images using 2-D, DTS, CBCT technologies. We anticipate that the DTS target localization accuracy will be equivalent to CBCT and an improvement over 2-D radiographic imaging. Yet, we expect DTS to be more practical, more efficient, and deliver lower dose than full CBCT for daily 3-D target localization. Accurate alignment of the radiation-therapy beam with the tumor target is essential for removing the tumor and for sparing surrounding healthy tissue. Currently, on-board cone-beam CT (CBCT) is the best method for aligning soft-tissue tumor, such as tumor in the breasts, lungs, or lower abdomen, yet use of CBCT in target localization in radiation therapy is restricted by its long acquisition time, its demanding mechanical clearance requirements, and its high radiation dose. Some are difficult to improve because there is a limitation of gantry rotation speed for conventional linear accelerators. The digital tomosynthesis (DTS) approach that we propose will provide more widely and more routinely applicable alignment of soft tissue, via much shorter acquisition time, much less mechanical constraint, and much lower radiation dose. This more frequent and broader range of application will translate into more consistent elimination of tumor and into less damage to nearby healthy tissue.