Vancouver Cancer Centre, Vancouver, BC, Canada.
Int J Radiat Oncol Biol Phys. 2010 Oct 1;78(2):587-94. doi: 10.1016/j.ijrobp.2009.11.035. Epub 2010 May 6.
To assess the impact of attenuation and scatter corrections on the calculation of single photon emission computed tomography (SPECT)-weighted mean dose (SWMD) and functional volume segmentation as applied to radiation therapy treatment planning for lung cancer.
Nine patients with lung cancer underwent a SPECT lung perfusion scan. For each scan, four image sets were reconstructed using the ordered subsets expectation maximization method with attenuation and scatter corrections ranging from none to a most comprehensive combination of attenuation corrections and direct scatter modeling. Functional volumes were segmented in each reconstructed image using 10%, 20%, …, 90% of maximum SPECT intensity as a threshold. Systematic effects of SPECT reconstruction methods on treatment planning using functional volume were studied by calculating size and spatial agreements of functional volumes, and V(20) for functional volume from actual treatment plans. The SWMD was calculated for radiation beams with a variety of possible gantry angles and field sizes.
Functional volume segmentation is sensitive to the particular method of SPECT reconstruction used. Large variations in functional volumes, as high as >50%, were observed in SPECT images reconstructed with different attenuation/scatter corrections. However, SWMD was less sensitive to the type of scatter corrections. SWMD was consistent within 2% for all reconstructions as long as computed tomography-based attenuation correction was used.
When using perfusion SPECT images during treatment planning optimization/evaluation, the SWMD may be the preferred figure of merit, as it is less affected by reconstruction technique, compared with threshold-based functional volume segmentation.
评估衰减和散射校正对单光子发射计算机断层扫描（SPECT）加权平均剂量（SWMD）计算和功能体积分割的影响，这些影响应用于肺癌放射治疗计划。
9 名肺癌患者接受了 SPECT 肺灌注扫描。对于每次扫描，使用有序子集期望最大化方法重建了四组图像，其中包括从无衰减和散射校正到最全面的衰减校正和直接散射建模组合的校正。在每个重建图像中，使用 10%、20%、……、90%的最大 SPECT 强度作为阈值对功能体积进行分割。通过计算功能体积的大小和空间一致性，以及实际治疗计划中的功能体积 V(20)，研究了 SPECT 重建方法对使用功能体积的治疗计划的系统影响。为各种可能的机架角度和射野大小的射线计算了 SWMD。
功能体积分割对 SPECT 重建使用的特定方法敏感。在使用不同衰减/散射校正的 SPECT 图像重建中，观察到功能体积的变化高达>50%。然而，SWMD 对散射校正的类型不太敏感。只要使用基于计算机断层扫描的衰减校正，所有重建的 SWMD 都在 2%以内保持一致。
在治疗计划优化/评估期间使用灌注 SPECT 图像时，SWMD 可能是首选的评估指标，因为与基于阈值的功能体积分割相比，它受重建技术的影响较小。
