University College Hospitals NHS Foundation Trust, London, UK.
Radiother Oncol. 2010 Nov;97(2):189-93. doi: 10.1016/j.radonc.2010.04.025. Epub 2010 Jun 1.
This study investigated two fixed threshold methods to delineate the target volume using (18)FDG PET/CT before and during a course of radical radiotherapy in locally advanced squamous cell carcinoma of the head and neck.
Patients were enrolled into the study between March 2006 and May 2008. (18)FDG PET/CT scans were carried out 72h prior to the start of radiotherapy and then at 10, 44 and 66Gy. Functional volumes were delineated according to the SUV Cut Off (SUVCO) (2.5, 3.0, 3.5, and 4.0bwg/ml) and percentage of the SUVmax (30%, 35%, 40%, 45%, and 50%) thresholds. The background (18)FDG uptake and the SUVmax within the volumes were also assessed.
Primary and lymph node volumes for the eight patients significantly reduced with each increase in the delineation threshold (for example 2.5-3.0bwg/ml SUVCO) compared to the baseline threshold at each imaging point. There was a significant reduction in the volume (p⩽0.0001-0.01) after 36Gy compared to the 0Gy by the SUVCO method. There was a negative correlation between the SUVmax within the primary and lymph node volumes and delivered radiation dose (p⩽0.0001-0.011) but no difference in the SUV within the background reference region. The volumes delineated by the PTSUVmax method increased with the increase in the delivered radiation dose after 36Gy because the SUVmax within the region of interest used to define the edge of the volume was equal or less than the background (18)FDG uptake and the software was unable to effectively differentiate between tumour and background uptake.
The changes in the target volumes delineated by the SUVCO method were less susceptible to background (18)FDG uptake compared to those delineated by the PTSUVmax and may be more helpful in radiotherapy planning. The best method and threshold have still to be determined within institutions, both nationally and internationally.
本研究旨在探讨两种固定阈值方法，即在局部晚期头颈部鳞状细胞癌根治性放疗前后，利用（18）FDG PET/CT 勾画靶区。
2006 年 3 月至 2008 年 5 月期间，患者入组本研究。在放疗开始前 72 小时进行（18）FDG PET/CT 扫描，然后在 10、44 和 66Gy 时进行扫描。根据 SUV 截断值（SUVCO）（2.5、3.0、3.5 和 4.0bwg/ml）和 SUVmax 的百分比（30%、35%、40%、45%和 50%）阈值勾画功能体积。还评估了背景（18）FDG 摄取和体积内的 SUVmax。
与每个成像点的基线阈值相比，随着勾画阈值的增加（例如 2.5-3.0bwg/ml SUVCO），8 例患者的原发灶和淋巴结体积均显著减小。与 0Gy 相比，SUVCO 法在 36Gy 后体积显著减小（p⩽0.0001-0.01）。原发灶和淋巴结体积内的 SUVmax 与所给予的辐射剂量呈负相关（p⩽0.0001-0.011），但背景参考区的 SUV 无差异。由于用于定义体积边缘的感兴趣区域内的 SUVmax 等于或小于背景（18）FDG 摄取，并且软件无法有效区分肿瘤和背景摄取，因此，在 36Gy 后，PTSUVmax 法所勾画的体积随着所给予的辐射剂量的增加而增加。
与 PTSUVmax 法相比，SUVCO 法勾画的靶区体积变化较少受背景（18）FDG 摄取的影响，可能更有助于放疗计划。在国内外的机构内，仍需确定最佳方法和阈值。
