PET对非小细胞肺癌三维适形放疗计划的影响

Impact of positron emission tomography on 3-dimensional conformal radiation therapy planning of non-small cell lung cancer

正电子发射计算机断层显像(positron emission tomography, PET)作为一种先进的功能影像技术,通过影响非小细胞肺癌(non-small cell lung cancer, NSCLC)的临床分期,而影响其三维适形放疗(3-dimensional conformal radiation therapy, 3D-CRT)计划的制定与实施.对于伴阻塞性肺炎、肺不张、胸膜受侵和胸腔积液者,CT确定肿瘤边界有一定困难,但PET却能较好地鉴别肿瘤组织与正常组织,因而能更精确地进行T分期并可明显缩小照射野,减少正常组织受量;对于受呼吸运动、心脏搏动影响较大的肿瘤,PET能提供精确的三维模拟图象,从而能据以制定出个体化的放疗计划.PET检测纵隔淋巴结的敏感性比CT高,对直径≤1 cm的淋巴结的检出率尤其高,从而可发现CT阴性的转移淋巴结,也可排除CT阳性的正常淋巴结而修正常规的N分期.PET诊断远处转移的优势也比其他影像学手段明显,尤其对Ⅲ期患者更为有益.PET可改变20%～30% NSCLC患者的整体治疗策略,使不同的靶区勾画者之间的差异性明显减小,趋同性明显增大.PET可减少对周围正常组织的放射性肺损伤,更严格地执行根治性放疗的指征,降低与放疗有关的死亡率而大大增加治疗收益.但图象融合方式的选择、靶区运动的控制、结果判断标准的选取仍是未来研究的重要课题.

As an advanced functional imaging, through influencing clinical staging of non-small cell lung cancer, positron emission tomography (PET) has an important impact on the establishment and implement of its 3-dimensional conformal radiation therapy planning. In patients with atelectasis, obstructive pneunonitis, pleural effusion, and thoracic extravasate, target volume definition with CT is somewhat difficult. However, PET can distinguish tumor tissue from normal tissue and so can help to undergo T stage more accurately. PET can reduce irradiated volume significantly and so unnecessary irradiation of normal tissue can be avoided. For tumors affected much by respiratory movement and heartbeat, PET can offer more accurate 3-dimensional simulative image than CT and can perform individual radiation treatment planning. The sensitivity of PET in detecting mediastinal lymph node is higher than CT, especially for that whose diameter is equal or larger than 1 cm. So PET can detect involved lymph node that is negative on CT while can confirm normal lymph node that is positive on CT. Therefore, PET can modify conventional N stage. PET has more distinct predominance in diagnosing metastasis than other imaging approaches, especially for those who are Staged Ⅲ conventionally. PET can change their overall treatment strategy in about 20%-30% patients. Interobserver variation can be decreased notably and compromise among the observers may be obtained more easily. PET can decrease radiation pulmonary toxicity, perform radical radiation planning more strictly, and reduce death rate caused by radiotherapy, and so can enhance treatment income distinctly. However selection of image fusion manner, control of target motion, and choice of judging criterion are still significant issues to be studied in the future.