Lavrenkov Konstantin, Christian Judith A, Partridge Mike, Niotsikou Elena, Cook Gary, Parker Michelle, Bedford James L, Brada Michael
Lung Research Unit, The Royal Marsden NHS Foundation Trust, The Institute of Cancer Research, Surrey, UK.
Radiother Oncol. 2007 May;83(2):156-62. doi: 10.1016/j.radonc.2007.04.005. Epub 2007 May 9.
The study aimed to examine specific avoidance of functional lung (FL) defined by a single photon emission computerized tomography (SPECT) lung perfusion scan, using intensity modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3-DCRT) in patients with non-small cell lung cancer (NSCLC).
Patients with NSCLC underwent planning computerized tomography (CT) and lung perfusion SPECT scan in the treatment position using fiducial markers to allow co-registration in the treatment planning system. Radiotherapy (RT) volumes were delineated on the CT scan. FL was defined using co-registered SPECT images. Two inverse coplanar RT plans were generated for each patient: 4-field 3-DCRT and 5-field step-and-shoot IMRT. 3-DCRT plans were created using automated AutoPlan optimisation software, and IMRT plans were generated employing Pinnacle(3) treatment planning system (Philips Radiation Oncology Systems). All plans were prescribed to 64 Gy in 32 fractions using data for the 6 MV beam from an Elekta linear accelerator. The objectives for both plans were to minimize the volume of FL irradiated to 20 Gy (fV(20)) and dose variation within the planning target volume (PTV). A spinal cord dose was constrained to 46 Gy. Volume of PTV receiving 90% of the prescribed dose (PTV(90)), fV(20), and functional mean lung dose (fMLD) were recorded. The PTV(90)/fV(20) ratio was used to account for variations in both measures, where a higher value represented a better plan.
Thirty-four RT plans of 17 patients with stage I-IIIB NSCLC suitable for radical RT were analysed. In 6 patients with stage I-II disease there was no improvement in PTV(90), fV(20), PTV/fV(20) ratio and fMLD using IMRT compared to 3-DCRT. In 11 patients with stage IIIA-B disease, the PTV was equally well covered with IMRT and 3-DCRT plans, with IMRT producing better PTV(90)/fV(20) ratio (mean ratio - 7.2 vs. 5.3, respectively, p=0.001) and reduced fMLD figures compared to 3-DCRT (mean value - 11.5 vs. 14.3 Gy, p=0.001). This was due to reduction in fV(20) while maintaining PTV coverage.
The use of IMRT compared to 3-DCRT improves the avoidance of FL defined by perfusion SPECT scan in selected patients with locally advanced NSCLC. If the dose to FL is shown to be the primary determinant of lung toxicity, IMRT would allow for effective dose escalation by specific avoidance of FL.
本研究旨在探讨在非小细胞肺癌（NSCLC）患者中，使用调强放射治疗（IMRT）和三维适形放射治疗（3-DCRT）时，通过单光子发射计算机断层扫描（SPECT）肺灌注扫描定义的功能性肺（FL）的特定回避情况。
NSCLC患者在治疗体位接受计划计算机断层扫描（CT）和肺灌注SPECT扫描，使用基准标记以便在治疗计划系统中进行配准。在CT扫描上勾画放射治疗（RT）靶区。使用配准后的SPECT图像定义FL。为每位患者生成两个反向共面RT计划：4野3-DCRT和5野步进式IMRT。3-DCRT计划使用自动AutoPlan优化软件创建，IMRT计划使用Pinnacle(3)治疗计划系统（飞利浦放射肿瘤系统）生成。所有计划均使用Elekta直线加速器6 MV射线的数据，处方剂量为64 Gy，分32次给予。两个计划的目标都是将照射到20 Gy的FL体积（fV(20)）和计划靶区（PTV）内的剂量变化降至最低。脊髓剂量限制在46 Gy。记录接受90%处方剂量的PTV体积（PTV(90)）、fV(20)和功能性平均肺剂量（fMLD）。PTV(90)/fV(20)比值用于考虑两种测量值的变化，该比值越高表示计划越好。
分析了17例适合根治性RT的I-IIIB期NSCLC患者的34个RT计划。在6例I-II期患者中，与3-DCRT相比，使用IMRT时PTV(90)、fV(20)、PTV/fV(20)比值和fMLD均无改善。在11例IIIA-B期患者中，IMRT和3-DCRT计划对PTV的覆盖效果相当，但IMRT产生的PTV(90)/fV(20)比值更好（平均比值分别为7.2和5.3，p = 0.001），与3-DCRT相比fMLD数值降低（平均值分别为11.5和14.3 Gy，p = 0.001）。这是由于在保持PTV覆盖的同时fV(20)降低。
与3-DCRT相比，IMRT的使用可改善局部晚期NSCLC特定患者中由灌注SPECT扫描定义的FL的回避情况。如果显示FL剂量是肺毒性的主要决定因素，IMRT将通过特定回避FL实现有效的剂量递增。
