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背景与目的:放疗过程中,肿瘤退缩会造成其空间位置改变,进而可能影响肿瘤内放疗剂量分布。本研究探讨NSCLC放疗过程中肿瘤退缩对计划靶体积(PTV)和肿瘤周围关键器官剂量分布的影响。方法:选择从2003年1月—2005年12月,在我院接受根治性放疗的NSCLC患者10例。所有患者均行定位CT扫描,制定三维适形放疗计划,在放疗开始约4周后,大体肿瘤体积(GTV)剂量达到40~50Gy时,行第2次定位CT扫描,两次定位CT扫描,患者采用相同固定装置、保持相同体位。回顾性分析这些患者的定位CT:根据首次定位CT制定三维适形放疗计划Plan1,处方剂量为64Gy/32次;根据第2次定位CT制定的三维适形放疗计划Plan2,处方剂量为24Gy/12次;将Plan1的处方剂量更改为40Gy/20次,之后与Plan2叠加,形成计划Plan3,Plan3用于模拟开始放疗时采用Plan1,当GTV剂量达40Gy后,采用根据退缩后肿瘤制定的放疗计划Plan2完成治疗。比较两次定位CT上GTV的体积;以D95(95%PTV体积接受的剂量)、D99和V100%(接受处方剂量的PTV体积所占的百分比)为参数,比较采用Plan1时,PTV1(根据首次定位CT确定的计划靶体积)和PTV2(根据第2次定位CT确定的计划靶体积)的剂量分布差异;以双肺(减去PTV的体积)接受大于20Gy照射的体积(V20)、平均剂量(MLD),脊髓的最大剂量(Dmax)、1cm3脊髓受到的剂量(D1cm3),心脏的平均剂量(MHD),食管接受大于55Gy照射的体积(V55)、平均剂量(MED)为参数,比较采用Plan1与采用Plan3时肿瘤周围关键器官的剂量分布差异。资料采用配对t检验。结果:GTV剂量达到39.6~52.5Gy后,GTV体积绝对缩小量的中位值为:9.5cm3(1.7~64.4cm3),GTV体积相对缩小量的中位值为:22.35%(10.05%~54.81%),与放疗前相比,GTV的体积差异具有显著性(P=0.015)。采用Plan1,PTV1与PTV2的剂量分布差异无显著性。Plan1与Plan3相比,正常肺组织、脊髓和食管的剂量分布差异无显著性;心脏接受的剂量在采用Plan3时减小(P=0.023)。结论:NSCLC放疗过程中肿瘤退缩对PTV剂量分布未产生具有统计学显著性的影响,但是,根据退缩后的肿瘤重新制定放疗计划可以减少肿瘤周围关键器官接受的剂量,尤其是可以减少心脏接受的剂量。
BACKGROUND & OBJECTIVE: During the course of radiotherapy, the shrinkage of the tumor will cause the change of its spatial position, which may in turn affect the dose distribution of the radiotherapy in the tumor. This study was to investigate the effect of tumor regression on planned target volume (PTV) and the dose distribution of key organs around NSCLC during radiotherapy. Methods: Ten patients with NSCLC undergoing radical radiotherapy in our hospital from January 2003 to December 2005 were selected. All patients underwent positioning CT scan to establish a three-dimensional conformal radiotherapy plan. After about 4 weeks of radiotherapy, when the gross tumor volume (GTV) dose reached 40-50 Gy, the second positioning CT scan and CT scan were performed twice. Patients using the same fixation device, to maintain the same position. A retrospective analysis of the location of these patients CT: according to the first positioning CT to develop three-dimensional conformal radiotherapy plan Plan1, the prescribed dose of 64Gy / 32 times; according to the second positioning CT developed three-dimensional conformal radiotherapy plan Plan2, prescription dose of 24Gy / 12 Times; the prescription dose of Plan1 was changed to 40 Gy / 20 times, and then overlaid with Plan2 to form Plan3; Plan3 was used to simulate Plan1 when radiotherapy was started. When GTV dose reached 40 Gy, radiotherapy plan Plan2 Complete the treatment. The volumes of GTV on CT were compared twice. The D95 (95% PTV volume received), D99 and V100% (PTV volume of the prescribed dose) were used as parameters to compare the effect of Planl on PTV1 (Target volume determined by positioning CT) and PTV2 (planned target volume determined by positioning second CT); volume (V20) of greater than 20 Gy irradiated with both lungs (volume minus PTV), average dose (MLD), maximum spinal cord (Dmax), 1cm3 spinal cord (D1cm3), cardiac average (MHD), esophageal volume greater than 55Gy (V55) and average dose (MED) Differences in dose distribution between Plan1 and the key organs around the tumor using Plan3. Data using paired t test. Results: After the GTV dose reached 39.6-52.5Gy, the median value of GTV volume reduction was 9.5cm3 (1.7-64.4cm3). The median volume of GTV volume reduction was 22.35% (10.05% -54.81% ), The volume difference of GTV was significant compared with that before radiotherapy (P = 0.015). There was no significant difference in the dose distribution between Plan1, PTV1 and PTV2. There was no significant difference in the dose distribution between Plan1 and Plan3 in normal lung, spinal cord and esophagus. Cardiac accepted dose decreased with Plan3 (P = 0.023). CONCLUSIONS: Tumor regression during NSCLC radiotherapy did not have a statistically significant effect on the PTV dose distribution, but re-engineering radiation regimens based on tumor regression can reduce the dose received by key organs surrounding the tumor and, in particular, reduce cardiac acceptance dose.