Dosimetric Comparision Of Three-dimensional Conformal Radiotherapy And Intensity-modulated Radiotherapy For Different Location Sites Of Lung Cancer

Objective To investigate dosimetry characteristic of using intensity-modulated radiation therapy (IMRT) compaired with three-dimensional conformal radiotherapy (3D-CRT) for different location sites of non-small cell lung cancer (NSCLC).Methods A retrospective treatment planning study was performed to compare intensity-modulated radiation therapy (IMRT) and conventional three-dimensional conformal radiation therapy (3D-CRT) for 10 NSCLC patients (Stage I~IIIB) in the upper lobes and 10 NSCLC patients (Stage I~IIIB) in the lower lobes. In the IMRT plans, five coplanar beams were designed. Step and shoot was used as our IMRT technique. Three to five coplanar beams were designed for 3D-CRT plans. The target included the primary tumor and regional nodes either≥1.0 cm in short-axis dimension on CT or standardized uptake values (SUVs)≥2.5 on PET. The goal was to deliver 66 Gy to >95% of the planning target volume (PTV) in 33 daily fractions while meeting multiple normal-tissue dose constraints. Heterogeneity correction was applied to all dose calculations (maximum allowable heterogeneity within PTV 20%). Nomal structure constraints were as follows: lung V20≤30%, mean lung dose≤15 Gy, esophagus V55≤30%, heart V40≤50% and the maximum dose to spinal cord could not exceed 45Gy. At the completion of all planning, analyzed PTV and OAR, including lung, esophagus, heart and spinal cord by using DVH.Then compaired respectively each parameter between 3D-CRT plans and IMRT ones of NSCLC in the upper lobes or in the lower lobes by using paired t-test or Wilcoxon signed-rank test, and compaired each parameter decrease between 3D-CRT plans and IMRT ones of NSCLC in the upper lobes to the corresponding ones in the lower lobes by using t-test or Wilcoxon rank sum test.Result①The indices of IMRT plans were superior to the 3D-CRT plans for NSCLC in the upper or lower lobes, the difference were statistically significant, including maximum dose to PTV (Dmax-PTV), mean dose to PTV (Dmean-PTV), dose distribution standard deviation (STD), conformity index (CI), hererogeneity index (HI), mean lung dose (MLD), lung parenchyma V10~V65 (in increments of 5Gy), V55 and mean dose of esophags, V40 of heart, acute and late esophageal complication probability.②Comparing to the 3D-CRT plans, the average V5 of lung were degraded about 2.7% ( p= 0.059) in the upper lobes, and 1.1% ( p= 0.721) in the lower lobes, the difference were not statistically significant.③Comparing the five-beams IMRT plans with the 3D-CRT plans for NSCLC in the upper lobes, the difference for V35 of esophagus and mean dsoe of heart were statistically significant, but for NSCLC in the lower lobes, the difference were not statistically significant.④Compaired the decrease V40 of heart between 3D-CRT plans and IMRT ones of NSCLC in the upper lobes to the corresponding ones in the lower lobes, the difference was statistically significant while the difference for other index were not statistically significant.Conclusions For NSCLC from the upper lobes or the lower lobes, the five-beam IMRT plans were more conformal than 3D-CRT plans, and significantly improved dose homogeneity within PTV compared with 3D-CRT. IMRT guarantees an important sparing of lungs, esophagus and heart, thus IMRT has the potential to improve therapeutic ratio, when compared with 3D-CRT, by means of dose escalation and/or combined treatment strategy; Applicating IMRT for the tumor located in the upper lobes seem superior to in the lower lobes. The dosimetric benefits of IMRT for non-small cell lung cancer should be evaluated further in clinical trials.