Comparison Of The Incidence Of Radiation Pneumonitis And Analysis Of Correlated Factors In Lung Cancer Treated By Intensity-modulated Radiotherapy Or Three-dimensional Conformal Radiotherapy

Objective: To observe the incidence of radiation pneumonitis(RP) with lung cancer treated by intensity-modulated radiotherapy(IMRT) or three-dimensional conformal radiotherapy(3D-CRT), and investigate the predictive value of clinical and DVH parameters on RP.Methods: 1 Comparison of the incidence of RP with lung cancer treated by IMRT or 3D-CRT and analysis of correlated factors of RP: A total of 85 patients with lung cancer treated by thoracic radiation therapy between July 2013 and July 2014 were prospectively enrolled. All patients were immobilized by thermoplast and scanned from lower neck to upper abdomen on the CT simulator. The tumor target and the organs at risk(OARs) were outlined. Involved nodal irradiation was adopted to the whole patients. GTV1 was including the primary tumor(GTV) and enlarged regional nodes(GTVn), CTV was defined to include the GTV plus a 6-8mm margin and the mediastinal lymph node regions, PTV as the CTV plus 5-8mm margin. Nine-five percent isodose line encompassed the PTV. The median prescribed doses for was 60Gy(range 50-64Gy), with 1.8-2.0Gy per fraction, five fractions per week. The acute RP was observed every week from the start of treatment to three months after the end of treatment and graded according to RTOG radiation scoring criteria. 2 To investigate the effect of different definitions for lung volume on the incidence of RP for lung cancer. 47 patients treated by IMRT were collected. The tumor targets were delineated. GTV was defined as the primary tumor, CTV as the GTV plus 6mm, PTV as the CTV plus 8mm. Normal lung volumes with different definitions were divided into four groups. Spearman correlative analysis was applied to study the effect of DVH parameters by different definitions on the incidence of RP.Results: 1 Thirty-three patients(38.82%) were observed with Grade 2 or higher RP and twelve patients(14.12%) with Grade 3 or higher RP. The onset time was at 45 days after radiotherapy. Univariate analysis showed that tumor location(P=0.030). smoking(P=0.024), MLD(P=0.037), V5-V25(P=0.005-0.038) and Vi5-Vi15(P=0.027-0.035) were risk factors for RP. Only smoking, V5, V8, V13 and V20 were found independently associated with Grade 2 or more RP in multivariate analysis. Spearman correlative analysis found that there was no correlation between the onset time of RP and clinical or DVH parameters. 2 The parameters varied considerably with different definitions of lung volume. V5 was a better predictor for RP in lung cancer treated by IMRT. The DVH parameters of the total lung volume minus GTV presented a better correlativity with RP.Conclusion: 1 There is no significant difference in the probability of RP, although IMRT may increase the low dose volume of the lung. 2 Tumor location, smoking, dosimetric parameters including MLD, V5-V25, and Vi5-Vi15 could predict RP. Smoking, V5, V8, V13, and V20 may be the most valuable predictors. Furthermore, V5 may be a better predictor for RP in patients treated by IMRT. 3 When the total lung volume minus GTV represented normal lung volume, the effect of DVH parameters on the incidence of RP would be better presented.