Analysis Of CT Values And Dosimetric Factors Influencing Radiation-induced Pneumonitis

ObjectiveThis study aimed to identify the CT values and dosimetric parameters related to the risk of radiation-induced pneumonitis?RP?after definitive radiotherapy in Patients with thoracic radiotherapy.Materials and MethodsA total of 164 lung and esophagus cancer patients who received thoracic radiotherapy were retrospectively recruited.Where baseline CT values considered were 5–50 Gy in increments of 5Gy on CT images.Ten lung subsets were auto-segmented in the bilateral lung of the planning CT(HU₅ represents average CT values of lung between 0-5Gy,HU₁₀represents average CT values of lung between 5-10Gy,HU₁₅5 represents average CT values of lung between 10-15Gy,HU₂₀0 represents average CT values of lung between 15-20Gy),the rest can be done in the same manner(HU₂₅?HU₃₀?HU₃₅?HU₄₀?HU₄₅?HU₅₀).And for whom dosimetric parameters were available from the DVH.The severity of RP was graded using Common Toxicity Criteria for Adverse Events,version 4.0?CTCAE4?.Logistic regression was performed for multivariate analysis of RP using a backward regression procedure including the general situation?dosimetric factors and CTvalues with a P-value<0.05 in the univariate analysis.Receiver-operating characteristic?ROC?curves were generated to define the cutoff value.Result26.2%?43/164?of patients progressed to?grade 2 RP?grade 2:n=42,25.6%;grade 3:n=1,0.6%?,while only 17.5%?10/57?of esophageal patients.One patient fevered and developed RP during radiotherapy,so ended the radiation.Only the baseline HU₁₀ were associated with RP.Smoking was obviously relevant to RP.V5?V20?V30?MLD were found to be significantly associated with RP.For the multivariate analysis,MLD was identified as an independent risk factor for RP.The cutoff values of MLD as calculated by the ROC curves was 14.3Gy The incidence of RP was35.5%,8.6%if MLD was>14.3Gy and?14.3Gy.The sensitivity and specificity were separately 0.88?0.57.Conclusion1.The Baseline CT values of RP tend to be higher,but Still needs a large number of prospective studies;2.V₅?V₂₀?V₃₀ and MLD were related to RP;3.MLD was to be an independent predictive factor for RP.