Is there an impact of heart exposure on the incidence of radiation pneumonitis? Analysis of data from a large clinical cohort
Background. The goal of the present study was to determine, in a large clinical cohort, whether incidental radiation exposure to the heart during definitive radiotherapy of inoperable non-small cell lung cancer (NSCLC) detectably increased the risk of radiation pneumonitis (RP) beyond that resulting from radiation exposure to lung. Material and methods. Data were analyzed from all patients who received definitive three-dimensional (3D) concurrent radiotherapy or intensity-modulated radiotherapy for the treatment of NSCLC over a 10-year period at our institution, except those who had previous lung cancer or for whom radiation treatment plans were unavailable for calculation of heart and lung dose-volume histograms (DVHs). Parameters computed from heart and lung DVHs included mean lung dose (MLD), effective lung dose computed using volume parameter n = 0.5 (Deff), mean heart dose (MHD), percentage of heart receiving > 65 Gy (V65), and minimum dose to the hottest 10% of heart (D10). Univariate and multivariate normal-tissue complication probability (NTCP) models were used to analyze incidence of Grade ≥ 2 or Grade ≥ 3 RP as a function of these and other parameters. Results. The study cohort included 629 patients, with crude rates of Grade ≥ 2 RP and Grade ≥ 3 RP of N = 263 (42%) and N = 124 (20%), respectively. Univariate NTCP models based on dosimetric lung parameters (MLD and Deff) fit the data better than models based on univariate heart parameters (heart D10, heart V65 or MHD). In multivariate modeling, incorporation of heart parameters did not significantly improve the fit of RP risk models based on lung parameters alone (p > 0.38 in each case). Conclusions. In this large clinical cohort, there was no evidence that incidental heart exposure during radiotherapy of NSCLC had a detectable impact on the occurrence of moderate or severe RP.