Michał Spych, Leszek Gottwald, Małgorzata Klonowicz, Michał Biegała, Robert Bibik, Jacek Fijuth 60 Gy doses these differences, in mean total lung volumes, were respectively 13.51% vs. 7.64% and 8.64% vs. 4.02% in the groups of patients with and without clinical manifestation of post-radiation pneumonitis (p = 0.001; p < 0.003). Results of this analysis are presented in Table II. The analysis of the mean dose in the lung tissue defined as ipsilateral, contralateral and total lung volume showed a statistically significant difference in the case of total lung volume only. The mean dose which was absorbed in the total lung volume in the group of patients with post-radiation pneumonitis was 21.23 Gy, compared with 15.86 Gy in the group of patients without any signs of this acute side effect (p = 0.008). Neither high dose volumes in the ipsilateral lung, contralateral lung, mean ipsilateral and contralateral lung doses, nor PTVs or CTVs (cm3), showed a statistically significant difference in this patient population (p ≥ 0.07). The univariate analysis showed that the lung volumes receiving a dose of 10 Gy, ipsilateral lung and total lung volume receiving 20 Gy, and total lung volume receiving doses of 30 Gy and 40 Gy were correlated with the post-radiation pneumonitis risk. The multivariate analysis showed that only total lung volume receiving a dose of 10 Gy was correlated with the risk of post-radiation pneumonitis (p = 0.01). Results of the univariate and multivariate analysis are presented in Tables III and IV. Discussion The clinical manifestation of acute post-radiation toxicity of the lung tissue is the most frequently occurring side effect in patients with NSCLC after radical radiotherapy, which limits the possibility to deliver a high dose of ionizing radiation. The use of 3D-CRT with a growing number of therapeutic beams orientated to the patient in varied angles and positions causes better ability to spare normal lung tissue, but a great deal of lung volume absorbs low, scattered doses. In the present study we have attempted to identify clinical and dosimetric factors which can be responsible for clinical manifestation of lung injury in patients after radical radiotherapy. In the evaluated patient group acute post-radiation pneumonitis grade 2 had clinical manifestation in 15 (44.1%) patients, and 3 (8.9%) patients experienced grade 3 toxicity on the modified RTOG/EORTC scale. No grade 4 was recorded. The occurrence of grade 2 toxicity in this group of patients was not a significant clinical problem. We observed relatively rapid respiratory function amelioration after corticosteroid administration in these cases. Multiple reports based on RTOG/EORTC toxicity scores have described the percentage of grade 2 in the range of 7.8-36% [6, 10, 14, 15], and grade 3 in 2-14.3% of cases [6, 10, 15]. Inoue et al. reported toxicity of grade 1 and 2 in 36% of patients. Grade 3 and 4 toxicity was reported in 13% Table II. Student’s t test results for mean volumes of lung tissue which received doses in the range of 10-60 Gy Post RT (+) Post RT (–) V10 ipsilateral lung V10 contralateral lung V10 total lung V20 ipsilateral lung V20 contralateral lung V20 total lung V30 ipsilateral lung V30 contralateral lung V30 total lung V40 ipsilateral lung V40 contralateral lung V40 total lung V50 ipsilateral lung V50 contralateral lung V50 total lung V60 ipsilateral lung V60 contralateral lung V60 total lung 70.37389 46.04722 56.73556 58.16222 17.91167 36.14778 45.67556 7.86222 25.23111 35.66556 5.18278 19.28056 25.66556 2.96278 13.51056 16.91389 1.45611 8.64500 57.22625 31.44583 38.68500 47.66000 10.99417 20.41667 37.78500 6.64583 14.59667 30.15125 4.90333 11.36417 21.17125 2.97333 7.64083 12.22500 1.11083 4.02000 t 3.447838 3.636192 5.859693 2.913252 2.552560 5.410399 1.870949 0.852244 4.843179 1.428069 0.234055 4.204558 1.206850 –0.013575 3.623866 1.324020 0.733943 3.276891 df 24 28 28 24 28 28 24 28 28 24 28 28 24 28 28 24 28 28 p 0.002 0.001 < 0,001 0.007 0,016 < 0.001 0.074 0.401 < 0.001 0.166 0.816 < 0.001 0.239 0.989 0.001 0.198 0.469 < 0.003 Post RT (+) – patients with clinical manifestation of post-radiation pneumonitis, Post RT (–) – patients without any signs of side effects 760 Arch Med Sci 5, October / 2010