Michał Spych, Leszek Gottwald, Małgorzata Klonowicz, Michał Biegała, Robert Bibik, Jacek Fijuth Table IV. Multivariate analysis results V10 ipsilateral lung V10 contralateral lung V10 total lung V20 ipsilateral lung V20 total lung V30 total lung V40 total lung Beta 0.16870 0.65372 –3.03132 –0.97686 –0.02526 1.01562 –0.68254 Beta – coefficient, SD – standard deviation, HR – hazard ratio, W – Wald statistic SD 1.182774 0.654240 1.208014 1.308891 0.937207 1.702373 0.919531 HR 1.183765 1.922673 1.448252 0.376491 0.975052 2.761082 0.505331 W 0.020344 0.998401 6.296779 0.557003 0.100727 0.355923 0.550967 p 0.887 0.318 0.012 0.455 0.978 0.551 0.458 post-radiation lung toxicity. In univariate analysis the p values for these variables were 0.001 and 0.01 respectively. The multivariate analysis demonstrated that the lung volume which received the low dose of 20 Gy was the only prognostic factor for evaluation of the risk of acute post-radiation pneumonitis (p = 0.001). Additionally, the authors reported a direct statistical correlation between lung volume which received a dose of 20 Gy and acute lung toxicity intensification. There were no reported cases of acute post-radiation pneumonitis in the group of patients which received a dose of 20 Gy in less than 22% of total lung volume. For the range 22-31% of total lung volume which received the above-specified dose, the authors reported acute post-radiation pneumonitis of grade 2 according to the RTOG/EORTC toxicity score in 8% of patients. In the group of patients which received a dose of 20 Gy in total lung volume larger than 40%, the risk of serious incidents of acute post-radiation pneumonitis (grade 3-5 according to the RTOG/EORTC toxicity score) was 8%. Three patients died due to acute lung toxicity in this group of patients [10]. Similar results were reported by a group from Mayo Clinic. The authors reported a statistically significant relation between clinical manifestation of grade 2 acute post-radiation pneumonitis and the mean dose in the total lung volume. A statistically significant relation between total lung volume which received a dose equal to or higher than 10, 13, 15, 20 and 30 Gy, and grade 2 lung toxicity was reported in this study as well [8]. The group from M.D. Anderson Cancer Centre confirmed a thesis on particular sensitivity of lung tissue to low total and fractional doses of ionizing radiation. The range of low radiation doses absorbed in a large volume of lung tissue in patients treated for NSCLC, as well as mean dose in lung tissue, had an impact on clinical manifestation of post-radiation pneumonitis. Patients who received a dose of 5 Gy in total lung volume smaller than 42% had a lower risk of post- radiation lung toxicity compared to patients who received the same dose in a lung volume larger than 42% (p = 0.001) [12]. In the present study a statistical correlation between percentage total lung volume which received higher doses (40, 50 and 60 Gy) and the risk of clinical manifestation of post-radiation pneumonitis was demonstrated. This kind of correlation was not reported by authors from Washington University Medical Centre and Mayo Clinic [8]. This may result from differences in the definition of percentage total lung volume. The authors of those studies created total lung volume in the computer planning system excluding three volumes: GTV, CTV and PTV. In the present study ipsilateral and total lung volume were reduced by exclusion of CTV and PTV, but not GTV. Exclusion of these three volumes from the total lung volume could have a relatively large impact on the high dose distribution in lung tissue. The presented results as well as published data indicate that the risk of lung toxicity clinical manifestation is the most important factor which limits our ability to safely deliver a planned dose of ionizing radiation inside the thorax. In the course of treatment planning it is very important to pay special attention to low dose distribution in lung volume. Such a disadvantageous low dose distribution in lung tissue may result from using a large number of oblique therapeutic beams, which permit the delivery of nearly 100% of the planned dose to the PTV, but on the other hand significant lung tissue volume absorbs a low, dispersed dose of ionizing radiation. New treatment techniques of radiotherapy in patients with NSCLC are being evaluated to spare lung tissue and other organs and to reduce the toxicity risk [25, 26]. Additional studies are needed for a more robust description of the dose-volume effect following thoracic irradiation in lung cancer patients. In conclusions, in this analysis, the lung volume receiving a dose of 10 Gy is the most important dosimetric factor which influenced the post- radiation acute pneumonitis. Clinical manifestation of acute post-radiation pneumonitis revealed itself 762 Arch Med Sci 5, October / 2010