Importance of dosimetric factors predicting radiation toxicity in lung cancer treatment

To evaluate prognostic importance of dosimetric parameters (V20, V30 and V40) in the incidence of lung radiation toxicity caused by external-beam radiation therapy in patients with lung cancer. A total of 82 patients with lung cancer were analyzed prospectively. They were treated in the Oncology Institute of Vilnius University from 2002 to 2005. Three-dimensional conformal radiotherapy was administered to all patients; radiation dose was > or =50 Gy, delivered in daily fractions of 2 Gy. All patients received concurrent chemotherapy and part of them - surgery. All patients were evaluated before radiation therapy and after 3-, 6-, and 12-month follow-up. V20, V30, and V40 were calculated from dose-volume histograms using the Eclipse(TM) radiotherapy treatment planing system. Based on radiological findings and clinical symptoms radiation-induced lung injury (radiation pneumonitis and radiation fibrosis) was diagnosed. Nearly half of patients (48%) developed grade < or =2 pulmonary toxicity according to the Subjective, Objective, Management and Analytic/Late Effects on Normal Tissues (SOMA/LENT) scale. The percentage volume of normal lung tissue receiving >20 Gy dose was 38%, >30 Gy--25%, and >40 Gy--18%. In patients free of radiation toxicity V20 was 30%, V30--22%, and V40--18%, and in patients with radiation-induced pulmonary toxicity V20 was 48%, V30--30%, and V40--18%. Dosimetric parameters V20, V30, and V40 are significant predictive factors for radiation-induced pulmonary toxicity. At this time planned V20 and V30 are too high and they should be minimized in order to reduce radiation-induced pulmonary toxicity.