The aim of this study was to assess the frequency and the grade of RT-induced pulmonary fibrosis in patients who underwent EBRT compared to patients who underwent ELIOT. One-hundred-seventy-eight patients enrolled in a prospective randomized phase III trial to compare the efficacy of ELIOT (a single dose of 21 Gy prescribed at the 90% isodose) versus EBRT (50 Gy to the whole breast plus a 10 Gy boost to the tumour bed), underwent a spiral 16-detector row Computed Tomography (CT) examination to assess RT-induced pulmonary fibrosis: 83 patients in the EBRT arm and 95 in the ELIOT arm. All patients (age range 48-75 years) were affected by unicentric infiltrating carcinoma of the breast with diameter < 2.5 cm. This study was approved by our Institutional Ethical Committee and informed consent was obtained from each patient. Two observers, blinded to patient's randomization, independently evaluated each CT examination and assigned a fibrosis score (Grades 0 to 3). Inter-observer agreement for the fibrosis score was evaluated and a consensus between observers was obtained. Differences in fibrosis score between the two arms were evaluated by Chi Square test and Odds Ratio (OR) with 95% Confidence Intervals (CI). Pulmonary fibrosis was diagnosed in 42 patients (23.6%): 38 (90%) were in the EBRT arm and 4 (10%) in the ELIOT arm (p < 0.0001); twenty-six of them were Grade 1 (one ELIOT), fifteen were Grade 2 (three ELIOT) and one was Grade 3. The post-radiotherapy risk in the EBRT arm to develop at least Grade 1 fibrosis was 19 times higher than in the ELIOT one (OR: 19.20; 95%CI: 6.46-57.14) and 6 times higher to develop at least Grade 2 (OR: 5.70; 95%CI: 1.56-20.76). In conclusion, CT detected pulmonary fibrosis in patients treated with ELIOT is significantly less frequent compared to patients treated with EBRT.