Low-dose and conventional-dose high resolution CT of pulmonary changes in breast cancer patients treated by tangential field radiotherapy.

Twenty-seven consecutive breast cancer patients receiving tangential field radiation therapy were followed by high resolution CT (HRCT) in order to compare the accuracy of reduced-dose HRCT and conventional-dose HRCT in the evaluation of subtle pulmonary changes. Thin section 1-mm HRCT images were obtained at identical levels at 120 kVp, with 320 mAs, 200 mAs, 160 mAs, 120 mAs and 60 mAs settings. HRCT was performed during the planning of radiotherapy and 4, 8 and 24 weeks after the completion of radiotherapy. Radiation was administered according to an individual CT-based plan by tangential fields with 4 or 6 MV photons to the whole breast given with 5 fractions of 1.9 Gy weekly to a total dose of 50 Gy. The tumor bed was boosted by electrons to 60 Gy. Pathological changes were detected in 21 examinations of 10 patients: 9 patients out of 27 (33%) showed radiation induced changes; 1 patient developed metastases within the irradiated volume. Septal thickening appeared in 5 patients at 4 weeks and in another 5 patients at 8 weeks. Parenchymal consolidation was detected in 1 patient at 4 weeks and in 5 patients at 8 weeks. HRCT using 160 mAs yield good quality images of subtle radiation induced injuries. The diagnostic validity of HRCT using lower than 160 mAs depends on the detail analyzed.