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 f ield radiation therapy were followed by high resolution CT (HRCT) in o rder to compare the accuracy of reduced-dose HRCT and conventional-dos e HRCT in the evaluation of subtle pulmonary changes. Thin section l-m m HRCT images were obtained at identical levels at 120 kVp, with 320 m As, 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 co mpletion of radiotherapy. Radiation was administered according to an i ndividual 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 d ose of 50 Gy. The tumor bed was boosted by electrons to 60 Gy. Patholo gical changes were detected in 21 examinations of 10 patients: 9 patie nts out of 27 (33%) showed radiation induced changes; 1 patient develo ped metastases within the irradiated volume. Septal thickening appeare d in 5 patients at 4 weeks and in another 5 patients at 8 weeks. Paren chymal consolidation was detected in 1 patient at 4 weeks and in 5 pat ients at 8 weeks. HRCT using 160 mAs yield good quality images of subt le radiation induced injuries. The diagnostic validity of HRCT using l ower than 160 mAs depends on the detail analyzed.