Since 2001, 50 breast cancer patients, for whom extensive lung/heart involvement was expected from the use of conventional tangential 2-field technique (2F) owing to complex anatomies, were irradiated using a 3-field conformal technique (3F). Dose plans were designed for both 3F and 2F and a dose volume histogram analysis on ipsilateral lung, heart, and target was conducted. The 3F technique allowed a significant reduction in ipsilateral lung irradiation: mean dose dropped from 16.0+/-3.8 (2F) to 12.0+/-2.7 Gy (3F) and V(45Gy) from 20.7+/-6.8 (2F) to 3.2+/-2.9% (3F). Similarly, in patients irradiated to the left breast, heart mean dose was reduced from 8.1 Gy (2F) to 6.8 Gy (3F) and D(15%) from 19.0 Gy to 14.0 Gy. All differences reached a high degree of significance. The target coverage was not clinically compromised since the slight reduction using 3F compared with 2F is limited to V(95%) while V(90%) difference, even if statistically significant, is small: 98.2+/-1.8% (3F) and 98.8+/-1.6 (2F). A preliminary report on clinical follow up is also included; with a mean follow up of 15.8 months, no pulmonary or cardiac complications were observed.