Prevention Of Radiation Pneumonitis In Breast Cancer Irradiation Through Dose-Volume Constraints.

693 Background: Previously, we have reported results on pulmonary side-effects in 481 irradiated women with breast cancer (BC). Moderate radiation pneumonitis (RP-G2) was diagnosed in 7–12 % of pat undergoing loco-regional RT. A mean reduction in vital capacity (VC) of 450 ml was found in the latter group. CT-changes correlated well with symptoms and VC-decline. The present study sought to determine whether dose-volume constraints, according to ROC-analysis from the previous study, would reduce the number of RP-G2 and the mean reduction in VC by half. We plan to accrue 120 pat undergoing loco-regional RT. Methods: The pat underwent 3-D dose planning aimed at minimizing the irradiated ipsilateral lung volume receiving > 20 Gy (V20) to < 30%. Pulmonary function testing was performed before and 5 mos. post-RT. Chest-CT was repeated 4 mos. post-RT and radiological changes compared to base-line were contoured and the mean doses in these sub-volumes were calculated. The patients were followed for signs of RP 1, 4 and 7 mos. post-RT. Data on potential confounding factors were collected prospectively, e.g. chemotherapy/tamoxifen exposure, smoking habits. Results: Among the first 50 pat. no case of RP-G2 and 3 cases of RP-G1 were diagnosed. No detectable VC-decline was found. The mean dose of the contoured CT sub-volumes with radiological changes was 39 Gy (range: 31–53). Conclusions: This preliminary analysis suggests that a V20 of < 30% is a safe dose volume level in postop RT for BC to avoid clinically significant RP and detectable VC-decline. Chest-CT could still detect RT-induced radiological changes in lung sub-volumes that received average doses in excess of 30 Gy. No significant financial relationships to disclose.