Early response of lung in breast cancer irradiation: radiologic density changes measured by CT and symptomatic radiation pneumonitis

Purpose: To quantify radiologic changes in the lung with CT after radiotherapy (RT) for breast cancer (BC) and to study their association with treatment techniques and symptomatic radiation pneumonitis (RP). Methods and Materials: CT scans of the lungs were performed before and 4 months after RT in 121 BC patients treated with four different RT techniques. The changes in mean density (MDCs) were analyzed at two lung levels (i.e., the central and apical CT slice). The central CT slice was also analyzed with respect to the MDCs in the anterior third and anterior half of the ipsilateral lung area. In mastectomized patients who received chest wall RT with an en-face electron beam, the maximal depths for a range of isodose curves were measured. The occurrence of mild/moderate symptomatic RP was assessed prospectively 1, 4, and 7 months after RT. Data on covariates with potential confounding effect on RT-induced lung toxicity were also collected prospectively. Results: In the entire study population, an association between the MDCs in the anterior third of the central CT slice and treatment technique (p<0.001) and symptomatic RP (p<0.001) was found. Among patients with chest wall treatment consisting of an en-face electron beam, the MDCs of the anterior third of the central CT slice correlated with the 35% isodose curve (16-30 Gy) (p=0.046) and age (p<0.001). No association between post-RT lung density changes and pre-RT chemotherapy, concurrent tamoxifen intake, or smoking habits was found. Among patients treated with locoregional RT, an association was found between the MDCs in the anterior third of the central CT slice and the incidence of RP. MDCs in the apical CT slice, however, were not associated with RP. Conclusion: The results imply that short-term post-RT lung density changes and symptomatic RP were associated with RT techniques, total doses as low as 16-30 Gy, and increasing age. Structural changes in the central part of lung appeared to be more important for the development of RP than changes in the apex