The Irradiated Lung Volume in Tangential Fields for the Treatment of a Breast

Abstract

PURPOSE: Radiation pneumonitis is one of the complications caused by radiation therapy that includes a portion of the lung tissue. The severity of radiation induced pulmonary dysfunction depends on the irradiated lung volume, total dose, dose rate and underlying pulmonary function. It also depends on whether chemotherapy is done or not. The irradiated lung volume is the most important factor to predict the pulmonary dysfunction in breast cancer patients following radiation therapy. There are some data that show the irradiated lung volume measured from CT scans as a part of treatment planning with the tangential beams. But such data have not been reported in Korea. We planned to evaluate the irradiated lung volume quantitatively using CT scans for the breast tangential field and search for useful factors that could predict the irradiated lung volume. MATERIALS AND METHODS: The lung volume was measured for 25 patients with breast cancer irradiated with tangential field from Jan.1995 to Aug.1996. Parameters that can predict the irradiated lung volume included; (1) the perpendicular distance from the posterior tangential edge to the posterior part of the anterior chest wall at the center of the field (CLD); (2) the maximum perpendicular distance from the posterior tangential field edge to the posterior part of the anterior chest wall (MLD); (3) the greatest perpendicular distance from the posterior tangential edge to the posterior part of anterior chest wall on CT image at the center of the longitudinal field (GPD); (4) the length of the longitudinal field (L). The irradiated lung volume(RV), the entire both lung volume(EV) and the ipsilateral lung volume(IV) were measured using dose volume histogram. The relationship between the irradiated lung volume and predictors was evaluated by regression analysis. RESULTS: The RV is 61-279cc (mean 170cc), the RV/EV is 2.9-13.0% (mean 5.8%) and the RV/IV is 4.9-29.6% (mean 12.2%). The CLD, the MLD and the GPD are 1.9-3.3cm, 1.9-3.3cm and 1.4-3.1cm respectively. The significant relations between the irradiated lung volume such as RV, RV/EV, RV/IV and parameters such as CLD, MLD, GPD, L, CLDxL, MLDxL and GPDxL are not found with little variances in parameters. The RV/IV of the left breast irradiation is significantly larger than that of the right but the RV/EVs do not show the differences. There is no symptomatic radiation pneumonitis at least during 6 months follow up. CONCLUSION: The significant relationship between the irradiated lung volume and predictors is not found with little variation on parameters. The irradiated lung volume in the tangential field is less than 10% of entire lung volume when CLD is less than 3cm. The RV/IV of the left tangential field is larger than that of the right but there was no significant differences in RV/EVs. Symptomatic radiation pneumonitis has not occurred during minimum 6 months follow up.