Dosimetric Advantages of the Field-in-field Plan Compared with the Tangential Wedged Beams Plan for Whole-breast Irradiation

Abstract

The purpose of this study is to evaluate the dosimetric outcome of the field-in-field (FIF) plans compared with tangential wedged beams (TWB) plans for whole breast irradiation of breast cancer patients. Twenty patients with right-sided breast cancer and 10 patients with left-sided breast cancer were retrospectively enrolled in this study. We generated a FIF plan and a TWB plan for each patient to compare dosimetric outcomes. The dose the homogeneity index (HI), the conformity index (CI) and the uniformity index (UI) were defined and used for comparison of the dosimetric outcome of the planning target volume (PTV). To compare the dosimetric outcome of the organs at risk, the mean dose (D mean) and the percentage of volumes receiving more than 10, 20 and 30 Gy of the ipsilateral lung and heart were used. The FIF plans had significantly lower HI (p=0.002), higher UI (p=0.000) and CI (p=0.000) than those of the TWB plans, which means that the FIF plans were better than the TWB plans in the dosimetric comparisons of the PTV. The V10 lung (17.1±7.1 vs. 18.6±6.6%, p=0.020) and V30lung (10.3±5.1% vs. 10.7±5.2%, p=0.000) were lower with the FIF plans compared with those of the TWB plans, with statistical significance. For the left-sided breast cancer patients, Dmean of the heart (2.6±1.3 vs. 3.2±1.4 Gy, p=0.000), V20heart (3.4±2.6 vs. 3.6±2.8%, p=0.005) and V30heart (2.6±2.3% vs. 2.9±2.4%, p=0.004) were significantly lower for the FIF plans in comparison with those of the TWB plans. The FIF plans increased the dose homogeneity, conformity and uniformity of the target volume for the whole-breast irradiation compared with the TWB plans. Moreover, FIF plans reduced the doses to the ipsilateral lung and heart.