Breast Dosimetry: A Phantom study between tangential wedge fields and multiple open field-in-field 3D conformal forward planning

Abstract

Whole breast irradiation frequently leads to acute and long term toxicities which many studies [1-3] has shown to be associated with dose inhomogeneity (hot spots). A 3D conformal forward planning technique was studied to improve dose uniformity and potentially reduce toxicity for breast irradiation using segmented field-in field (FIF). A Rando Alderson female anthropomorphic phantom was CT scanned, planned with two conventional tangential wedge fields and then planned with the FIF technique. A 3D dose distribution for the tangential wedge fields (i.e. motorized wedges on the medial and lateral tangential) were obtained by selecting the best possible wedge combinations and photon energies, with the goal of reducing the hot spots in the breast below 110 percent of the prescribed dose. The 3D conformal forward plan employed using the multiple FIF was to achieve an optimal dose distribution and desired homogeneity through a complex manual fluence map optimization process. The FIF plan resulted in smaller “hot spots” far below 110% with a maximum dose of 102.8%, while maintaining greater coverage of the treatment volume. The dose homogeneity index was 1.00 of the treatment volume when using FIF as compared to 1.03 with standard wedges. The use of 3D forward planning with FIF technique for tangential breast radiotherapy is an efficient and effective method for achieving uniform dose throughout the breast. It is dosimetrically superior to the treatment technique that employs only wedges.