An Improved Internal Mammary Irradiation Technique in Treatment of Locally Advanced Breast Cancers

Abstract

Purpose: To improve sparing of ipsilateral lung and heart and reduce the ?cold? and ?hot? spots in breast tissue for irradiation of internal mammary nodes in locally advanced breast cancers.
Materials and Methods: A modified internal mammary irradiation technique is proposed. It uses wide tangential fields for the first 8 fractions of treatment. A medial internal mammary field (IMF) of electrons matched with narrowed tangential fields is used for the remaining fractions. Intensity Modulated Radiation Therapy (IMRT) by means of segmented multi-leaf collimation (SMLC) is used in the narrowed tangential fields to improve the match between the electron and the photon fields. Treatment planning is performed to compare this technique to a wide-tangential-only technique and to a traditional oblique IMF technique for three patients with differing habitus. Film dosimetry is performed in solid water phantom to confirm the planning results.
Results: For all three patients, the mean doses of the ipsilateral lung and the heart are significantly reduced with the modified technique. The lung and the heart volumes are remarkably reduced at low dose levels (