Impact of Respiratory Maneuvers on Cardiac Volume Within Left-Breast Radiation Portals

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Abstract
Background Late cardiac morbidity and mortality have been reported among left-breast cancer survivors treated with radiation therapy. Radiation-induced cardiotoxicity is affected by the volume of myocardium included in the radiation portals. We hypothesize that simple respiratory maneuvers may alter the position of the heart relative to the portals without altering the radiation dose delivered to the breast. Methods and Results Fourteen healthy female adult volunteers underwent cardiac MRI to determine the cardiac volume included in the typical left-breast radiation field during respiratory maneuvers. Cardiac volume within the radiation portals was assessed from a transverse stack of 14 1-cm-thick contiguous slices covering the entire heart, obtained during breath holding at end-tidal volume (baseline), deep inspiration, and forced expiration. Thirteen subjects (92%) had inclusion of a portion of the heart within the radiation portals at end-tidal volume (median, 20.9 cm 3 ; range, 1.3 to 88.4 cm 3 ). In these subjects, inspiration decreased the cardiac volume included within the radiation portals (median change: −10.7 cm 3 [−40.2%], P <.001 versus end-tidal volume), whereas expiration increased the cardiac volume included (median change: 4.0 cm 3 [21.5%]; P <.001 versus end-tidal volume). Conclusions Inclusion of a portion of the heart in the left-breast radiation field is common. The use of simple inspiratory maneuvers significantly decreases cardiac volume within the radiation portals. Such an approach during delivery of radiation therapy may allow for preservation of radiation dosage to the breast while reducing cardiac involvement and subsequent mortality.