Heart and lung sparing with isocentric lateral decubitus positioning compared with dorsal decubitus positioning during adjuvant localized breast cancer radiotherapy.

Abstract

Objectives: The cardiac and pulmonary dosimetric benefit of alternative positioning in isocentric lateral decubitus compared with dorsal decubitus during adjuvant breast irradiation has yet to be proven, in spite of the relative long-standing use of isocentric lateral decubitus.

Methods: Eight consecutive patients with an indication for adjuvant breast irradiation without boost or lymph node irradiation were scanned in both isocentric lateral and dorsal decubitus positions. For each patient, a plan delivering 40.05 Gy in 15 fractions in isocentric lateral decubitus and in dorsal decubitus using a field-in-field technique were calculated. Doses to the heart, to various cardiac substructures and to the lungs were compared.

Results: Mean dose to the heart, to various cardiac structures (left ventricle, left coronary, right coronary), to the homolateral lung and to the contralateral lung were significantly lower in isocentric lateral decubitus than in dorsal decubitus. Average absolute mean dose reductions were -40 cGy for the heart, -27.5 cGy for the left ventricle, -56.5 cGy for the right coronary artery, -64.5 cGy for the left coronary artery, -45.5 cGy for the sino-atrial node, -74 cGy for the homolateral lung and -4.5 cGy for the contralateral lung. For all organs-at-risk, median dose-volume histograms in isocentric lateral decubitus showed lower relative volumes than in dorsal decubitus.

Conclusion: lateral decubitus positioning significantly reduces dose to the heart, to various cardiac substructures, to the homolateral lung and to the contralateral lung, compared with dorsal decubitus.This technique is easily implemented and can be widely recommended to reduce heart and lung doses to a minimum.