Left Breast Cancer Treated in Isocentric Lateral Decubitus (ILD) Position: An Alternative Technique Sparing Organs at Risk (OAR)

Abstract

Purpose : This study was designed to evaluate the doses delivered to two main organs at risk (OAR): the heart and left lung. Materials and Methods : Field design is as follows: the upper border is situated above the upper limit of the breast; the medial border is in the midline, adapted to the individual patient’s anatomy. The lateral (posterior) border is placed 1-2 cm beyond any palpable breast tissue. The inferior border is 1-2 cm below the inframammary fold. This field design allows the treatment of the whole breast, defined clinically by palpation plus a 1-2 cm margin. The isocenter is placed at mid-thickness of the flattened breast. For the medial field, the gantry is usually inclined up to 10°. A simulator computed tomography (CT) scan (Toshiba LB Aquilion) is used to perform localization films of both fields and several CT slices. The CT images are transferred to the Eclipse three-dimensional (3D) treatment planning system allowing graphic verification of the beam position. Using virtual simulation, two medial and lateral isocentric tangential beams with matching posterior borders are set up. In all patients, the breast volume, heart and lung were delineated and dose-volume histograms (DVH) were evaluated. Day-to-day reproducibility was easily verified by using the distance from the top of the treated breast to the corner of the epoxy disposer. Weekly portal imaging controls of both fields were performed in all patients. Individual dosimetric planning was performed with Eclipse V10 software (Varian) and a photon_AAA_100282 algorithm (calculated grid size: 0.25 cm). Results : From March 2012 to February 2013, fifty consecutive patients with early left breast cancer were studied: 33 received a total dose of 66 Gy dose /33 fractions (50 Gy to the breast and 16 Gy boost to the tumor bed), 17 pts received a dose of 41.6 Gy/13 fractions/ 5 weeks. In the 33 pts who received a total dose of 66 Gy, the heart received a mean dose of 1.71 Gy [1.28;2.69] . In the 17 pts who received a total dose of 41.6 Gy, the heart received a mean dose of 0.77 Gy [0.33;1.60]. In the 33 pts who received a total dose of 66 Gy, the lung received a mean dose of 0.97 Gy [0.57;1.61]. In the 17 pts who received a total dose of 41.6 Gy, the lung received a mean dose of 0.71 Gy [0.23;1.90]. Conclusions : Irradiation of the heart and lungs is extremely low in the lateral position using the 3D isocentric technique, despite the good coverage of the breast. This technique appears to be associated with a limited risk of heart and lung complications.