Target Volume Definition and Target Conformal Irradiation Technique for Breast Cancer Patients

Abstract

The aim of this study was to present the target volume and irradiation technique in the most complex situation where the breast or chest wall and the locoregional lymphatics (mammaria interna lymph nodes, axillary and supraclavicular lymph nodes) have to be irradiated. The study comprised 125 breast cancer patients treated with curative intent after primary surgery in the last two years at our institute. In 62 cases the target volume included the breast or chest wall and the locoregional lymphatics, which were treated using our irradiation technique. The target conformal irradiation technique is a multiple non-opposed beams one isocenter technique developed to protect the heart and lungs. This technique, consisting of several rotation beams modulated with wedge filters and individual lung absorbers as well as additional fixed beams, was used in our study to apply a homogeneous dose of 46 to 56 Gy to the target volume; the irradiation technique was optimized by means of dose-volume histograms. After pre-localization, the patients underwent computerized tomographic scanning, with sections at 1.0 cm intervals. Contouring of target volume and organs at risk was carried out with a MULTIDATA workstation for regions of interest (mammaria interna and/or axillary and/or supraclavicular lymphatics and the breast or chest wall) as well as the organs at risk, such as heart and lung parenchyma. Planning target volume coverage was examined by three-dimensional isodose visualization for all CT axial sections for each patient. To determine the incidence of acute or late side effects on the lung parenchyma, conventional chest x-rays and CT studies were carried out at 1 month, 3 months and 6 months after completion of radiotherapy. Dose-volume histogram analysis revealed that this irradiation technique permits the application of a homogeneous dose to the target volume, conforming to the ICRU norms. The maximum dose applied to the ipsilateral lung parenchyma was less than 50-70% of the prescribed dose in the target volume. For left-located primaries, the highest dose applied to the myocardium is less than 30-50% of the dose in the target volume. Acute side effects, such as radiation pneumonitis, were noted in 8% (5/62) of the treated patients. Late side effects (grade I) in the lung were observed in 6.4% of the patients (4 patients) and occurred only in areas that had received more than 70% of the prescribed dose. We conclude that it is possible to apply a homogeneous dose distribution with a one isocenter multiple beams irradiation technique to the most complex target volume, such as the breast or chest wall and the locoregional lymphatics, with a minimum of side effects guaranteed.