A new method to deliver supraclavicular radiation in breast radiotherapy for lung sparing

Due to the angulation of the breast board used for tangential breast irradiation, additional normal lung tissues are included in the supraclavicular field. This work investigates a method to reduce the lung volume and dose delivered during supraclavicular irradiation for breast cancer. Ten patients included for this retrospective study received chest wall and supraclavicular irradiation following radical surgery or breast-conserving surgery. Three-dimensional conformal radiation therapy plans were generated using the CMS XiO treatment planning system. The clinical target volume (CTV) of the supraclavicular irradiation is defined as the subcutaneous tissues from 0.5 cm under the anterior skin surface to a 3 cm depth. Only the ipsilateral lung is defined as the organ at risk. In the new method, the couch is rotated 90° and the supraclavicular field is tilted to maintain a normal incident angle to the breast board rather than the couch surface to spare more normal lung tissues. The absolute volume of the ipsilateral lung irradiated, and the volumes of lung tissues receiving 5 Gy and 20 Gy (V₅ and V₂₀) are analyzed. The new method can reduce the lung volume irradiated by the supraclavicular field significantly. For the ten patients investigated, only 5.3% of the ipsilateral lung is irradiated with the new method, while 14.9% of the ipsilateral lung is irradiated using the conventional method. Compared with the conventional method, the new method reduces V₅ by 53.6% and V₂₀ by 59.0%. Our new method does not alter the patient positioning for breast treatment but rotates the couch to deliver a tilted supraclavicular field to maintain adequate CTV coverage and spare more normal lung tissues. The results of this study demonstrated that our new method is effective, and that the reduction of normal lung tissue volume in the field is significant.