RESUMO
Objective To measure the displacement of the silver clips guided by kV-plain film at state of moderate deep inspiration hold(mDIBH) assisted by active breathing control(ABC) and to explore the margin of clinical target volume(CTV) to planning target volume(PTV) for breast cancer patients treated with three-dimensional conformal external-beam partial breast irradiation (EB-PBI) assisted by ABC. Methods The patients undertook CT simulation assisted by ABC to get the CT images on the respiratory condition of mDIBH. Four selected silver clips in breast cavity were delineated and the cavity based on all of the clips were delineated as gross tumor volume (GTV). Before each irradiation, two orthogonal kV-plain films were taken for the patients in the respiratory condition of mDIBH assisted by ABC device. 2D-2D auto-matie registration was performed based on pixel between the kV-plain films and the digital reconstructed radi-ographs(DRR). Then manual registration was undertook to get the shifts of the four clips separately at LAT, LNG,and VRT directions. Based on the shift data,the margins of CTV to PTV at LAT,LNG and VRT direc-tions were calculated. Results The margins from CTV to PTV were 5.00 mm,7.78 mm and 9.30 mm at LAT,LNG and VRT directions based on the clip at cephal border of the cavity. The corresponding margins were 4.40 mm,6.43 mm and 6.73 mm based on the clip at bottom of the cavity;5.04 mm,8.63 mm and 10.54 mm based on the clip at lateral border of the cavity;5.40 mm,8.59 ram and 10.81 mm based on the clip at pedal border of the cavity. Conclusions The silver clips in breast cavity can be clearly showed on the kV-plain film. The displacement of the clips can be exactly measured by registration of kV-plain film and planning DRR in condition of mDIBH assisted by ABC. The margins from CTV to PTV for EB-PBI can be calculated based on the displacement of the clips.