A dosimetric study of supine and prone treatment setups for breast cancer patients after breast conserving surgery / 中华放射医学与防护杂志

ABSTRACT

Objective To compare the dosimetric differences of the targets and organs at risk (OARs) for early stage breast cancer patients receiving intensity modulated radiotherapy (IMRT) with supine or prone setups after breast conserving surgery.Methods After breast conserving surgery,15 left breast cancer patients with large and pendulous breasts were selected.Their planning CT images were acquired with supine and prone orientations respectively,based on which IMRT plans of 2 tangential fields were developed using the same optimization parameters.Treatment plans of the two setups were evaluated by comparing the target dose distribution,the doses and irradiated volumes of the heart,left lung,and right breast,and the monitor units (MUs).Results Superior conformal index (CI) was observed in the plans of prone setup than the supine cases (0.79 ± 0.05 vs.0.72 ± 0.04,W =138,P ＜ 0.01).The homogeneity index (HI) of prone positioning was also better than that of supine setup (1.09 ±0.01 vs.1.12 ± 0.02,t =-4.7,P ＜0.01).The planning target volume (PTV) receiving 95％ of prescribed dose (V95％),and the minimum doses (Dmin) of the prone cases were significantly higher than the supine patients (t =7.1,6.4,P＜0.01).Higher mean doses (D) were observed in prone cases (W=153,P＜0.01).The maximum doses (Dmax) of the supine plans were lower than the prone cases (t =-3.6,P ＜0.01).The right breast volumes receiving 5 Gy doses or higher (V5) were less in the supine cases than the prone plans (W=160,P ＜0.01).The heart volumes received no less than 30 Gy (V30),D of the heart,and the left lung volumes received higher than 20 Gy or 5 Gy (V20,V5) of the supine plans were significantly higher than the prone cases (W =133,120,120,P ＜0.01).No significant difference was observed on the MUs.Conclusions For cancer patients with large and pendulous breasts receiving IMRT after breast conserving surgery,prone setup leads to better homogeneity of target dose distribution,and reduces the doses and irradiated volumes of the heart and lungs.