Objective:To study the differences of lung dosimetry in chest wall and supraclavicular area under two commonly used radiation positions during all X-ray irradiated radicalmastectomy radiation therapy(RMRT)

and to provide theoretical references for choosing the optimal radiation position with reduced radioactive damage. Methods:Totally 192 patients from January 2006 to December 2014 treated with RMRT on chest wall

supraclavicular and infraclavicular region

were included in the retrospective analysis.Among them

92 patients were in supine position and 100 patients were in sternal horizon position. The coverage of target and dose distribution of lung were evaluated according to the isodose curve and dose volume histograms of two groups. Results:The radiation treatment was successfully completed conducted for all patients. The volume and dose for the supine and sternal horizon positions were as follows:(1)the ipsilateral lungs:V20

(29.9±2.5)% and(32.4±3.2)%(P=0.000); V30

(24.8±6.3)% and(26.8±1.9)%(P=0.002);Dm

(16.4±3.0)Gy and(18.1±1.8)Gy(P=0.000).(2)the whole lung:V20

(14.6±2.1)% and(17.4±2.5)%(P=0.000);V30

(8.49±1.6)% and(13.9±1.7)%(P=0.000);Dm

(7.4±0.7)Gy and(8.2±0.7)Gy(P=0.000). The above results showed a significant difference in the lung dosimetry between the supine position and sternal horizon position. Conclusion:There is no significant difference between the two positions in dose distribution for RMRT. Supine position have significantly better dose distribution for lung than sternal horizon position.