Feasibility study on setting the breast board support plate angle to 0° / 中华放射医学与防护杂志

ABSTRACT

Objective To explore the feasibility to set the breast board support plate angle to 0° for breast cancer patient in the intensity modulated radiation therapy. Methods A total of 60 patients with breast cancer who received the simultaneous integrated boost intensity-modulated radiation therapy ( SIB-IMRT) after breast-conserving surgery were enrolled form Oct 2015 to Feb 2017. They were randomly divided into three groups that the angle of the breast board support plate was 12°, 7° and 0° respectively. The ipsilateral lung V20 , V5 , Dmean , the heart V10 , V30 , Dmean and the collimator angle were compared among three groups. In addition, the distribution of the setup error was analyzed and the group system error and random error were calculated. Results There were no statistically significant differences in the ipsilateral lung V20, V5, Dmean and the heart V10, V30, Dmean among the three groups(P >0. 05). The sum of the collimator angle and the angle of the support plate was about 13. 4° for each group. Only the setup error of z (vertical) direction was statistically different (χ2 =78. 32, P<0. 001) and the median of the 0° group was closest to the value 0 and the quartile spacing was the smallest. The absolute error of y ( longitudinal) , z directions was statistically different (χ2 =7. 63, 22. 61,P<0. 05). In the z direction, the absolute error was reduced as the angle of the support plate decreased and 0°group was the smallest. In the y direction, the absolute error at 12° was the smallest, but had little difference with that at 0°. Among three groups, the smallest system error of the x(lateral) direction and y direction was at 0°, while that of the z direction was at 12°. Conclusions To set the breast board support plate 0° is feasible. The angle of the support plate can be replaced by the collimator angle, while the setup error of z direction could be significantly reduced.