Comparison between dynamic wedge and physical wedge in the influence of dose to the contralateral breast and lung in radiotherapy for primary breast cancer / 中华放射肿瘤学杂志

ABSTRACT

Objective To compare the dose to the contralateral breast, ipsilateral lung, and the whole lung in the tangential field radiotherapy for primary breast cancer using the dynamic wedge or physical wedge. Methods With thirteen breast cancer patients chosen, the dose distribution was computed for the plan used in practical treatment with the dynamic wedge and physical wedge. Plans were compared using dose volume histograms for the contralateral breast, ipsilateral lung and the whole lung. As for the contralateral breast, the dose distributions were not computed for the whole breast but computed for the two regions similar to a rectangular area in the axial slice and parts of the whole breast. The mean dose was used to evaluate CB1, CB2 and ipsilateral lung, and V_ 20 was used to evaluate the whole lung. The treatment planning system used was Varian CadPlan. An ionization chamber in a water phantom was used to measure some point doses to simulate the dose to the contralateral breast. Results When using the 30? dynamic wedge, the mean dose to CB1 and CB2 was 1.5%-3.9% and 1.1%- 2.6% , and the mean dose to the ipsilateral lung was 4.1%-14.7%. When using the 30? physical wedge, the mean dose to CB1 and CB2 were 1.5%-4.4% and 1.2%-3.0%, respectively, and the mean dose to the ipsilateral lung was 4.4%-15.2%. The values of V_ 20 were equal. When using the 15? dynamic wedge, the mean dose to CB1 and CB2 decreased compared to 15? physical wedge, but the value reduced was smaller than when using 30? wedge. Also, the measured results verified that the dose to the normal tissue is reduced using the dynamic wedge. Conclusions The mean dose to the contralateral breast was reduced by using the dynamic wedge instead of the physical wedge, and the mean dose to the ipsilateral lung or V_ 20 is reduced or equal to each other. So the probability of normal tissue complication such as a second breast malignancy or pneumonitis associated with radiotherapy are likely to be reduced.