Dosimetric comparison of two intensity modulated radiotherapy modes for breast cancer after radical mastectomy / 中华放射医学与防护杂志

ABSTRACT

Objective To evaluate the dose distribution of target volume and normal tissues in forward intensity modulated radiotherapy (fIMRT) and inverse intensity modulated radiotherapy (iIMRT) modes for breast cancer after radical mastectomy.Methods Both fIMRT and iIMRT plans were developed for 10 patients with breast cancer after radical mastectomy.On each patient's CT images the supraclavicular area, chest wall, and internal mammary area were delineated.The prescription dose was 50 Gyin 25fractions.In the fIMRT plan X-ray irradiation at the dose of 6 MV was adopted for the supraclavicular and the chest wall areas and electron irradiation at the dose of 9 - 12 MeV was adopted for the internal mammary area, and the doses of cold and hot spots were adjusted according to the fitting doses of these 3 regions.In the iIMRT plan the supraclavicular area, chest wall, and internal mammary area were taken asa whole target, 6 MV X-rays was used, and inverse optimal design was performed.The dose distribution oftarget volume and normal tissues, conformal index (CI) , and heterogeneous index (HI) , and acceleratormonitor unit (MU) were analyzed using dose-volume histogram (DVH)for the two intensity modulated modes.Results The maximum dose of PTV of the iIMRT plan was significantly lower than that of the fIMRT plan(t = -3.23,P ＜0.05), the minimum dose and V95% of PTV of the iIMRT were significantly higher than those of the fIMRT plan(t = 4.08, -2.69, both P ＜0.05).The CI level of the iIMRT plan was significantly higher than that of the fIMRT plan and the HI level of the iIMRT plan was significantly lower than that of the fIMRT plan (t = -3.13, 2.74, both P ＜0.05).There were not significant differences in V10, V20, V25, V30, and Dmean of the ipsilateral lung between these 2 groups.However, the V15 of ipsilateral lung of the iIMRT group was significantly lower by 4.2% than that of the fIMRT group (t= 3.2, P ＜ 0.05).There were not significant differences in the mean dose (Dmean) and V30 of heart, and Dmean of contralateral lung and contralateral breast between these 2 groups.Conclusions Compared with fIMRT, the iIMRT plan results in more PTV coverage, higher conformity index, and more homogeneous dose distribution, with lower dose upon the lung at the affected side, and better protection of the contralateral lung, heart, and breast.