Dosimetric Comparison Of Intensity Modulated Radiation Therapy With Difference Clinical Target Volumes In Early Breast Cancer After Breast Conservative Surgery

Purpose:To compare the dosimetry differences between women treated with expansion of partial breast irradiation(EPBI) versus Whole breast irradiation (WBI) after breast conservative surgery of early stage breast cancer.Methods and Materials:1.30consecutive patients who underwent BCS for Early breast cancer from October2011to September2012have been in the study. We designed two different plans for each patient, one is the conventional whole breast irradiation, and another is the expansion of partial breast irradiation.2. Every target has been delineated of visual by CT. clinical target volumes (CTV) of conventional whole breast irradiation is consists of mammary glands. Furthermore, the CTV was kept at least5mm from the skin and did not include the chest wall. The CTV received50GY in25fractions and tumor bed boost of60GY in25fractions. CTV of the expansion of partial breast irradiation is the tumor bed expanded with3cm, but limited to the whole breast CTV.3. Irradiation dose is same to whole breast irradiation. Plans were normalized to50Gy to95%of the retracted PTV and60Gy to100%of the retracted GTV. Each plan must reach to the clinical standard.Results:1. With the target dose meeting the clinical requirement, the median clinical target volume (CTV1) of WBI treated was517cm3and the median planning target volume(PTV1) was726cm3. The median CTV2of EPBI treated was204cm3and PTV2was335cm’(P=0.000). 2. V20within ipsilateral lung is26%in the WBI plan, which is much higher than that of the EPBI plan (22%)(p=0.002). V30within ipsilateral lung is18%in the WBI plan, which is much higher than that of the EPBI plan (11%)(p=0.000). Skin of the maximum and mean value in the WBI plan are63.65GY and11.44GY, respectively, which are much higher than those in the EPBI plan (62.62GY and7.03GY)(P=0.007and P=0.011).3. Total monitor units set to511per fraction for25fractions in the WBI plan and426in the EPBI plan (P=0.002). The radiation dose of contralateral lung, whole lung, heart, spinal cord, contralateral breast are reduced in the EPBI plan.Conclusions:Compared to the partial breast irradiation, the expansion of partial breast irradiation increases the clinical target volume. A dosimetrical analysis showed that radiation dose of all jeopardized organs for expansion of partial breast irradiation are decreased compared with the whole breast irradiation. It is suggested that expansion of partial breast irradiation may be a new kind of radiotherapy in early breast cancer after breast conservative surgery. However, it needs to be confirmed by further clinical research.