Dosimetry of "Field-in-field" Intensity Modulated Radiation Therapy(FIF-IMRT) after Breast Conservation Treatment(BCT) in Breast Cancer

Objective To evaluate the dosimetry advantages of "field-in-field" intensity modulated radiation therapy(FIFIMRT) after BCT in breast cancer.Methods Twenty-five cases of patients after breast conserving surgery were carried out FIFIMRT plans and conventional radiation therapy(CRT) using Pinnacle7.4f planning systems,and the differences of two plans have been compared.Results The coverage index(CI) and habituation index(HI) of FIF-IMRT were 1.08 ± 0.01 and 0.58 ± 0.08,better than 1.12 ± 0.04 and 0.50 ± 0.07 of CRT(P0.05).In the left breast cancer,the V40 of the heart,coronary arteries,and ipsilateral lung of the FIF-IMRT were similar with the CRT(2.7 ± 1.8)% vs.(3.2 ± 2.5)%,(27.2 ± 15.4)% vs.(30.0 ± 16.6)%,(9.4 ± 2.3)% vs.(10.0 ± 2.6)%,P 0.05;but the V5 of the heart,coronary arteries and ipsilateral lung in FIFIMRT were more than CRT,(10.5 ± 4.5)% vs.(9.1 ± 3.5)%,(71.9 ± 17.6)% vs.(68.6 ± 15.9)%,(24.8 ± 6.2)% vs.(23.1 ± 6.2)%,P0.05.In the right breast cancer,the V40 of liver and ipsilateral lung of FIF-IMRT were similar with the CRT(2.2 ± 0.9)% vs.(2.1 ± 0.8)%,(7.7 ± 2.3)% vs.(8.0 ± 3.0)%,P 0.05;but in FIF-IMRT plan,the V5 of liver and ipsilateral lung were more than CRT,(6.5 ± 1.1)% vs.(6.1 ± 1.0)%,(24.2 ± 3.9)% vs.(23.6 ± 4.0)%,P0.05.The units of the machine in FIF-IMRT was(221 ± 20)MU,less than(388 ± 59) MU in CRT(P0.05).Conclusion The whole breast FIF-IMRT improves PTV dose distribution and decrease deterioration of the machine,but can not decrease the high-dose volume of normal tissue and improve the low-dose volume of normal tissue compared with CRT.