RESUMEN
Objective To compare the dosimetry between inversely optimised intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy using the field-in-field technique (FIF) for whole-breast radiotherapy with a boost to the tumor bed after breast-conserving surgery.Methods IMRT and FIF treatment plans were respectively performed and optimised for 9 patients with early stage leftbreast cancer after breast-concerving surgery.The prescribed dose of breast was 50.4 Gy in 28 fractions,1.8 Gy per fraction and that of tumor bed was 61.6 Gy in 28 fractions,2.2 Gy per fraction.The conformity index,the dose and volume for OAR( organs at risks),time of planning and treatment for the two plans were compared.Results The conformity index(CI) for IMRT was improved compared with the FIF in breast [(1.82±0.16) vs.(2.21±0.15)] and tumor bed [(1.19±0.04) vs.(1.59±0.11),t=2.08,3.97,P ＜ 0.05 ].There was no difference for V20 of ipsilateral lung and V30 of heart between two plans.The Dmax and Dmean of the contralateral lung of FIF were (5.41 ±2.76) and (0.51 ±0.10) Gy,lower than those of IMRT [ (25.72 ± 2.61 ) and (7.46 ± 0.39) Gy,t =-22.44,- 21.14,P ＜ 0.05 ].The Dmax and Dmean of the contralateral breast of FIF were (8.50 ± 5.61 ) and (0.47 ± 0.11 ) Gy,lower than those of IMRT [(27.73±4.30) and (6.38±0.48) Gy,t=-5.66,-14.83,P＜0.05].ForFIF,theV5of the contralateral lung and breast were (0.09 ± 0.09) ％ and (0.45 ± 0.45 ) ％,respectively,lower than those of IMRT,which were (84.66 ±3.06) ％ and (60.79 ±4.94)％ (t =-28.19,- 12.80,P＜0.05).The time of optimised plan was (61.57 ± 0.89) min for FIF and(241.28 ± 1.06) min for IMRT (t=-32.35,P＜0.05),and that of treatment were (16.14±1.42) min for FIF and (29.85 ±0.59) min for IMRT (t =- 8.82,P ＜ 0.05).Conclusions For patients with early stage breast cancer after breast-concerving surgery,IMRT could improve the conformity index of target but increase the dose of eontralateral lung and breast.However,FIF has advantage on the time of optimising plan and treatment.