| Objective The ACOSOG Z0011 and NSABP B-32 trials have provoked speculations regarding whether the incidental radiation dose to axillary lymph nodes(ALNs)with tangential radiation therapy fields could have prevented axillary recurrences in the sentinel lymph nodes(SLNs)-only arm;however,the unexpected control of internal mammary lymph node drainage(IMLN)that accompanies incidental IMLN irradiation has been an ongoing controversy,especially for 1-3-LN-positive breast cancer and high-risk,node-negative stage II breast cancer.In this current study,we evaluated the incidental coverage dose to the IMLN in patient treated with postmastectomy radiotherapy(PMRT),and analyzed the anatomic and technical parameters to the coverage of IMLN irradiation dose for patients who underwent modified radical mastectomy(MRM).Methods One hundred and thirty eight patients undergoing RT in our hospital for breast cancer were retrospectively analyzed.Patients were divided into three groups:three-dimensional conformal radiotherapy(3D-CRT)group,forward intensity-modulated radiotherapy(F-IMRT)group and inverse intensity-modulated radiotherapy(I-IMRT)group.The IMLN and clinical target volume(CTV)were contoured according to Radiation Therapy Oncology Group(RTOG)consensus,and were not include into the planning target volume(PTV).The incidental irradiation dose to IMLN among the three groups and the first three intercostal spaces(ICS1-3)were all compared,and explore the relationship between the mean doses(Dmean)of IMLN and the OARs(ipsilateral lung and heart).We analyzed the incidental IMLN irradiation dose coverage and its relationship with anatomic and technical parameters.Results Incidental IMLN irradiation dose ranged from 2.76 to 50.93 Gy(mean,32.85 Gy),and 10 of 138 patients(7.25%)treated with PMRT received ≥ 45 Gy.The dose delivered to IMLN showed no difference in CRT,F-IMRT and I-IMRT(33.80 Gy,29.65 Gy and 32.95 Gy).And 10.42%,2.04%,and 9.76%patients achieved>45Gy when treated with CRT,F-IMRT and I-IMRT.For the IMLN dose in the first three intercostal spaces(ICS1-3),there were no difference to the three treatment plannings.The Dmean,V20,V30,V40 and V50 of the ICS2 and ICS3 were all obviously superior than ICS1 for all these three plannings.Moderate positive correlation was founded between Dmean for IMLN and Dmean for heart for left breast cancer patients underwent CRT(r=0.338,P=0.01).Whereas for F-IMRT and I-IMRT groups,positive correlation were founded between Dmean for IMLN and Dmean and V20 for ipsilateral lung for all patients(F-IMRT:r=0.366,P=0.010;r=0.318,P=0.026;I-IMRT:r=0.427,P=0.005;r=0.411,P=0.008).Body weight,body mass index(BMI),body surface area(BSA),and thoracic transverse diameter(DT)were found to be lower in patients with incidental IMNI dose>45 Gy than in patients with incidental IMN dose<45 Gy.While planning target volume of IMN(PTVIMN)included in PTV(IMNin)and the ratio of IMNin to PTVIMN(RIMNin)were larger in patients with adequate incidental IMNI dose compared to patients with insufficient incidental IMN dose.In univariate analysis,the body weight,BMI,BSA,DT,ratio of D-T to the thoracic anteroposterior diameter(DAP),RIMNin and PTV posterior border were the parameters affecting Incidental IMLN irradiation dose.In multivariate analysis,body weight,DAP,DT,PTV volume,and RIMNin were correlative factors that affected Incidental IMLN irradiation dose.There were no significant relationships observed between the Dmean of the incidental IMNI dose and the magnitude of patient height,DAP,number of internal thoracic vessels,CTV/PTV/PTVIMN volume,CTV/PTV border,gantry angles,T-stage,N-stage or the radiation delivery technique for all patients.Conclusions There was a substantial dose was delivered to the IMLN for partial patients.Compared to 3D-CRT,although F-IMRT and I-IMRT decreasrd the OARs doses,IMLN accepted incidentally irradiated with a equal dose to 3D-CRT.With the equal dose distribution patterns for all three techniques,the mean dose of the heart was further decreased in the IMRT cohort(F-IMRT and I-IMRT),and no correlation was evident between the incidental dose to the IMN and the dose to the heart.The incidental IMNI dose was influenced by patients’ certain physical characteristics,anatomic characteristics and irradiation technical parameters(patient height,body weight,BMI,thoracic skeletal shape and RIMNin),when analyzing the correlation research,these clinical features should be taken into account. |
