Dosimetric analysis of two contour guidelines for left breast cancer after breast conserving surgery
Objective To evaluate the dosimetric characteristics of two contour guidelines by RTOG and ESTRO for left breast cancer after breast conserving surgery.Methods From September 1,2020 to October 31,2021,16 consecutive left breast cancer after breast conserving surgery were enrolled.According to the ESTRO and RTOG guidelines,the regional lymph node areas and whole breast were delineated.For comparison,in the ESTRO guideline,axilla level 2 and interpec-toral nodes were delineated together,and named as axilla level Ⅱ,axilla level 3 named as axilla level Ⅲ,and lymph node level 4 named as supraclavicular.Each patient designed two volume modulated arc therapy plannings:PTV-E(ESTRO guideline)and PTV-R(RTOG guideline).The prescription dose was 50 Gy per 25 fractions,and the relevant dosimetric parameters of each plan were recorded.SPSS 23.0 software was used for statistical analysis.The two groups were com-pared by paired t-test.Results The volume of axilla level Ⅱ according to ESTRO and RTOG guidelines were(46.0± 11.1)cm3 and(16.6±4.7)cm3(t=12.461,P＜0.001).The volume of supraclavicular according to ESTRO and RTOG guidelines were(11.5±2.6)cm3 and(29.1±7.4)cm3(t=-9.465,P＜0.001).The mean dose,V5,V20,V30 to ipsi-lateral lung in the PTV-E plan were(8.9±0.9)Gy,(40.2±3.2)％,(13.9±2.5)％and(8.7±2.0)％,respectively,compared to(8.2±1.0)Gy,(37.6±4.1)％,(12.1±2.4)％and(7.6±2.0)％in the PTV-R plan(all P＜0.05).The mean doses of thyroid in the PTV-E and PTV-R plans were(11.4±7.4)Gy and(27.3±4.2)Gy,respectively(t=-7.392,P＜0.001).The maximum doses to the brachial plexus nerve in the PTV-E and PTV-R plans were(54.4± 0.7)Gy and(54.3±1.0)Gy,respectively(t=0.122,P=0.904),V30 were(32.1±11.1)％and(73.5±13.2)％,re-spectively(t=-7.964,P＜0.001),and V50 were(20.7±8.9)％and(31.0±17.8)％,respectively(t=-2.284,P=0.037).Conclusion The exposure doses of organ at risk for both contour guidelines meet clinical needs.The volume of supraclavicular nodes according to the ESTRO guideline is smaller,and the doses of thyroid and brachial plexus nerve are lower than RTOG guideline.
breast neoplasms/radiotherapyaxillary lymph nodes/radiotherapytarget delineationguidelinedosimetry
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