Clinical Dosimetry Study Of Chest Wall Electron Beam Irradiation,3D-CRT And Combination Of X-Ray And Electron Beam 3D-CRT For Left Breast Cancer Patients After Modified Radical Mastectomy

Objective: To make a comparative study on the dosimetric characteristics of three treatment methods for the left breast cancer patients after modified radical mastectomy (MRM), including post-operative chest wall electron beam irradiation,three-dimensional conformal radiotherapy (3D-CRT) and the combination of X-ray and electron beam three-dimensional conformal radiotherapy.Methods: Altogether 15 patients with advanced left breast cancers who were treated with modified radical mastectomy in the Third Affiliated Hospital of Kunming Medical University from January 2014 to May 2015 were selected. The surface of left chest wall was filled up with 0.5cm-thickness equivalent filler. After the thermoplastic membrane was well fixed, CT positioning was performed. The Pinnacle3 9.10 three dimensional IMRT (Intensity Modulated Radiotherapy) treatment planning system was used to design three chest wall radiotherapy treatment plans for each patient, including electron beam irradiation plan (E Plan), 3D-CRT irradiation plan (3D-CRT Plan) and the combination of X-ray and electron beam irradiation 3D-CRT plan (3D-CRT+E Plan). The dosimetric parameters of target areas and OAR(Organs at Risk) of three plans : PTV: V90?V95?V100?V105?V110?0max?Dmin?Dmean?D5?D95?CI?HI and OARs: left-lung: V5?V10?V15?V20?V30?V40?Dmean; heart: V5?V10?V15?V20?V30?V40?Dmean; right-lung: Dmean were assessed and compared.Results:1. E Plan versus 3D-CRT Plan:(1) Comparison of target dose: V90?V95? V100?V110? Dmax? Dmin?Dmean?D95?CI and HI of the two groups were with statistically significant difference(P<0.05). There was no significant difference in V105 and D5 between the two groups(P>0.05).(2) Comparison of OARs dose: the statistically significant difference between the two groups was seen in V5?V10?V15?V20?V30?V40 and Dmean of left lung and V5?V10 and V15 of heart (P<0.05). There was no significant difference between the two groups in Dmeaa of right-lung and V20?V30?V40 and Dmean of heart (P>0.05).2. E Plan versus 3D-CRT+E Plan:(1) Comparison of target dose: V90?V95?V100?V110?Dmax?Dmin?Dmean?D5?D95?CI and HI of the two groups were with statistically significant difference(P<0.05). There was no significant difference in V105 between the two groups(P>0.05).(2) Comparison of OARs dose: the statistically significant difference between the two groups was seen in V5?V10?V15?V20?V30?V40 and Dmean of left lung and V5?V10 and V15 of heart (P<0.05). There was no significant difference between the two groups in Dmean of right lung and V20,?V30?V40 and Dmean of heart (P>0.05).3. 3D-CRT Plan versus 3D-CRT + E Plan:(1) Comparison of target dose: V105?Dmax? D5 and CI of the two groups were with statistically significant difference (P<0.05). There was no significant difference in V90?V95?V100?V110?Dmin?Dmean?D95 and HI between the two groups (P>0.05).(2) Comparison of OARs dose: the statistically significant difference between the two groups was seen in V5 and V10 of left lung and V5 of heart (P<0.05). There was no significant difference between the two groups in V15?V20?V30?V40 and Dmean of right lung and V10?V15?V20?V30?V40 and Dmean of heart (P>0.05).Conclusion: Chest wall radiotherapy alone is not recommended for routine use. Three dimensional conformal radiotherapy target area has been significantly improved in the conformity, uniformity and protection of Organs at Risk (OAR) in comparison with the simple electron therapy, which is also easier to implement clinically. 3D-CRT+E program does not show a clear advantage of the mixed rays. Therefore, post-operational chest wall radiotherapy for breast cancers is recommended to perform according to patients' actual conditions so as to develop individualized treatment plan.