Comparison of two radiation techniques in breast boost delivery

Introduction: In the treatment of breast cancer, breast conserving surgery (BCS) and whole breast irradiation is a usual technique. The influence of lumpectomy boost following breast radiotherapy is apparent, but there are different delivery methods. This work intended to compare the dosimetric parameters of electron beams and photon beams for boosting irradiation in breast cancer patients who experienced breast-conserving surgery and whole- breast irradiation.   Materials and Methods: In this study we compared plans for electron beams and photon beams boost irradiation for 32 breast cancer patients who experienced breast-conserving surgery. Each patient was firstly treated by whole breast irradiation (45 Gy in 25 fractions) and then followed by lumpectomy boost (10 Gy in 5 fractions) with either electron beam therapy or with photon, 16 patients in each group. The organs at risk (OAR) involved the coronary arteries, lungs, and skin. For dosimetric comparison, conformity index (CI), homogeneity index (HI), uniformity index (UI) and dose-volume parameters for the planning target volume (PTV), and OAR were studied.   Results: From 2015 to 2017, thirty-two (32) patients enrolled the study. There were 11 patients (35%) with stage IIA, 14 patients (44%) with stage IIB and 7 patients (21%) with stage IIIA. Median age was 52 years (range 42-73). In the case of CI and HI significant differences were found in approval of the photon boost but in the evaluation of UI no major difference was noticed between two techniques. For PTV coverage of V95% and V107% the photon plans was superior to that of electron plans. About OAR sparing, the photon beam reduced the high-dose volume with cost of an increased low-dose volume. The high-dose volumes increased with electron plans.   Conclusion: Data show that photon boost irradiation provides better coverage to the tumor bed and improved dosimetric parameters compared to electron boost, considered the fact that PTV coverage and OAR sparing were superior with photons. It can be conclude that in centers where electron beam therapy is not presented, photon beam can be used efficiently for lumpectomy boost