The comparision of the wide tangential - electron combination technique with photon - electron combination technique on the radiation of mammaria interna field during left breast radiotherapy and the analysis of cardiac doses

Purpose: In this study, it is aimed to research the effect of the wide tangential and electron combination technique (WTE) and photon-electron combination technique (P-E) on heart doses during the radiation of the mammaria interna field (MI) through virtual planning by making use of planning treatment Computerized Tomography (CT) of the patients diagnosed with left breast cancer who have received radiotherapy after breast conserving surgery (BCS).Patients and Method: The planning images archived of the first 30 patients, who have been applied BCS and radiotherapy in our clinique since March 2008 with left breast cancer diagnosis, are used. For each patient, external contour, mammaria interna, heart, lung and contralateral breast volume countoured in CT cross sections and two separate planning was carried out. In photon-electron technique, left breast was planned with two tangential co-planar fileds. It was calculated as 2 Gy fraction dose per day and 50 Gy in total. Mammaria interna field width was an approximately 4-5 cm and was planned with angles to the adjacent to tangential field as photon electron combination in SSD 100. Photon field doses were calculated 6 fractions with 6 MVX energy and total 12 Gy. The other dose left was completed total 38 Gy with 6-21 MeV electron in 19 fractions to the same field. In wide tangential ? electron (WTE) planning technique, left breast was planned in two tangential co-planar fields with medial and lateral tangential borders in P-E technique and calculated totally 38 Gy with 2 Gy fraction doses. At the same time, the MI dose left was completed with the electron energies and doses in the first planning. After 38 Gy, the medial border of the wide tangential field was moved to the lateral border of the MI field in P-E technique and lateral border to the the lateral border of the tangential field. 12 Gy RT in total with 2 Gy fractions is planned for this field. Following the choice of the appropriate isodose for treatment, dose volume histograms (DVH) of two separate plans were evaluated. For each patient, from the DVH in two planning, 50% (D50), 40% (D40), 30% (D30), 20% (D20), 10% (D10) dose received by percentage of heart volume, the maximum (Dmax), median (Dmedian) and average (Davr) doses received by heart volume, percentage of heart volume that received 10 Gy (V10Gy);the maximum (Dmax), median (Dmedian) and average (Davr) doses received by lung volume, percentage of lung volume that received 20 Gy (V20Gy);20% (D20) dose received by percentage of contralateral breast volume, the maximum (Dmax), median (Dmedian) and average (Davr) doses received by contralateral breast volume were tested. All statistical analysis was performed with SPSS for windows version 13.0 program. The ?paired samples test? was used for statistical analysis.Results: When two plannings were compared for the heart, D50, D40, D30, D20, D10, V10Gy, Dmax, Dmedian, Davr were found 8 Gy, 10.6 Gy, 13.5 Gy, 18.2 Gy, 27 Gy, 7.9 Gy and 11 Gy in P-E technique; 4.3 Gy, 5.7 Gy, 8.7 Gy, 13.9 Gy, 22.5 Gy, 47.2 Gy, 4.2 Gy and 8.3 Gy in GTE technique, respectively. A statistically significant difference was observed in favour of GTE technique for heart (p<0,0001). A statistically significant difference was found in favour of GTE technique for D20, Dmedian, Davr of lung. When we evaluated contralateral breast doses between P-E and GTE plans only for the maximum dose value a statistically significant difference was observed in favour of GTE technique (p=0.001).Conclusion: When the P-E and GTE technique were compared for heart, lung and contralateral breast doses after MI radiotherapy in the patients who underwent breast conserving surgery, GTE technique protects the heart more specifically without causing any dose increase in the contralateral breast and lung.Key Words: Left breast cancer, Mammaria Interna Radiatherapy, Wide Tangential, Heart doses