Abstract Book

S720

ESTRO 37

Purpose or Objective Radiotherapy plays a key role in the local control of breast carcinoma. The prone positioning of patients allows a significant reduction of the doses in the organs at risk. The aim of this study is to compare two prone protocols of positioning in patients with breast carcinoma in order to minimize systematic and random errors due to positioning. Material and Methods In the analysis of prone positioning, a total of 20 patients were studied (8 positioned with protocol 1 and 12 with protocol 2). In protocol 1, three tattoos have been performed, one in the midline in the dorsal region and two lateral leveling tattoos at mid-level of the torso in the anterior–posterior dimension. In protocol 2, four tattoos have been placed, two lateral leveling tattoos at mid-level of the torso in the anterior–posterior dimension, a third posterior tattoo, on the back of the patient, off-midline in the direction of the breast side that is being treated, and a fourth placed in the breast, in the middle towards the costal wall.The treatments were performed hypofractionally, distributed in 15 fractions of 2.67 Gy/fraction in breast, and 0.3 Gy /fraction in the PTV Boost concomitantly.The evaluation of the results obtained for both protocols was performed, using Excel and SPSS, analyzing the Levene’s test to test for homogeneity of variances with a significance level p = 0.05. Results Positioning of prone patients in protocol 2 leads to a decrease in systematic errors of 0.26 cm (p = 0.03) in the lateral component, 0.19 cm (p = 0.04) in the vertical component and 0.17 cm (p = 0.04) in the longitudinal component in relation to protocol 1 (table 1). Random errors are also reduced and consequently reduce the margins by 0.69 cm in the lateral component, 0.52 cm in the vertical component and 0.49 cm in the longitudinal component in relation to protocol 1 (table 2).

and mortality of patients treated after 15 years. That is why it is necessary to look for new formulas in order to reduce the doses in the organs at risk even more, maintaining the local control and survival rates. In this study, we evaluate prone positioning versus supine in 3D techniques of radiotherapy in patients with breast carcinoma, analyzing the absorbed dose in surrounding risk organs, lung and heart. Material and Methods A total of 34 patients (16 positioned in prone and 18 in supine) have been studied. All treatments considered are located in the left breast. Every treatment has been performed hypofractionally, distributed in 15 fractions of 2.67 Gy/fraction in breast, and 0.3 Gy/fraction in the PTV Boost concomitantly. Mean doses in PTV breast and in PTV Boost have been analyzed. Mean doses in lung and heart as well as V20, V5 lung and V30 and V20 heart have also been evaluated. The evaluation of the results obtained for both positions was made, using Excel and SPSS, with the independent sample t-test, which compares mean value of both samples with a significance level p = 0.05 (table 1).

Results The mean PTV boost doses and the percentage of volume irradiated between 95% and 107% of the prescribed dose are very close to both patient positions.The mean PTV breast dose and the percentage of volume irradiated within the 95% of prescribed dose presented similar values for both positions. A significant decrease in mean dose (p <0.01), V20 (p <0.01) and V5 (p <0.01) in the lungs was observed in the prone patients, as well as in the mean dose (p = 0.01), V20 (p = 0.02) and V30 (p = 0.02) in heart versus those placed in supine position (figure 1).

Conclusion The placement of tattoos in protocol 2 of prone positioning allows reducing systematic and random errors in a significant way, so a better reproducibility of treatments is achieved. It‘s essential to improve the quality of radiotherapy treatments in order to reduce the doses of organ at risk. EP-1313 Dose optimization in conventional breast radiotherapy through positioning: supine vs prone D. Hernández González 1 , M. Roch González 1 , P. Castro Tejero 1 , P. García Castañón 1 , M.T. Murillo González 2 , C. Ansón Marcos 1 , A. Viñals Muñoz 1 , L. Pérez González 1 1 H.U. LA PRINCESA, Medical Physics, Madrid, Spain 2 H.U. LA PRINCESA, Radiation Oncology, Madrid, Spain Purpose or Objective Complete irradiation of breast improves local control and survival of breast cancer, although increased morbidity

Conclusion The prone positioning for radiotherapy treatments of breast carcinoma reflects a decrease in the dose, in relation to supine positioning, in nearby risk organs, especially in the lung, obtaining coverage and mean doses of PTV breast and PTV Boost very similar for both positions.