Abstract Book

S714

ESTRO 37

EP-1301 Incidental or intentional node irradiation in breast cancer. Preliminary results of OPTIMAL Trial. M. Algara 1 , J. López-Guerra 2 , A. Flaquer 3 , I. Beato 4 , F. Martínez 5 , J. Rodríguez 6 , X. Sanz 1 , J. Salinas 7 , M. Soler 8 , A. Frías 9 , G. Juan 10 , A. Manso 11 1 Parc de Salut Mar, Radiation Oncology, Barcelona, Spain 2 Hospital Virgen del Rocío, Radiation Oncology, Sevilla, Spain 3 Hospital Universitario de Araba, Radiation Oncology, Araba, Spain 4 Hospital Provincial de Castellón, Radiation Oncology, Castellón, Spain 5 Hospital Universitari La Fe, Radiation Oncology, Valencia, Spain 6 Hospital Universitario de León, Radiation Oncology, Leon, Spain 7 Hospital General Universitario Santa Lucía, Radiation Oncology, Cartagena, Spain 8 Hospital Universitario de la Ribera, Radiation Oncology, Alzira, Spain 9 Hospital Universitario de Cruces, Radiation Oncology, Barakaldo, Spain 10 Fundación Hospital de Jové, Radiation Oncology, Gijon, Spain 11 Hospital Universitario de la Paz, Radiation Oncology, Madrid, Spain Purpose or Objective To know the doses administrated to lymph node areas in a trial comparing intentional irradiation respect incidental irradiation in breast cancer, with low burden node involvement demonstrated by a molecular test. Material and Methods The OPTIMAL Trial is designed to show the non-inferiority of incidental irradiation, as compared to intentional irradiation of the auxiliary nodes in terms of 5-year disease-free survival of early breast cancer patients. Inclusion criteria were: patients with node negative early breast cancer, treated with conservative surgery and lymph node involvement tested by means OSNA ( One Step Nucleic Acid Amplification ) and total tumor load between 250-5000 copies (micro-metastasis) or between 5000- 15000 copies (macro-metastasis). Patients were randomized to intentional irradiation to breast and lymph node levels I to III and supraclavicular fossa (arm 1) or incidental irradiation were only treatment directed to breast was allowed (arm 2). In all cases, all lymph node areas and internal mammary chain were contoured, and measures of the dose administered to all contoured volumes were recorded. Patients were treated at standard fractionation of 2 Gy up to 50 Gy and a boost was administered according to guidelines of each participating department. Results More than 300 patients have been included and the first 247 have been analyzed (125 in arm 1 and 122 in arm 2). Patients presented micro-metastasis in 98 and 104 cases, and macro-metastasis in 23 and 14 patients of intentional or incident ghal arm respectively. Both arms were well balanced according to the characteristics of the patients: age, tumor, stage and molecular profile. The mean copies by OSNA in the range of micro-metastases were of 1263 in intentional arm and 1121 in incidental arm. The same values in the range of macro-metastases were 8682 and 7503 in the both arms respectively. There was on local relapse in intentional arm and 2 cases of metastatic spread in the incidental arm. There was no regional relapse in both arms. The mean doses at lymph node in arm 1 was 49.7 Gy at level I, 49.1 at level II, 49.4 Gy at level III, and 48.9 at supraclavicular fossa. The doses for the same node levels in arm 2 were 31.9 Gy, 18.8 Gy, 7.3 Gy and 1.4 Gy respectively. The median doses at internal mammary chain were similar i n both groups (23Gy in arm 1 and 16.7 in arm 2).

Conclusion At the moment there are no differences in local control, regional control and metastasis in both arms of the trial. The doses diminish as it increases the level of the lymph nodes in incidental arm. This trial should allow to know what extent of node areas must be irradiated in case of total tumor load in axillary nodes in the range of 250- 15000 copies by the innovative OSNA test. EP-1302 Impact On Cardiovascular And 2nd Tumor Risk From Nodal Rt In Breast Cancer: A Dosimetry Study A. Aranha Pereira Machado 1 , P. Mendes Maia 1 , C.V. Vicente Magiolino 1 , C. De Queioz Tannous 1 , A.C. Pellizon 1 , R.C. Fogarolli 1 , M. Jenwei Chen 1 , M.L. Gobo Silva 1 , D. Guedes de Castro 1 , T. Machado Coelho 1 , H. Ramos 1 , G. Rocha Melo Gondim 1 1 AC Camargo Cancer Center, Radiation Oncology, São Paulo, Brazil Purpose or Objective Irradiation of the internal mammary chain (IMC) and supraclavicular fossa (SF) has oncologic benefits in subgroups of breast cancer patients. Possible late side effects (LSEs), such as 2nd tumors and cardiovascular diseases, are a concern after the Radiotherapy (RT) of nodal chains. Perform the dosimetric analysis of Radiotherapy plans with the inclusion or not of SF and IMC and estimate whether the increase in mean doses (MD) in the heart and lungs with lymph node irradiation may lead to LSEs that may surpass the benefits of this treatment. Material and Methods In order to reduce the impact of individual anatomical variations, the dosimetric analysis was done in 30 treatment plans with 10 patients in 3 different situations: RT of the breast with boost in the tumor bed; with the inclusion of the SF or with the inclusion of SF and IMC. Contours were made according to the RTOG atlases by the same physician. Planning was made with Three- Dimensional Conformal Radiotherapy with 'Wide Tangents” and 'Field in Field” for homogeneity. Calculations of the increased risks of 2nd lung tumors and Cardiovascular disease with elective lymph node RT were made from the MDs variations found in the 30 planning sessions and their correlation with data published in extensive population databases¹ ¹ Carolyn Taylor, Candace Correa, et al. Estimating the Risks of Breast Cancer Radiotherapy: Evidence From Modern Radiation Doses to the Lungs and Heart and From Previous Randomized Trials. J.C.O. on March 20, 2017. Results RT with the inclusion of SF and IMC compared to breast exclusive RT increased the MD in the lung from 5.0 Gy to 8.1 Gy (Figure 1). RT planning with IMC coverage showed greater heterogeneity (greater V112) just as greater lung V5, V10 and V20 (Figure 2). The PTV IMC incidentally received 73.4% of the dose prescribed in RT plans without the intention of IMC coverage.

When the increase in MDs is correlated to the increase of LSE risks, it is found that the most important effect of elective lymph node RT is the increased risk of lung cancer, especially in patients who smoke (average increase in absolute risk = 1.38%). The increase in the