DOSIMETRIC EVALUATION IN RADIOTHERAPY PLANS FOR TREATMENT OF LEFT BREAST CANCER WITH THREE-DIMENSIONAL TECHNIQUE CONFORMED TO FREE BREATHING AND MODERATE DEEP INSPIRATION (DIBH) WITH ACTIVE BREATHING COORDINATING SYSTEM

Currently the standard treatment for early stages in breast cancer is to combine surgery and adjuvant external radiotherapy. The function of breast irradiation is to consolidate the treatment, avoiding relapses or metastases. However, its benefits may present longterm risks and complications. Recent studies have shown increased cardiac and pulmonary complications for the treatment of left breast with increased absorbed dose. Recently, new techniques have been introduced to radiotherapy in order to minimize cardiac and pulmonary doses through Deep Inspiration Breath Hold (DIBH) breath control. This study aims to present a dosimetric evaluation of three-dimensional (3D) left breast planning using a conventional free-breathing technique and moderate deep-breathing (DIBH) with the active breathing coordinating system. In a retrospective study, 11 patients with early stage left breast cancer with a prescribed dose of 50 Gy in 25 fractions were selected, whose conventional 3D free-breathing planning did not reach the acceptable constraints, and were submitted to planning with DIBH. All patients received training on the functioning of the active breathing coordinator system prior to performing the new deep-inspired computed tomography simulation, with the same positioning as the previous DIBH simulation. After acquisition of the exam, and delineation of the OARs and target volumes bypassed by the radiologist, physicists elaborated the plans with tangent fields and subfields (field in field). The average of the results found in the planning for the conventional technique with free breathing compared to DIBH, dose reduction in DIBH, with cardiac average dose from 7.5 Gy to 5Gy, V25 <5% from 10% to 5%, V10 <6 % / 35% from 19% to 10%; and for pulmonary volume mean dose from 14.5% to 12.9%, V20 <30% from 28% to 26%, V10 <40% from 39% to 34%, V5 <50% from 50% to 44%. Even better V90 tumor volume coverage> 90% from 93% to 95%. Considering the results, the DIBH technique is a tool capable of reducing absorbed doses in the heart and lung, due to the increase in parasagital distance from the cardiac area to the chest wall, minimizing lung density, allowing margins reduction and better target volume coverage.