ESTRO 2021 Abstract Book

S1654

ESTRO 2021

With the exception of patient 7, a trend in decreased BV variation and overall time to treat (from CBCT1 to beam-on) was seen from patients 1 to 8. Mean time to treat and mean BV decreased from patient 1 (27.0min (range 3.6 to 179.2) and 24% (standard deviation (SD) 67%)) to patient 8 (14.6 min (range 4 to 96) and 20% (SD 15%)). Conclusion This work confirms new patient bladder filling instructions require time to adapt to. Future work will quantify the dosimetric impact of bladder filling variability, and identify solutions including, patient/staff education and appropriate patient hydration. PO-1941 Use of Chabner XRT® Radiation Bra in a large-breasted patient: a case report F. Cucciarelli 1 , E. Arena 1 , C. Di Carlo 1 , F. Fenu 1 , V. Panni 1 , L. Vicenzi 1 , M. Parisotto 2 , F. Patani 1 , M. Valenti 2 , G. Mantello 1 1 Azienda Ospedaliera Universitaria Ospedali Riuniti, Radiotherapy, Ancona, Italy; 2 Azienda Ospedaliera Universitaria Ospedali Riuniti, Medical Physics, Ancona, Italy Purpose or Objective Despite modern techniques, in the Radiotherapy (RT) of breast cancer patients undergoing conserving surgery, large pendulous breast often presents problems during simulation, planning and treatment, including increase of skin toxicity and incidental lung and heart dose. We report our experience with the first patient (pt) with large pendulous left breast treated using a Bra during RT and its effect on acute skin toxicity and lung and heart dosimetry. Materials and Methods In August 2020, a 59-year-old pt underwent an upper-central quadrantectomy with sentinel lymph node biopsy . The pathological examination reported invasive lobular carcinoma G3 according to Elston-Ellis with no evidence of lymphovascular invasion and negative margins; immunochemical pattern: ER/PgR: 99%; Ki-67: 30%; Her-2/neu negative; TNM Stage pT2 pN0 M0. During simulation the pt put on Chabner XRT® Radiation Bra (Bra) custom-fit adapted to ensure that the breast tissue was contained entirely within the Bra cup. The shoulder straps have been adjusted and all points of Velcro® attachment have been indexed. Thermoplastic polyurethane windows allowed visibility of skin and bony landmarks essential for repeatable pt position. Two mm slices-Computed Tomography scan (CT) was acquired with and without Bra in supine position on a breast board immobilization device, with both arms raised above the head and extended from the mandibular angle to the diaphragm. Whole breast CTV and CTV boost were defined in both CTs with and without Bra. Prescription dose was 40,05 Gy in 15 fractions (fts) to whole breast (WB) with a sequential boost of 10,68 Gy in 4 fts. Selected dose constraints were: Dmean ≤ 5Gy, V8Gy ≤ 30%, D5% ≤ 16 Gy to the heart; V16Gy ≤ 20%, V8Gy ≤ 35%, V4Gy ≤ 50% to the ipsilateral lung. All toxicities were evaluated using Common Terminology Criteria of Adverse Events (CTCAE) version 4.0 toxicity scale. Results 3D-CRT technique planning and Bra device allowed dose homogeneity, less lateral breast displacement with less heart and lung involvement, compared to plan without Bra. The dosimetric parameters were: for the heart Dmean = 2Gy, V8Gy = 2,3%, D5% = 6 Gy; for ipsilateral lung V16Gy = 16,8%, V8Gy = 26%, V4Gy = 44% (Figure 1). Daily IGRT showed optimal reproducibility. The treatment was well tolerated with low side effects. According to CTCAE, the pt presented Grade 1 erythema multiforme and Grade 1 fatigue, completely disappeared after one month of follow-up.