ESTRO 2022 - Abstract Book

S1255

Abstract book

ESTRO 2022

Results Figure 1 shows the couch shifts applied from SGRT system. From these values, the IGRT image registration deviations are displayed. Except for one patient, IGRT deviation values were within tolerances, so no additional couch shifts were performed after SGRT setup. The exception was for KV-MV with 0.6 cm deviation in vertical axis, meanwhile the CBCT deviation was 0.2 cm. For most patients the deviation obtained from CBCT registration was smaller (0.1±0.1, 0.0±0.1 and -0.1±0.2 in cm for vert, long and lat axes respectively) than the one obtained with orthogonal planar kV-MV imaging (0.0±0.2, -0.1±0.2, -0.1±0.2 cm vert, long, lat respectively). Even though the CBCT imaging was performed after kV-MV imaging and the patient could have moved. The percentages of patients with imaging derived differences within the interval [-0.2, 0.2] cm are shown in Figure 2.

Conclusion Optical 3D surface imaging for breast cancer patient setup positioning showed an excellent agreement with CBCT images (less than 2 mm residual for most patients) and better than for kV-MV. Positioning breast patients daily with SGRT could lead to a reduction to CTV to PTV margins without a cost of imaging dose linked to daily CBCT imaging.

PO-1480 Heart dose variability in RT of left breast cancer patients treated in deep inspiration breath hold

G. Johansson 1 , E. Fredén 1 , J. Knutsson 1 , M. Olin 1 , L. Dagertun 1 , A. Siegbahn 1,2

1 Södersjukhuset, Department of Oncology, Stockholm, Sweden; 2 Karolinska Institutet, Department of Clinical Sciences and Education, Stockholm, Sweden Purpose or Objective To evaluate the impact of the variability of the heart position and shape in the heart dose for patients with left-sided breast cancer who received external beam radiotherapy (RT) in deep inspiration breath hold (DIBH). Materials and Methods A total of 150 treatment fractions for 10 patients who received RT of left-sided breast cancer (2.67 Gy x 15 fx) with the DIBH technique were included in this study. The patients were initially positioned with the Catalyst (C-RAD, Uppsala, Sweden) surface scanning system in free breathing position. A CBCT scan was subsequently acquired in treatment position (DIBH) to derive the necessary couch translations to align the patient in accordance with the planning CT (pCT). The daily CBCT images were exported to the Monaco (Elekta AB, Stockholm, Sweden) treatment planning system (TPS). The online