A retrospective comparison of setup accuracy from CBCT and SGRT data in breast cancer patients

Both cone-beam computed tomography (CBCT) and surface-guided radiotherapy (SGRT) are used for breast patient positioning verification before treatment delivery. SGRT may reduce treatment time and imaging dose by potentially reduce the number of CBCT needed. The aim of this study was to compare the displacements resulting in positioning from the Image Guided Radiation Therapy (IGRT) 3D and SGRT methods and to design a clinical workflow for SGRT implementation in breast radiotherapy to establish an imaging strategy based on the data obtained.

For this study 128 breast cancer patients treated with 42.5 Gy in 16 fractions using 3D conformal radiotherapy with free breathing technique were enroled. A total of 366 CBCT images were evaluated for patient setup verification and compared with SGRT. Image registrations between planning CT images and CBCT images were performed in mutual agreement and in online mode by three health professionals. Student's paired t-test was used to compare the absolute difference in vector shift, measured in mm, for each orthogonal axis (x, y, z) between SGRT and CBCT methods. The multidisciplinary team evaluated a review of the original clinical workflow for SGRT implementation and data about patients treated with the updated workflow were reported.

Comparison of the shifts obtained with IGRT and SGRT for each orthogonal axis (for the x-axes the average displacement was 0.9 ± 0.7 mm, y = 1.1 ± 0.8 mm and z = 1.0 ± 0.7 mm) revealed no significant statistical differences (p > 0.05). Using the updated workflow the difference between SGRT and IGRT displacements was <3 mm in 91.4 % of patients with a reduction in total treatment time of approximately 20 %, due to the reduce frequency of the CBCT images acquisition and matching.

This study has shown that IGRT and SGRT agree in positioning patients with breast cancer within a millimetre tolerance. SGRT can be used for patient positioning, with the advantages of reducing radiation exposure and shorter overall treatment time.