2434 - Accuracy of Patient Setup in Breast Cancer Radiation Therapy Using Cone Beam Computed Tomography and Surface-Guided Radiotherapy - A Comparative Analysis

A. Vivekanandan, S. Chaudhary, A. Aashita, A. Amritt, A. Ghosh, A. Dagar, A. Maiti, S. Hazarika, J. Raj, A. Sharma, K. Kamboj, Y. I. K N, A. Kumar, J. Sharma, D. N. Sharma, and S. Mallick; National Cancer Institute, All India Institute of Medical Sciences, New Delhi, India

Purpose/Objective(s): Radiation plays an integral role in the treatment of breast cancer. With advancements in technologies, nowadays conformal radiotherapy techniques have become a standard of care. Positional accuracy during radiation for breast cancer patients is traditionally done with cone-beam computed tomography (CBCT). Surface-guided radiotherapy (SGRT) is evolving as a promising alternative, which uses an optical tracking system for analysing surface topography that is matched with referenced CT. SGRT may reduce treatment duration and imaging dosage by lowering the number of CBCTs performed. This study aims to examine the displacements resulting in positioning from the Image Guided Radiation Therapy (using CBCT) and SGRT. Materials/

Methods: For this study,120 breast cancer patients with 60 patients in each arm were treated with 40 Gy in 15 fractions or 26 Gy in 05 fractions using either IMRT or 3D conformal radiotherapy. CBCT images were compared with SGRT. In the SGRT arm, CBCT was done after SGRT positioning to analyse and compare the accuracy of the SGRT technique. Image registrations between planning CT images and CBCT images were performed. Student’s paired t-test was used to compare the absolute difference in set-up errors, measured in mm, for Vertical(Z), Longitudinal (Y), and Horizontal (X) axes along with the degree of rotation in Pitch(P), Yaw(Y) and Roll (R)between SGRT and CBCT methods.
Results: Among 120 patients, the median age was 52 years (27-75), with 55% of patients having right-side carcinoma breast among both groups. Breast conservation surgery was done in 33% in SGRT versus 45% in the CBCT arm, 26 Gy dose was given to 50% in the SGRT arm and 70% in CBCT. Treatment volume in the SGRT group was 15% to breast only, 8.3%to Chest wall only and 76.7% received nodal radiation. CBCT group, 18.3% to breast only, 3.3%to Chest wall only and 78.4% received nodal radiation. Comparison of the shifts obtained with CBCT and SGRT for each axis revealed Z, Y, X, P, R and Y are 0.02,0.04,-0.11,0.29,-0.12, 0.32 for CBCT and 0.1,0.02,0.03,0.71,0.06 and 0.39 for SGRT. The results indicate no statistically significant differences between the groups in terms of Z (p=0.151), Y (p=0.760),p=0.332), Pitch (p=0.074), Yaw (p=0.385) and Roll (p=0.52) with a difference was observed in the X dimension (p=0.021). This result indicates that SGRT is on par with the CBCT imaging technique for patient positioning. With each CBCT, patients were exposed to a radiation dose of 0.9 to 1.6cGy, with SGRT alone resulting in the elimination of this dose.
Conclusion: CBCT and SGRT show high concordance in positioning patients during radiation in breast cancer patients within a millimetre tolerance. SGRT can be used for patient positioning, with the advantages of reducing radiation exposure and shorter overall treatment time.