Evaluating the Use of SGRT on Left Breast DIBH: Target Accuracy and Cardiac Reproducibility

Abstract

<h3>Purpose/Objective(s)</h3> The use of SGRT in left breast DIBH has been broadly discussed in many studies, however the data on accuracy of both target and cardiac reproducibility are limited. We conducted a study to clinically evaluate its positioning accuracy and cardiac reproducibility. <h3>Materials/Methods</h3> 30 Patients with left breast (intact) treated with deep inspiration breath hold (DIBH) were selected. All treatments were done using a radiosurgery system and a motion tracking system. Each patient is set up using SGRT ‘move couch' function to automatically move the patient to the free breathing baseline position and then DIBH isocenter position. CBCT was acquired. Two steps image registration were executed. Firstly, image registration (Registration A) was done base on PTV and soft tissue auto-match and followed by second image registration. Second registration (Registration B) was matched manually base on cardiac tissue position (only translational directions). Cardiac reproducibility was defined as Registration B – Registration A where only translational shifts were involved. Both registrations were verified by the same radiation therapist to reduce inter-personal discrepancies. Statistical software was used for data analysis. <h3>Results</h3> A total of 275 CBCT images were analyzed. The mean of the absolute target positioning errors and standard deviations were 0.11 ± 0.08cm, 0.14 ± 0.11cm, 0.13 ± 0.10cm (lateral, longitudinal and vertical) and 0.79 ± 0.66˚, 0.69 ± 0.57˚, 0.73 ± 0.64˚ (pitch, roll and yaw). The average of cardiac position discrepancies was 0.01 ± 0.30cm, 0.05 ± 0.34cm, 0.01 ± 0.09cm in lateral, longitudinal and vertical directions. <h3>Conclusion</h3> DIBH technique displaced the heart postero-inferiorly and distant from treatment target. SGRT-based DIBH for left breast irradiation resulted in good reproducibility in both target and cardiac. Cardiac sparing effect is promising.