Session Item

Our center had newly installed a SGRT system on a bore-based LINAC. This study investigated the deep inspiration breath hold (DIBH) accuracy and reproducibility for left breast cancer patients using SGRT and bore-based LINAC.

30 patients were randomly selected retrospectively. The setup process of bore-based LINAC (Varian, Palo Alto, US) using SGRT system (Vision RT, UK) was divided into two parts: ceiling-camera setup and in-bore camera setup. Firstly, patient was positioned using the ceiling-camera to the free breathing surface. Patient’s rotational errors were adjusted manually by the therapist to less than 1˚ and translational errors were corrected via the LINAC couch. Patient was then instructed to take a deep breath and match with the DIBH surface at the vertical axis less than 0.5mm. The residual translational errors were corrected using the couch to near to zero. Next, the patient was loaded into the bore and the in-bore camera was activated. Before leaving the room, the patient was instructed to take another deep breath to make sure that all the SGRT parameters were less than 1mm and 1˚. The CBCT was acquired in DIBH, and 3D shifts were applied. A new reference surface for the session was captured after the couch shifts applied for monitoring. 3D shifts and 6D offline matching were recorded for data analysis.

A total of 438 CBCT images were analyzed. 2 patients’ treatment plans were changed to free breathing during the mid-course of the treatment. The mean absolute error and standard deviations for 3D were 0.17±0.16 cm, 0.37±0.3cm and 0.2±0.14cm in lateral, longitudinal and vertical directions. Whereas the mean absolute error and standard deviations for 6D were 0.16±0.13cm, 0.37±0.33cm, 0.22±0.14cm, 1.08±0.87˚, 0.64±0.54˚ and 0.95±0.74˚ in lateral, longitudinal, vertical, pitch, roll and yaw directions. Both 3D and 6D positioning accuracy were well within our setup protocol of 0.5cm and 2˚. The rotational errors of patients could be corrected adequately using SGRT system.

The use of SGRT system with bore-based LINAC is accurate and efficient for left breast cancer DIBH radiotherapy patients. In-bore SGRT system enables DIBH technique on bore-based LINAC. The robustness of bore-based LINAC shortens the breath hold duration for DIBH patients. This allows more patients to be eligible for DIBH treatment technique.