ESTRO 2021 Abstract Book

S98

ESTRO 2021

group, versus 1.8, 2.0 and 0.6 respectively in the N2O group. Four patients in the VR group experienced mild nausea/vomiting or dizziness during the procedure. The preparation duration was higher in the VR group, with a similar duration for the removal itself. Conclusion Replacing a medical gas by a virtual reality device was feasible and led to acceptable levels of pain and anxiety. Prospective randomized trials are needed to confirm efficacy and to determine which patients could benefit the most from this approach. PH-0162 Evaluation of New Patient Positioning Workflow on Setup Efficiency and Accuracy G. Zhang 1 , H. Zhong 1 , Y. Gao 2 , H. Wu 2 , J. Liu 2 , D. Zhang 2 , B. Li 2 1 Shenzhen People's Hospital, Radiation Oncology Department, Shenzhen, China; 2 Shenzhen People's Hospital, Radiation Oncogy Department, Shenzhen, China Purpose or Objective Recently, SGRT (Surface Guided Radiation Therapy) has been the standard approach for breast patient setup and monitoring. We evaluated the newly introduced SGRT-based patient setup workflow in terms of efficiency and accuracy in our clinic. Materials and Methods 30 post-op breast conservative patients were divided into 2 groups equally: SGRT-based group (Group A) and skin marking-based group (Group B). In Group A, patient was first aligned near to the isocenter according to the surface using manual couch movement. After that, the therapist will activate the ‘move couch’ function on SGRT system to move the patient on the couch in 6 degrees of freedom to the treatment isocenter position. Group B’s patient was set up by the therapist with hands and manual couch movement to the treatment isocenter. CBCT were taken. Data recorded including translational shifts: lateral, longitudinal, vertical (x, y and z) and rotational shifts: pitch, roll and yaw (Rx, Ry and Rz). Setup duration was defined from the time patient lied on the couch top until before the start of CBCT or before radiation beam on (the day when CBCT is not required). The independent sample t-test was applied to both groups to evaluate the differences. Results 75 CBCT images were analyzed for the setup accuracy in each group. The average setup error and standard deviations of Group A were 0.12±0.11cm, 0.12±0.09cm, 0.13±0.08cm (x, y and z) and 0.33±0.43°, 0.56±0.50°, 0.50±0.52° (Rx, Ry and Rz). Whereas, Group B were recorded as 0.15±0.11cm, 0.22±0.16cm, 0.25±0.16cm (x, y and z) and 0.66±0.72°, 0.99±0.69°, 0.78±0.56° (Rx, Ry and Rz). The data has shown significant (p<0.05) in all directions except lateral statistically. The translational absolute error ≤ 0.3cm and rotational absolute error ≤1˚ in Group A and B were 94%, 97%, 97% (x, y, z) and 88%, 78%, 82% (Rx, Ry and Rz) ; 91%, 63%, 60% (x, y, z) and 74%, 53%, 67%(Rx, Ry and Rz) respectively. 224 sessions in Group A and 221 sessions in Group B of patient positioning duration were recorded. The average setup time of Group A and Group B were 130±27s and 202±31s. Group A setup workflow can improve the efficiency by 35.6% in average as compared to Group B.

Conclusion In comparison to current skin marking-based setup workflow, SGRT-based workflow significantly increased the setup accuracy and workflow efficiency. The new patient positioning workflow has been implemented in our clinic successfully.