ESTRO 2021 Abstract Book

S785

ESTRO 2021

Results From February 2020 to January 2021 sixteen patients (29 lesions ) received BM SRS (14-21 Gy). The whole procedure, from the first CBCT scan to the end of irradiation and subsequent CBCT, required a median time of 9 minutes [6-13]. Mean translational error was 0.0 ± 0.3 mm [-0.7; 0.9] in lateral direction, and -0.1 ± 0.5 mm [-1.4; 1.0] in longitudinal direction. A 2.2 mm maximum shift was recorded on the vertical axis, nevertheless the mean translation error was 0.1 ± 0.6 mm. Roll, pitch and yaw registered a mean value of -0.1 ± 0.3° [-0.8; 0.2], 0.0 ± 0.2° [-0.8; 0.2], and -0.1 ± 0.3° [-0.8; 0.4], respectively. The results are summarized in figure 2.

Conclusion This study demonstrated that homemade mouth-bite thermoplastic masks combined with CBCT, 6-DOF couchtop, and fast FFF treatment delivery allow minimal intra-fraction uncertainties in BM SRS, confirming the accuracy of PTV margin definition. The results are comparable to the declared specifics of SRS dedicated