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Session: Quality and Safety in Radiotherapy I [Return to Session]

Continuous Advanced Imaging and Real-Time Verification During Spine SBRT Delivery

A Kassaee*, R Scheuermann, A Butala, J Shabason, J Jones, D Mihailidis, University of Pennsylvania,Philadelphia, PA


SU-E-BRA-1 (Sunday, 7/10/2022) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]

Ballroom A

Purpose: Importance of continuous advanced imaging for intra and inter-fraction setup robustness during spine hypo-fractionated (SBRT) treatments.

Methods: Spine SBRT with two fractions to 24Gy requires high patient positional accuracy and reproducibility. We present a comprehensive and systematic study of 30 clinical cases (60 fractions) in which we trended the translational shifts (S) and rotational angles (R) performed prior and post-treatment with a series multiple advanced imaging on a Truebeam with a 6D couch. 2 or 4-arc VMAT was used for all cases. Image guidance session with kV-kV-imaging adjusted for S and R followed by CBCT focused on the CTV vertebrae and the two adjacent ones adjusted further for residual S and R with <6 min time restriction to start treatment delivery. Real-time Triggered Imaging (TI), every 20°-gantry angle, during treatment delivery was engaged for intra-fraction motion assessment and, a post-treatment CBCT performed for verification of setup robustness. Real-time TI lead to treatment interruption and mid-treatment CBCT to adjust offsets before resuming treatment, when necessary.

Results: We analyzed translational shifts and rotations between the initial kV-kV-imaging and subsequent pre-Tx CBCT and later with the post-Tx CBCT. We utilized thecal sac volume as surrogate during TI. After the kV-kV-pair, on average the values were 0.38cm, 0.37cm, and 0.36cm for vertical longitudinal and lateral shifts, respectively. For pre-Tx CBCT: 0.08cm, 0.06cm, 0.6cm. For post-Tx CBCT: 0.05cm, 0.04cm, 0.04cm. The rotations for the kV-kV-pair were 0.53°, 0°, 0.77° for pitch, roll, and yaw, respectively. For pre-Tx CBCT: 0.46°, 0.81°, 0.29°. For post-Tx CBCT: 0.22°, 0.17°, 0.15°. There is an overall all 1mm translational shift for up to 10 min treatment delivery.

Conclusion: Advanced imaging is crucial for spine SBRT. Combination of kV-kV and CBCT imaging allows higher accuracy of patient setup with increase in setup robustness by adding intra-fraction imaging and post-Tx imaging.


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