SU‐E‐J‐152: Fluoroscopic Treatment Verification for Gated Stereotactic Body Radiation Therapy of a Tumor Located Near the Dome of the Liver: A

Purpose: To describe a method using pretreatment and intrafraction fluoroscopic verification of the gated treatment of a liver lesion located near the diaphragm. Methods: A 74‐year‐old female patient, who had previously received radiation to the lung, presented with a 13.8 cc tumor located 0.5 cm inferior to the superior border of the liver, moving 2 cm in the cranio‐caudal direction with breathing. A planning CT with contrast in full exhale breath hold (FEBH) was acquired to reduce motion artifact, followed by a 4‐dimensional (4D) CT. The gross target volume (GTV) was contoured on the FEBH CT and propagated only to the 25% inspiration (25In) and 25% expiration (25Ex) phases of the 4D‐CT, in order to reduce lung dose. An internal target volume (ITV) was created encompassing all 3 phases. A plan was created to deliver 50 Gy to the PTV (ITV+0.3cm laterally and inferiorly) in 5 fractions using 3D conformal planning gated on the FE, 25In and 25Ex phases. Digitally reconstructed radiographs (DRR) were created for each beam angle and for each of the 3 respiratory phases included in the gating window. Prior to treatment, a mega‐voltage (MV)‐CBCT was acquired and its projections were analyzed in cine‐mode. Intrafraction motion verification was monitored using MV‐fluoroscopy. On both cine and fluoroscopy movies, the respiratory phase was identified using the position of the diaphragm, and the frames were compared to the corresponding DRRs. Results: Qualitative analysis on both the pretreatment cine and intrafraction fluoroscopy movies showed a clinically acceptable agreement between plan and treatment position. Conclusion: We described a treatment verification method for gated SBRT of lesions near the dome of the liver, using pre‐treatment and intrafraction fluoroscopic movies. This method is a good gated treatment quality assurance tool allowing to confidently spare lung tissue.