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Fluoroscopic Treatment Verification for Gated Stereotactic Body Radiation Therapy of a Tumor Located Near the Dome of the Liver: A Case Study

O Gayou

O Gayou*, J Christensen, A Kirichenko, Allegheny General Hospital, Pittsburgh, PA

SU-E-J-152 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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.

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