Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_8_3195 - Deep Inspiration Breath Hold for Lung Stereotactic Body Radiation Therapy With Electromagnetic Transponders for Real-Time Tracking

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Deep Inspiration Breath Hold for Lung Stereotactic Body Radiation Therapy With Electromagnetic Transponders for Real-Time Tracking
G. Dipasquale1, M. Jaccard1, F. Caparrotti1, A. Dubouloz1, B. Rakotomiaramanana1, C. Picardi1, J. Plojoux2, P. Gasche2, and R. Miralbell1; 1Radiation Oncology, Geneva University Hospital, Geneva, Switzerland, 2Department of Pneumology, Hopitaux Universitaires de Geneve (HUG), Geneva, Switzerland

Purpose/Objective(s): We report on the clinical implementation in our center of stereotactic body radiotherapy (SBRT) of early stage non-small cell lung cancer using deep inspiration breath hold (DIBH) controlled by real-time tumour tracking of implanted electromagnetic transponders (EMT). We aimed to evaluate the feasibility of such treatment, the gain in patient positioning reproducibility, and the dosimetric benefit compared to free-breathing (FB) SBRT.

Materials/Methods: During the diagnostic bronchoscopy of a patient, three lung-specific EMT were implanted into bronchi adjacent to the tumour. A week after implantation, a DIBH CT was acquired for planning. A dose of 60 Gy in eight fractions was prescribed to the planning target volume (PTV) and delivered with 6 MV FFF photon beams in two half volumetric modulated arcs. For comparison, planning was also performed on a FB CT with a PTV generated from an internal target volume obtained from delineation on each phase of a 4D-CT. Patient treatment set-up was performed in DIBH using the EMT barycenter position and with cone beam CT (CBCT) verification. Real-time tracking was undertaken by recording EMT motion and automatic interruptions of the beam-on mode when a deviation from the planned position above 3 mm in any direction was exceeded. Additional imaging (CBCT after and kV during SBRT) was also performed. We analyzed patient alignment and fractions delivery using DIBH and real-time tracking with EMT.

Results: The eight SBRT fractions were delivered as planned with good patient tolerance and no acute toxicity. The median [range] setup time per fraction was 11 [9.3-18.1] min and the treatment time was 1.2 min. Visual inspection of CBCT before SBRT revealed perfect alignment of the PTV, the lungs, the main bronchi and the external contour of patient confirming the good reproducibility of the DIBH position via the EMT tracking. This was further validated by end-of-session CBCT and kV images during SBRT. The positions of EMT remained stable during DIBH treatments with median [range] absolute shifts of 0.14 [0.00-0.37] mm. Automatic beam interruptions, triggered by detection of EMT positions out of tolerance due to patient coughing or releasing DIBH, occurred with a median of 5.5 times per fraction (range, 0-14). The DIBH planning succeeded to obtain better dosimetric results compared to FB. Thus, the PTV was 31% smaller, the V5 Gy of the treated lung decreased by 42%, the V20 Gy by 51%, and the V30 Gy by 56%. In addition, the mean and max dose to the adjacent main bronchus decreased by 36% and by 20%, respectively.

Conclusion: Tracking with implanted EMT permitted reproducible and fast DIBH positioning, and SBRT allowing to better spare the healthy lung when compared to FB.

Author Disclosure: G. Dipasquale: None. M. Jaccard: None. A. Dubouloz: None. B. Rakotomiaramanana: None. P. Gasche: None. R. Miralbell: None.

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