ESTRO 37 Abstract book

S1118

ESTRO 37

EP-2040 Clinical Implementation Of Electromagnetic Transponders For Real-Time Tracking In Lung SBRT G. Dipasquale 1 , F. Caparrotti 1 , A. Dubouloz 1 , M. Jaccard 1 , B. Rakotomiaramanana 1 , C. Picardi 1 , J. Plojoux 2 , P. Gasche 2 , J. Miralbell 1 1 Radiation Oncology, Department of Radiation Oncology- Geneva University Hospital, Geneva 14, Switzerland 2 Pneumology, Department fo Pneumology- Geneva University Hospital, Geneva, Switzerland Purpose or Objective To describe the clinical implementation in our institution of electromagnetic transponders (EMT) in the treatment of early stage non small cell lung cancer with stereotactic body radiotherapy (SBRT), and to address intrafraction motion. Material and Methods Two patients (pts) underwent diagnostic bronchoscopy which confirmed the malignant nature of a suspicious lesion. During this procedure, pts were implanted with lung-specific EMT (Calypso™) in bronchi proximal to the tumor. A simulation 4DCT-scan was acquired for planning for both pts. For the second, a deep inspiration breath hold scan (DIBH) was also acquired. An internal target volume (ITV) was generated for the 4DCT-scan plans. We prescribed 60 Gy in 8 fractions (fx) to the planning target volume (PTV; PTV ITV =ITV+5mm or PTV DIBH = GTV+5mm) requiring 98% of the PTV to be covered by 95% of the dose. Modulated volumetric arc treatments (VMAT) plans with 2 full arcs (6MV FFF) were used for the first pt, while 2 half arcs were used to treat the second pt. PTV ITV volumes were 11.5 cc and 13.2 cc respectively for pt 1 and 2, while PTV DIBH was 9.1 cc (pt 2). For planning, setup and SBRT treatment, free breathing (FB) was used for pt 1, while DIBH was chosen for pt 2 (smaller PTV and better organ at risk sparing compared to a FB approach). Patient setup at LINAC used the mean EMT position calculated from the 4DCT-scan and the fixed position from the DIBH data respectively for pt 1 and pt 2. A cone beam CT (CBCT) followed, in FB or DIBH respectively for pt1 and pt 2, before each treatment to visualize tumor and EMT position to compare to planned position (Fig1.). EMT motion was recorded real-time, interrupting SBRT when a threshold of 3 mm in any directions was trespassed for the mean EMT position. Results SBRT was successfully delivered during an overall treatment time of 18 days, with excellent objective patient tolerance and no acute toxicity. Mean setup time (mm:ss) per fx was 10:38 (SD 02:29) for pt 1 and 12:33 (SD 3.24) for pt 2, mean treatment time was 02:14 (SD 00:13) for pt 1 and 01:12(SD 00:02) for pt 2, geometrical residual between measured and planned mean EMT positions remained stable during SBRT with a max difference of 0.01 cm for the first pt (only 2 beacons implanted) and of 0.17 cm for pt 2 (3 beacons implanted). With FB, in 5/8 fx our tracking system detected EMT motion beyond tolerance, with automatic interruption of the beam with a maximum movement of 1.1cm which interrupted the treatment for 3 seconds for pt 1. DIBH allowed a 30% reduction in PTV volume. EMT allowed automatic beam interruptions when pt was coughing and fast re-alignment. Conclusion Using Calypso™ allowed to optimize treatment according to patient’s breathing capabilities, target motion’s and, target location. EMT positions were stable during treatment and allowed real-time tracking during lung SBRT, optimizing accuracy of high dose delivery to a moving target.

Electronic Poster: Physics track: Inter-fraction motion management (excl. adaptive radiotherapy)

EP-2041 Registration accuracy of high-speed single breath-hold kV-CBCT lung cancer imaging A. Arns 1 , J. Fleckenstein 1 , F. Schneider 1 , J. Boda- Heggemann 1 , Y. Abo-Madyan 1 , V. Steil 1 , F. Wenz 1 , H. Wertz 1 1 Universitätsmedizin Mannheim- Medical Faculty Mannheim- Heidelberg University, Department of Radiation Oncology, Mannheim, Germany Purpose or Objective With single breath-hold imaging, hypo-fractionated deep- inspiration breath-hold SABR of lung tumors can be accelerated and precision can be improved because motion artifacts can be reduced to a minimum. To enable single breath-hold kV-CBCT imaging within 10-15s, linac gantry speed was accelerated to 18°/s for patient positioning. To evaluate clinical applicability, registration accuracy was determined and compared to conventional, clinical kV-CBCT with slow gantry speed of 3°/s. Material and Methods A lung tumor SABR case was simulated with four different tumor-mimicking inlays in a thorax phantom and scanned at 10 different pre-defined positions with conventional, clinical CBCT (3°/s) and faster CBCT (18°/s). To assure precise positions, right-left (RL), cranio-caudal (CC) and anterior-posterior (AP) shifts were applied with optical tracking. For both conventional and faster CBCT, the imaging preset setup was 200° rotation, 120kV and 0.4mAs/frame. Registration to planning CT was applied (1) manually by two clinical experts, (2) automatically with the clinical software provided by the vendor, and (3) automatically by an in-house developed independent framework programmed with MATLAB. The offsets between the registration results and the known isocenter shifts were determined and compared. Results With optical tracking, the systematic error of the 10 random pre-selected isocenter shifts of up to 19mm was reduced to 0.05mm. The stochastic mean displacement error for all tumor-mimicking inlays, shifts and