Abstract Book

S1115

ESTRO 37

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.

Conclusion Intra-fraction R and S are less than 3 mm and 4 mm, respectively, in 75% of the treatments with both definitions. Thus a smaller DIBH window could be used. The R and S intra-fraction results obtained by our centre are according to literature. Inter-fractions R and S are greater than intra-fraction results. Cerviño’s definition is more sensitive to differences. CWE is not correlated to reproducibility, stability nor OAR doses. [1] Cerviño et al.Using surface imaging and visual coaching to improve the reproducibility and stability of deep-inspiration breath hold for left-breast-cancer radiotherapy.Phys Med Biol2009;54 [2] Stock et al.Development and application of a real- time monitoring and feedback system for deep inspiration breath hold based on external marker tracking.Med Phys2006;33(8) 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