ESTRO 38 Abstract book

S1090 ESTRO 38

with a potential error of less than 2mm due to the mouse tool and the blurred edge of each anatomy image The distances measurements carried out on KV images indicate a diaphragm mean displacement of 3.8 mm (± 3.2 mm) in the cranio-caudal direction. The sternal position is pretty well reproducible with a mean variation of 1.4 mm (± 1.2 mm). The xiphoid moves slightly more 3.1 mm (±2.7 mm) in the anteroposterior direction. Conclusion The spirometric DIBH practice provides a reproducible lung volume which is important regarding the use of its DVH constraints. The distances measured on CT and KV images show an acceptable reproducibility and indicate the minimum PTV margins which have to be applied. Spirometric DIBH is safely used with high dose per session prescriptions often combined with VMAT and High Dose Rate FFF beams. EP-1995 Anisotropic definition of ITV-PTV margins according to the target position in lung SBRT with 4D- CBCT S. Pini 1 , G. Della Gala 2 , S. Russo 1 , M. Esposito 1 , L. Paoletti 3 , P. Alpi 3 , R. Barca 3 , S. Fondelli 3 , F. Rossi 3 , P. Bastiani 3 1 Azienda USL Toscana Centro, S.C. Fisica Sanitaria di Firenze-Empoli, Firenze, Italy ; 2 Scuola di Specializzazione in Fisica Medica, Università degli Studi di Firenze, Firenze, Italy ; 3 Azienda USL Toscana Centro, S.O.C. Radioterapia, Firenze, Italy Purpose or Objective 4D-CBCT has been increasingly used to evaluate lung tumor position and to validate the PTV margins during SBRT treatments.The aim of this study was to estimate the inter-fraction variability of respiratory-induced motion of target volumes in lung SBRT treatments. Material and Methods This study is a retrospective analysis on 59 patients receiving lung SBRT (276 fractions in total). 4D-CT scans for planning were obtained on a GE 4D-CT scanner. For breath control a compression abdominal belt was used. GTV was contoured on each of the multi-phases reconstructed images to generate ITV and PTV (ITV plus 5mm). Prior to each fraction, in-room 4D-CBCT image scan was acquired and registered to the planning CT by the Symmetry XVI Elekta system using an automatic two steps image registration: first an anatomical landmarks-based clipbox was defined for setup correction and then a mask of 5mm around PTV was created for the soft tissue registration. Matching results were used to shift the table along the LL-SI-AP directions (respectively left-right, superior-inferior, and anterior-posterior) to correct daily patient setup and tumor baseline shifts. The dual registration results were always reviewed by the physician and manually adjusted if not correct.The baseline shifts were measured by subtracting the clipbox suggested correction from the applied table shift. Tumour motion was quantified for each fraction as the absolute range of the respiratory cycle.The inter-fraction variability of the target motion was then evaluated for each patient, first, by calculating the difference between the max and min range of the respiratory cycle for all treatment fractions and then extracting the value corresponding to the highest discrepancy (fig.1).

EP-1994 Lung Radiotherapy : Internal position reproducibility with spirometric DIBH R. Garcia 1 , P. Mazars 1 , E. Jaegle 1 , V. Bodez 1 , C. Khamphan 1 , M.E. Alayrach 1 , A. Badey 1 , P. Martinez 1 1 Institut Sainte Catherine, Physics, Avignon, France Purpose or Objective Deep Inspiration Breath Hold (DIBH) is an interesting method that provides a simple process with a single CT free from internal movements influences. The use of a spirometer has been the first way to implement a breathing control. With a calibrate system, the inspired air volume is well controlled but does not guaranty the internal organs positions. Lung radiotherapy benefit a lot from DIBH but IGRT is needed to evaluate the internal reproducibility. Material and Methods The lung radiotherapy is driven with the help of the SDX TM spirometer and video feed back assisting the patient to provide a deep inspiration breath hold during each imaging and delivery phase. The anatomy position is evaluated with CT and KV images. The study is based on 30 patients who had a second CT during the course of treatment and 10 patients with KV images including the diaphragm. Multiple distances were defined and measured on the whole set of data. They concern the diaphragm, the apex, the sternum, the xiphoid, the heart, the carina and the abdomen. The lung volume, being and indicator of correlation with the dosimetry conditions, was measured and compared. Results

The mean lung volume of the 30 cases studied is 5256 cm3 (± 928 cm3). The mean lung volume difference between two CT acquisitions is 168 cm3 ± 390 cm3 (2 s), which represents a variation of 3.28% (±3.81%). The distances measurements carried out on CT images indicate a diaphragm mean displacement of 5.7 mm (± 4 mm), the abdomen width (A-P) of 7,3mm (5,9mm), the apex (H-F) 2,8mm(1,6mm), the carina (R-L) 2,4mm(1,8mm), the sternum (A-P) 2,5mm (2,&mm), the xiphoid (A-P) 3mm (3,4mm) and the heart (perpendicular to the ribs 4,1mm (3,4mm). The KV images measurements were obtained with the graphic rule on a stretched image area over the entire screen. The manual use of the graphic rule was evaluated