ESTRO 37 Abstract book

S1109

ESTRO 37

Material and Methods The breast radiotherapy is driven with the help of a spirometer and video feed back assisting the patient to provide a deep inspiration breath hold during each imaging and delivery phase. The heart position was measured on the portal images compared to the DRR. The study contained 98 portal images of 15 patients having each three successive and weekly imaging controls. We defined three measurements with the heart image, the ribs and the inferior breast gland limit. One measurement was defined in the middle head-feet heart distance. The second was at the inferior breast gland limit and a third position was feet direction with the same gap of the two first positions.

3-infrafraction CB (IFCB) simultaneous to every arc delivery 4-6D correction of setup error before next arc, using HexaPOD robotic couch After every intrafraction image registration, time of imaging and 6D setup error are recorded and evaluated versus hypothetical setup error without any correction. Temporal evolution of setup error during treatment delivery are analyzed too. Results The magnitude of the mean setup error for the analyzed population was 0.91 ± 0.07 mm, less than 1 mm (p = 0.1). If no control or intrafraction correction had been performed, the average placement error would have been 1.43 ± 0.09. The values specified are the mean ± one standard deviation. In 3 cases of 80 image registration performed, a setup error greater than 2 mm have been found. If no intrafraction correction would have been applied, there would have been setup errors greater than 2 mm 13 times of 80 cone beam acquired. Figure 1 shows the temporal evolution of the mean total patient setup error. An increase of its magnitude with time is observed if no corrections were applied during the treatment session, as well as the application of those corrections keeps the maximum setup error around one millimeter as maximum.

Results The 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 with a potential error of less than 2mm due to the mouse tool and the blurred edge of each anatomy image.The mean / maximum heart position variation in the middle heart head-feet image was 0,36 / 0,51 cm. At the inferior breast gland limit we measured 0,32 / 0,52 cm and on the third position feet direction 0,30 / 0,58 cm. Some cine images were acquired with the objective to evaluate the intra-Breath-Hold movement but we could not highlight credible results inside 2 mm as read in some articles. Conclusion The heart position reproducibility during spirometric DIBH radiotherapy is fully acceptable. These results can be used to take into account the dosimetric effect in the dose gradient area on the heart edge. However, only the maximum dose can be evaluated as the mean dose would need a CB-CT and a deformable heart image process. R. Ricotti 1 , M. Seregni 2 , D. Ciardo 3 , S. Vigorito 4 , E. Rondi 4 , G. Piperno 3 , M.A. Zerella 5 , S. Arculeo 5 , C. Francia 5 , D. Sibio 5 , F. Cattani 6 , R. Orecchia 7 , M. Riboldi 2 , G. Baroni 8 , B. Jereczek-Fossa 5 1 Istituto Europeo di Oncologia, Radiotherapy Division, Milano, Italy 2 Politecnico di Milano, Dipartimento di Elettronica Informazione e Bioingegneria, Milano, Italy 3 Istituto Europeo di Oncologia, Division of Radiation Oncology, Milano, Italy 4 Istituto Europeo di Oncologia, Unit of Medical Physics, Milano, Italy EP-2027 Evaluation of target coverage in lung stereotactic radiotherapy with Cyberknife system

Conclusion Our analysis indicate that it is possible to perform spinal SBRT treatments with mean setup errors of less than 1mm, although a larger sample is needed to affirm with greater statistical significance. If no intrafraction corrections were applied according to the proposed protocol, an important part of the treatment would have been delivered with a setup error around 2 mm. This setup error can lead to an increase in absorbed dose of up to 13% in the spinal cord. EP-2026 Breast Radiotherapy : Heart position reproducibility with spirometric DIBH. R. Garcia 1 , P. Mazars 1 , E. Jaegle 1 , V. Bodez 1 , C. Khamphan 1 , M. Alayrach 1 , A. Badey 1 , P. Martinez 1 1 Institut Sainte Catherine, Physics department, Avignon, France Purpose or Objective Deep Inspiration Breath Hold (DIBH) is currently a standard practice to protect the heart during left breast radiotherapy. The increased lung volume pushes the heart in the opposite direction of the breast. This mechanical effect drives the heart away from the irradiate volume. Different systems are used to manage this breathing manoeuver which are based on surrogates. The spirometric method offers a guaranty of inspired air volume reproducibility. However, a question remains about the heart position reproducibility.