ESTRO 36 Abstract Book

S884 ESTRO 36 _______________________________________________________________________________________________

The junction in case of pat3 was covered by the 90% isodose (except near the skin). The D99-value shows that this treatment plan was cold compared to the other plans. Conclusion Measures are needed to prevent the occurrence of extreme hot and cold spots in the junction due to DIBH variation: This modified technique provides a damping effect on the occurrence of dose extremes. To create an extra buffer against underdosage, D99 of the CTV at the junction should be high enough, eg 95%. The technique presented is well tolerated by the patient. EP-1631 Reproducibility of DIBH tecnique guided by an optical system: the florence usl experience S. Russo 1 , F. Rossi 2 , G. Stoppa 2 , L. Paoletti 2 , S. Fondelli 2 , R. Barca 2 , P. Alpi 2 , B. Grilli Leonulli 2 , S. Pini 1 , M. Esposito 1 , A. Ghirelli 1 , L. Cunti 2 , L. Isgrò 2 , M. Verdiani 2 , P. Bastiani 2 1 Azienda USL Toscana Centro, Medical Physics Unit, Florence, Italy 2 Azienda USL Toscana Centro, Radiotherapy Physics Unit, Florence, Italy Purpose or Objective Aim of this work was to evaluate interfraction and intrafraction reproducibility of a deep inspiration breath- hold (DIBH) tecnique based on optical surface tracking technologies for selected patients undergoing adjuvant RT for left-sided breast cancer. Material and Methods 30 patients that underwent left side adjuvant radiotherapy were included in this study. Prospective gating CT imaging was performed by Sentinel™ (C-RAD Positioning AB, Sweden) laser scanner system and a Siemens BrightSpeed CT scanner. Base line level and gating window amplitude of the respiratory signal was established during CT simulation procedure. Gated treatments delivery was supported by the Catalyst™ system (C-RAD Positioning AB, Sweden) connected with an Elekta Synergy linear accelerator (Elekta AB, Sweden) via the Elekta Response™ Interface. The treatment beam was turned on only when the patient signal is within the previously established gating window. Visual coaching through video goggles were provided to help the patient following the optimal breathing pattern. Treatments were performed in DIBH with 3D conformal tangential beams for 50 Gy median dose to the whole breast in 25 fractions. The reproducibility of the DIBH during treatment was monitored by comparing the reference CT surface with the 3D surfaces captured by Catalyst TM system during BH before and after treatment delivery. Interfraction and intra-fraction variability were quantified in mean and SD displacements in traslation (Lat, Long, Vert) and rotations (Rot, Roll, Pitch) in the isocenter position between the reference and the live surface over all the treatment fractions of the enrolled patients. Results Inter-fraction variability before treatment delivery was extremely reduced: the group mean translational and rotational errors were respectively lower than 0.4 mm and 0.7° in all directions. After treatment delivery the group mean shift was lower than 2 mm in all direction and no difference in rotations was observed. Intra-fraction variability was <2.1 mm in translations and <1° in rotations. The cumulative distribution of interfraction mean shift during BH before (BT) and after (AT) treatment delivery for the patients undergoing BH treatment is shown in figure. Separate contributions from Lateral, Longitudinal,and Vertical direction were reported.

Conclusion In our experience DIBH procedure guided by optical systems for left breast irradiation is a reproducible and stable tecnique with a a limited inter-fraction and intra- fraction DIBH variability. EP-1632 A motion monitoring and processing system based on computer vision: prototype and proof of principle N. Leduc 1 , V. Atallah 2 , A. Petit 1 , S. Belhomme 1 , V. Vinh- Hung 3 , P. Sargos 1 1 Institut Bergonié, Radiation Oncology, Bordeaux, France 2 University Hospital of Bordeaux, Radiation Oncology, Bordeaux, France 3 University Hospital of Martinique, Radiation Oncology, Fort-de-France, France Purpose or Objective Monitoring and controlling respiratory motion is a challenge for the accuracy and safety of therapeutic irradiation of thoracic tumors. Systems based on the monitoring of internal or external surrogates have been developed but remain costly and high-maintenance. We describe here the development and validation of Madibreast, an in-house-made respiratory monitoring and processing device based on optical tracking of external markers. Material and Methods We designed an optical apparatus to ensure real-time submillimetric image resolution at 4 m. Using code libraries based on OpenCv, we optically tracked high- contrast markers set on patients' breasts. Validation of spatial and time accuracy was performed on a mechanical phantom and on human breast. A simple graphical interface allowed the user to vizualise in real-time the in- room motion of the markers during the session. Results Madibreast was able to track motion of markers up to a 5 cm/s speed, at a frame rate of 30 fps, with submillimetric accuracy on mechanical phantom and human breasts. Latency remained below 100 ms. Concomitant monitoring of three different locations on the breast showed discrepancies in axial motion up to 4 mm for deep- breathing patterns. Figure 1 displays an example of user