Abstract Book

S1189

ESTRO 37

orientations respectively (fig. 1). Even though most sources may be considered symmetrical, there were cases were a clear asymmetry was evident (TB6). The source shape reproduced a Gaussian profile with a RMSE of 2.9- 7.7% in the 100 – 10 % fluence region, while systematic deviations were evident in the lower tail region. Conclusion The reconstructed X-ray sources for six Varian TBs are in most cases symmetrical with FWHM values between 1.0 and 1.5 mm. The common approximation of a Gaussian profile, used by most beam models, might not be adequate for the tail region. Further investigation into the appropriate functional form is required. [1] Papaconstadopoulos et al PMB 61 (2016) 1078-1094

possible failure sources and potential alternatives for reducing the improbable occurrences. The lean instruments were considered for improving the process. The procedure was controlled over 6 months (Gen-Jun 2017). Results Applied shifts of 14948 consecutive fractions from 1353 patients were analyzed. No significant differences were observed over the 3 years (mean and SD were, respectively: 0.43±0.32cm, 0.43±0.32cm 0.45±0.33cm, showing an overall process stability. The major observed discrepancy was the monthly percentage of fractions with almost zero shifts (figure 1). Ishikawa fishbone method was adopted to recognize the artificial variability. Lack of confidence in applying shifts, reduced image quality, non-systematic use of automatic matching were considered as main con-causes of the discrepancy. Procedure harmonization to increase confidence in matching was implemented. In detail, (a) the DRRs parameters were personalized for the two projections (tangential and AP views); (b) the body and homo-lateral lung contours were exported with the DRR; (c) automatic pre-matching was performed, followed by manual fine tuning; (d) cases of corrections greater than 3mm were visualized aiming to help the RTT with the next shifts. In 2017, distribution symmetry improvement (Skewness moved from 1.4 to 1.1) and outlier reduction, verified by Kurtosis diminution, demonstrated a better “norma- lization” of the procedure after the LSSM (figure 2).

EP-2154 Lean-six-sigma methodology for improving quality in RT: the breast daily repositioning case P. Mancosu 1 , G. Nicolini 2 , G. Goretti 3 , F. De Rose 1 , D. Franceschini 1 , C. Ferrari 3 , S. Tomatis 1 , M. Scorsetti 4 1 Istituto Clinico Humanitas, Radiotherapy and Oncology, Rozzano Milan, Italy 2 Radiqa Developments, Medical Physics Team, Bellinzona, Swaziland 3 Istituto Clinico Humanitas, Lean Group, Rozzano Milan, Italy 4 Istituto Clinico Humanitas & Humanitas University, Radiotherapy and Oncology & Biomedical Sciences dept., Rozzano Milan, Italy Purpose or Objective According to the ESTRO booklet 4 guidelines, the concept of quality assurance in RT encompasses a comprehensive approach to all activities in the department. When hypofractionation regiment is adopted, the need of a continuous quality procedures updating is self-evident. At this aim, the Lean Six Sigma Methodology (LSSM) has been applied in our institute. LSSM was introduced in industry for providing near-perfect services to large processes, by reducing improbable occurrence. It consists of the synergetic adoption of two methods: (i) create a continuous process flow eliminating waste (Lean); (ii) reduce process variation (Six sigma) achieving the best quality. LSSM has been prospectively applied to breast patient repositioning. At our knowledge, this is the first time the LSSM has been rigorously applied to a RT process. Material and Methods Breast patients treated by hypofractionated RT in SIB delivered through VMAT technology with daily 2D-2D matching were considered. The five DMAIC (define, measure, analyze, improve and control) LSSM steps were applied by an interdisciplinary project team. The process was retrospective measured over 30 months (Jul2014– Dec2016) by querying the RT Record&Verify database. Cause&Effect relationships were analyzed, identifying

Figure 1 : Percentage of patients with shifts <0.1cm in function of month (before LSSM implementation).

Figure 2: Histogram of the shifts in function of year. Conclusion LSSM was successfully applied for the first time in a RT department, allowing the breast repositioning matching procedure to be redesigned. EP-2155 Dosimetry of the first synchrotron-based scanning proton beamline for the treatment of ocular tumors E. Mastella 1 , G. Magro 1 , A. Mirandola 1 , S. Molinelli 1 , S. Russo 1 , A. Vai 1 , D. Maestri 1 , A. Mairani 1,2 , M.R. Fiore 3 , C. Mosci 4 , F. Valvo 5 , R. Orecchia 6,7 , M. Ciocca 1