ESTRO 37 Abstract book

S1090

ESTRO 37

of the two opposing beams, resulting in ‘shells’ of high LET d surrounding the prostate as well as the index volume (Fig. 1b). As a result, both the rectum and the bladder had a region with elevated LET d values. The highest LET d in 1 cm 3 of the bladder ranged from 3.6 keV/µm for the patient with the smallest overlap between bladder and prostate to 5.3 keV/µm for the patient with the largest overlap. The highest LET d in 1 cm 3 of the rectum ranged from 3.5 to 4.1 keV/µm. The overall highest mean LET d values were found in the index lesion, with a tendency to increase with decreasing index volume (ranging from 2.7 to 3.7 keV/µm for the largest to the smallest volume). The RBE models (Fig 1c-e) increased the median mean dose of the prostate from 79.5 Gy(RBE 1.1 ) to 85.7 Gy(RBE MN ), with an even larger increase within the index, from 95.2 Gy(RBE 1.1 ) to 104.4 Gy(RBE MN ). The median mean dose for the bladder increased from 24.2 Gy(RBE 1.1 ) to 26.0 Gy(RBE MN ) and for the rectum from 6.5 Gy(RBE 1.1 ) to 7.0 Gy(RBE MN ). Conclusion The LET d distributions showed an increase towards the end of the proton beam trajectories. There were clear correlations between these distributions and the biological dose distributions from the RBE models. The RBE models predicted higher biological doses in the bladder, rectum, prostate and index compared to the generic RBE=1.1.

EP-2000 Image-based data mining with continuous outcome variables W. Beasley 1 , A. Green 1 , A. McWilliam 2 , E. Vasquez Osorio 1 , M. Aznar 1 , M. Van Herk 1 1 The University of Manchester, Faculty of Biology- Medicine and Health, Manchester, United Kingdom 2 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom