ESTRO 37 Abstract book

S1172

ESTRO 37

2 Hong Kong Sanatorium & Hospital, Department of Radiotherapy, Hong Kong, Hong Kong SAR China

A single user, an experienced radiotherapy technician, performed the manual contouring (MC) and the editing of automated ABAS contours (UABAS) and DLC contours (UDLC). MC was used as the baseline method. User contouring/editing was performed with software employed in clinical practice (Eclipse, version 11.0, Varian, Palo Alto, U.S.A.), which includes semi-automatic contouring tools. For each contouring method MC, UABAS and UDLC, the time required to complete the task was recorded per patient and OAR. Only the times requires to manually edit the DLC and ABAS contours were recorded, not the times to generate them. Results Table 1 reports the median and inter-quartile ranges of user editing time for MC, ABAS and DLC contours. UABAS led to a median contouring time reduction of 7.8 minutes compared to MC, while UDLC led to a median time reduction of 10 minutes compared to MC. For the lungs, spinal cord and esophagus, UDLC times were significantly lower than UABAS (p<0.05). Times for both automatic methods were significantly lower than MC for all organs.

Purpose or Objective 3D volumetric MRI in abdomen for radiotherapy (RT) planning is challenged by the pronounced respiratory motion that compromises image quality and thus tissue delineation. Stereotactic body radiotherapy (SBRT) via abdominal compression (AC) could improve treatment delivery accuracy by restricting the respiratory motion. In this study, we aimed to evaluate whether AC could improve volumetric 3D MRI image quality and reduce diaphragm motion for SBRT. Material and Methods 8 healthy volunteers were recruited. Free breathing (FB) and 3 levels of AC (strong, medium and low) were applied using an adjustable screw. For each setting, a single slice sagittal cine image (TRUFI, TR/TE=355.7/1.6ms, voxel size=2.09x2.09x4mm 3 , scan time=16s) of medial right lung and T1w volumetric MR images (3D VIBE, TR/TE=6.68/2.39ms, voxel size=1.6x1.6x1.6mm3) covering thoracic and upper abdominal area were acquired 3 times on a 1.5T MR-simulator. The maximum positional shift of the dome of the diaphragm along SI and AP direction at each AC level was evaluated on the cine images using a custom matlab program based on cross-correlation . Organ edge sharpness, aliasing artifact and motion artifact were individually rated using a 5- point scale (point 1-5:worst-best). The image quality score at each AC level was compared using rank-sum test. Results The lowest image quality scores were associated with FB when compared with other levels of AC (organ edge sharpness:2.24±0.93 (FB), 2.30±0.85 (low), 2.50±0.81 (medium), 2.51±0.77 (strong); aliasing artifact:2.93±1.03 (FB), 2.94±0.90 (low), 3.18±0.88 (medium), 3.11±0.94 (strong); motion artifact:2.40±0.96 (FB), 2.56±0.85 (low), 2.52±0.80 (medium), 2.73±0.87 (strong)). Significantly lower score was only observed on motion artifact under FB (2.40±0.96 ) when compared with strong AC (2.73±0.87, p< 0.05). In terms of maximum positional shift, significantly smaller shift along anterior-posterior (AP) direction were observed under strong AC (1.25±0.99mm) when compared to FB (2.79±0.99mm, p<0.01) and other AC (low:2.56±1.43mm, p<0.01; medium: 2.04±0.06mm, p<0.01). When compared to medium (9.90±2.40mm, p<0.01) and strong (9.63±2.76mm, p<0.01) AC levels, significantly larger shift along superior-anterior(SI) direction were observed under FB (13.24±3.49mm, strong: p<0.01; medium: p<0.01) and low AC (13.21±4.70mm, strong: p<0.01; medium: p<0.05) Conclusion The abdominal image quality was generally improved under SBRT compression. In particular, motion artifact was substantially reduced under strong compression compared to FB. Respiratory motion induced positional shift was also significantly reduced under strong and medium AC compared to FB. EP-2126 4DMRI amplitude binning: better estimation of reconstructed motion at no cost in 4DMRI quality Z. Van Kesteren 1 , A. Van der Horst 1 , N. Onkenhout 2 , A. Bel 1 1 Academic Medical Center, Department of Radiotherapy, Amsterdam, The Netherlands 2 Vrije Universiteit, Faculty of Exact Sciences- Medical Natural Sciences, Amsterdam, The Netherlands Purpose or Objective 4DMRI is gaining popularity in radiotherapy of the upper abdomen, as it provides good soft tissue contrast and depicts the target motion during free breathing. The choice of applied binning strategy may influence imaging quality and potentially underestimate motion amplitude.

Figure 1 shows the fraction of time saved with respect to MC for the median values. For the lungs and the spinal cord, editing time for UDLC corresponded to a visual assessment of the contours with limited or no manual adjustments. Over all OARs, UABAS and UDLC led to a time saving of 41% and 64%, respectively, compared to MC.

Conclusion This investigation has demonstrated time savings for two OAR auto-contouring methods in the thorax. Editing the results of both methods provided significant time reductions for all OARs considered with respect to MC. DLC editing generated significant contouring time savings compared to ABAS for the lungs, spinal cord and esophagus. Future work will extend the time saving analysis to other body regions. EP-2125 Abdominal compression for SBRT: influence on 3D MRI image quality and diaphragm motion reduction O.L. Wong 1 , K.F. Cheng 2 , J. Yuan 1 , P.H. Fok 2 , Y.H. Zhou 1 , G. Chiu 2 , S.K. Yu 1 , K.Y. Cheung 1 1 Hong Kong Sanatorium & Hospital, Medical physics and Research, Hong Kong, Hong Kong SAR China