ESTRO 2021 Abstract Book

S1140

ESTRO 2021

White dotted line: border between caudal and cranial half of NVB contours. Median interrater DSC NVB left = 0.62 (IQR: 0.59 – 0.65); right = 0.67 (IQR: 0.65 – 0.69). Median interrater DSC NVB caudal half left = 0.68 (IQR: 0.65 – 0.72); right = 0.68 (IQR: 0.63 – 0.70).

Figure 2: Representative case of contours of 4 raters of the IPAs

Median interrater DSC IPA left = 0.65 (IQR): 0.61 – 0.67); right = 0.64 (IQR: 0.60 – 0.66).

Conclusion The interrater agreement of the contours of the NVBs and IPAs on MRI was clinically acceptable considering their small spatial volume. The agreement was highest in the subset of the caudal half of the NVB, where agreement is most relevant for neurovascular sparing MRgRT for PCa. PO-1390 Intra-fraction prostate motion during stereotactic irradiation in 1st irradiation and re-irradiation A. TAILLEZ 1 , A.M. Bimbai 2 , T. Lacornerie 3 , M. Le Deley 2 , E.F. Lartigau 1 , D. Pasquier 1 1 Oscar Lambret Center, Academic Department of Radiation Oncology, Lille, France; 2 Oscar Lambret Center, Department of Biostatistics, Lille, France; 3 Oscar Lambret Center, Department of Medical Physics, Lille, France Purpose or Objective Knowing the intra-fraction prostate motion is crucial for prostate Stereotactic Body Radiation Therapy (SBRT). Cyberknife® (Accuray, Sunnyvale, CA, USA) enables the tracking of the target using fiducial markers. To date, no studies have focused on the intra-fraction prostate motion during re-irradiation by SBRT. The objective of this work was to evaluate these translational and rotational motions in primary treated patients and in a From January 2011 to March 2020, 162 patients with histologically proven prostate cancer received prostate SBRT, including 58 as part of a re-irradiation. Cyberknife® uses an orthogonal x-ray dual image monitoring system to monitor implanted gold markers. The coordinates of the fiducial markers were then collected. The translations and rotations were then calculated in relation to a reference point defined as the prostate position during the first follow-up image. The prostate deviation representing its overall movement was defined as the length of the 3D vector Results In total, 858 data files could be analyzed. Overall, we observed an increasing deviation over the first 30 minutes, with a stabilization afterwards (median=0.82, 1.94, 2.37, 2.74, 2.75 and 2.82 mm in the time intervals [0-10[, [10-20[, [20-30[, [30-40[, [40-50[, and [50-60]), related to movements in the three context of re-irradiation Materials and Methods