Session Item

Intra-fraction prostate motion during stereotactic irradiation in 1st irradiation and re-irradiation
Alexandre TAILLEZ, France
PO-1390

Abstract

Intra-fraction prostate motion during stereotactic irradiation in 1st irradiation and re-irradiation
Authors:

Alexandre TAILLEZ1, André Michel Bimbai2, Thomas Lacornerie3, Marie-Cecile Le Deley2, Eric F Lartigau1, David Pasquier1

1Oscar Lambret Center, Academic Department of Radiation Oncology, Lille, France; 2Oscar Lambret Center, Department of Biostatistics, Lille, France; 3Oscar Lambret Center, Department of Medical Physics, Lille, France

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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 context of re-irradiation

Material and Methods

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 translational axes. The deviation over time in the group of primary treated patients was significantly larger than that of the group of patients who were re-irradiated, leading to a mean deviation of 2.73 (sd=1.00) versus 1.90 (sd=0.79), p<0.001.
Conclusion
This is the first study to focus on intra-fraction prostate motion in the context of re-irradiation. We observed that intra-fraction prostate motions persisted in the setting of re-irradiation although they were significantly reduced compared to first irradiation. These results will help to better estimate random error during the SBRT treatment of an intra-prostatic recurrence after irradiation.