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In Vivo Quantitative Analysis of the Accuracy and Precision of Six Degree-Of-Freedom Prostate Motion Measurements During Patient VMAT Treatments

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J Kim

J-H Kim1*, D Nguyen1 , C Huang1 , R O'Brien1, T Fuangrod2 , V Caillet1,3 , P Poulsen4 , J Booth3 , P Keall1 , (1) The University of Sydney, Sydney, (2) Calvary Mater Hospital, Newcastle, NSW, (3) Royal North Shore Hospital, St Leonards, NSW, (4) Aarhus University Hospital, Aarhus


TU-H-605-8 (Tuesday, August 1, 2017) 4:30 PM - 6:00 PM Room: 605

Purpose: To characterise and quantitatively evaluate the accuracy and precision of six degree-of-freedom (6DoF) prostate target motion measured in real-time for patients undergoing VMAT treatments.

Methods: Among a cohort from a prospective clinical gating trial guided by kilovoltage intrafraction monitoring (KIM) during VMAT, first-ever real-time 6DoF intrafractional prostate motion was acquired in 14 patients (444 fractions). During each treatment kV and MV images were simultaneously collected at 10Hz along with KIM treatment log files containing the 6DoF prostate motion relative to its planning position calculated with an iterative closest point algorithm using the KIM-estimated 3D marker positions. The corresponding ground-truth target motion was obtained retrospectively based on kV/MV triangulation. The accuracy and precision of the 6DoF KIM motion estimates were calculated as the mean and standard deviation (s.d.) differences compared with the ground-truth.

Results: Translational prostate motion during the treatment was well-regulated to within <2.5 mm for 95% of the treatment time by gating motion>3mm, whereas the rotational motion was ≤9.1° for 95% of the treatment time. The accuracy and precision of real-time 6DoF KIM-measured prostate motion were 0.2° and 1.3° for rotations and 0.1 mm and 0.5 mm for translations, respectively. The precision of KIM-measured rotational motion was slightly gantry angle dependent and varied within ±2° for the entire gantry angle range, while the translational motion was all within ±1 mm. The magnitude of KIM-measured motion was well-correlated with the magnitude of groud-truth motion resulting in Pearson correlation coefficients of >0.9 in all DoF.

Conclusion: The results demonstrate that the KIM is capable of providing the real-time prostate target motion in 6DoF with an accuracy (±precision) of within 0.2±1.3° and 0.1±0.5 mm for rotation and translation, respectively. The findings of this study provide valuable insights towards real-time 6DoF tumour motion adaptive radiotherapy.

Funding Support, Disclosures, and Conflict of Interest: This project is supported by a Cancer Australia (1085360) grant.

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