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. 2018 Mar 28:5:102-107.
doi: 10.1016/j.phro.2018.03.008. eCollection 2018 Jan.

Analysis of intra-fraction prostate motion and derivation of duration-dependent margins for radiotherapy using real-time 4D ultrasound

Eric Pei Ping Pang  1   2 , Kellie Knight  2 , Qiao Fan  3 , Sheena Xue Fei Tan  1 , Khong Wei Ang  1 , Zubin Master  1 , Wing-Ho Mui  4 , Ronnie Wing-Kin Leung  4 , Marilyn Baird  2 , Jeffrey Kit Loong Tuan  1   5
Affiliations

Analysis of intra-fraction prostate motion and derivation of duration-dependent margins for radiotherapy using real-time 4D ultrasound

Eric Pei Ping Pang et al. Phys Imaging Radiat Oncol. .

Abstract

Background and purpose: During radiotherapy, prostate motion changes over time. Quantifying and accounting for this motion is essential. This study aimed to assess intra-fraction prostate motion and derive duration-dependent planning margins for two treatment techniques.

Material and methods: A four-dimension (4D) transperineal ultrasound Clarity® system was used to track prostate motion. We analysed 1913 fractions from 60 patients undergoing volumetric-modulated arc therapy (VMAT) to the prostate. The mean VMAT treatment duration was 3.4 min. Extended monitoring was conducted weekly to simulate motion during intensity-modulated radiation therapy (IMRT) treatment (an additional seven minutes). A motion-time trend analysis was conducted and the mean intra-fraction motion between VMAT and IMRT treatments compared. Duration-dependent margins were calculated and anisotropic margins for VMAT and IMRT treatments were derived.

Results: There were statistically significant differences in the mean intra-fraction motion between VMAT and the simulated IMRT duration in the inferior (0.1 mm versus 0.3 mm) and posterior (-0.2 versus -0.4 mm) directions respectively (p ≪ 0.01). An intra-fraction motion trend inferiorly and posteriorly was observed. The recommended minimum anisotropic margins are 1.7 mm/2.7 mm (superior/inferior); 0.8 mm (left/right), 1.7 mm/2.9 mm (anterior/posterior) for VMAT treatments and 2.9 mm/4.3 mm (superior/inferior), 1.5 mm (left/right), 2.8 mm/4.8 mm (anterior/posterior) for IMRT treatments. Smaller anisotropic margins were required for VMAT compared to IMRT (differences ranging from 1.2 to 1.6 mm superiorly/inferiorly, 0.7 mm laterally and 1.1-1.9 mm anteriorly/posteriorly).

Conclusions: VMAT treatment is preferred over IMRT as prostate motion increases with time. Larger margins should be employed in the inferior and posterior directions for both treatment durations. Duration-dependent margins should be applied in the presence of prolonged imaging and verification time.

Keywords: 4D Clarity ultrasound system; Intra-fraction movement; Margins; Prostate; Real-time tracking.

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Figures

Fig. 1
Fig. 1
Illustration of the mean intra-fraction motion for each individual with respect to the 30-s blocks in the a) Superior/Inferior, b) left/right and c) anterior/posterior directions.
See this image and copyright information in PMC

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