Open Access Highly Accessed Research article

Real-time prostate motion assessment: image-guidance and the temporal dependence of intra-fraction motion

Avilash K Cramer1, Amanu G Haile2, Sanja Ognjenovic2, Tulsee S Doshi3, William Matthew Reilly4, Katherine E Rubinstein5, Nima Nabavizadeh6, Thuan Nguyen7, Lu Z Meng8, Martin Fuss6, James A Tanyi69* and Arthur Y Hung6

Author Affiliations

1 Brown University, Providence, RI, USA

2 Oregon State University, Corvallis, OR, USA

3 Stanford University, Stanford, CA, USA

4 Pomona College, Claremont, CA, USA

5 Whitman College, Walla Walla, WA, USA

6 Department of Radiation Medicine, Oregon Health & Science University, Portland, OR, USA

7 Department of Public Health & Preventive Medicine, Oregon Health & Science University, Portland, OR, USA

8 Department of Radiation Oncology, University of California Davis Comprehensive Cancer Centre, Sacramento, California, USA

9 Department of Nuclear Engineering & Radiation Health Physics, Oregon State University, Corvallis, OR, USA

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BMC Medical Physics 2013, 13:4  doi:10.1186/1756-6649-13-4

Published: 23 September 2013



The rapid adoption of image-guidance in prostate intensity-modulated radiotherapy (IMRT) results in longer treatment times, which may result in larger intrafraction motion, thereby negating the advantage of image-guidance. This study aims to qualify and quantify the contribution of image-guidance to the temporal dependence of intrafraction motion during prostate IMRT.


One-hundred and forty-three patients who underwent conventional IMRT (n=67) or intensity-modulated arc therapy (IMAT/RapidArc, n=76) for localized prostate cancer were evaluated. Intrafraction motion assessment was based on continuous RL (lateral), SI (longitudinal), and AP (vertical) positional detection of electromagnetic transponders at 10 Hz. Daily motion amplitudes were reported as session mean, median, and root-mean-square (RMS) displacements. Temporal effect was evaluated by categorizing treatment sessions into 4 different classes: IMRTc (transponder only localization), IMRTcc (transponder + CBCT localization), IMATc (transponder only localization), or IMATcc (transponder + CBCT localization).


Mean/median session times were 4.15/3.99 min (IMATc), 12.74/12.19 min (IMATcc), 5.99/5.77 min (IMRTc), and 12.98/12.39 min (IMRTcc), with significant pair-wise difference (p<0.0001) between all category combinations except for IMRTcc vs. IMATcc (p>0.05). Median intrafraction motion difference between CBCT and non-CBCT categories strongly correlated with time for RMS (t-value=17.29; p<0.0001), SI (t-value=−4.25; p<0.0001), and AP (t-value=2.76; p<0.0066), with a weak correlation for RL (t-value=1.67; p=0.0971). Treatment time reduction with non-CBCT treatment categories showed reductions in the observed intrafraction motion: systematic error (Σ)<0.6 mm and random error (σ)<1.2 mm compared with ≤0.8 mm and <1.6 mm, respectively, for CBCT-involved treatment categories.


For treatment durations >4-6 minutes, and without any intrafraction motion mitigation protocol in place, patient repositioning is recommended, with at least the acquisition of the lateral component of an orthogonal image pair in the absence of volumetric imaging.

Prostate cancer; Real-time motion tracking; Intrafraction variation; Treatment margin; Treatment time