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Updated: Oct 1, 2026
Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
Measurements and clinical consequences of prostate motion during a radiotherapy fraction
Aart J Nederveen1, Uulke A van der Heide, Homan Dehnad
1Department of Radiation Oncology, University Medical Center Utrecht, Heidelberglaan 100, MS Q00.118, 3584 CX Utrecht, The Netherlands. a.j.nederveen@radth.ruu.nl
Purpose:
Here we study the magnitude of prostate motion during the delivery of a radiotherapy fraction. These motions have clinical consequences for on-line position verification and the choice of margins around the target volume.
Methods And Materials:
We studied the motion of the prostate for 10 patients during 251 radiotherapy treatment fractions by assessing the position of implanted gold markers. Gold markers of 1 mm diameter and 5 mm length were implanted in the prostate before the start of the radiotherapy. We obtained movies during each fraction using an a-Si flat-panel imager. The markers could be detected in separate frames using a marker extraction kernel.
Results:
Marker displacements as large as 9.5 mm were detected in one fraction. The motion of the prostate is greatest in the caudal-cranial and the anterior-posterior directions. Within a time window of 2 to 3 min, deviations from the initial marker position, averaged over all patients, are 0.3 +/- 0.5 mm and -0.4 +/- 0.7 mm in the anterior-posterior and caudal-cranial directions, respectively.
Conclusions:
It appeared that on average, the intrafraction prostate motions did not result in margins larger than 1 mm, provided that the position verification is performed at time intervals of 2 to 3 min. Only for some patients performing more frequent position verification or adding extra margins of 2 to 3 mm is required to account for intrafraction prostate motions.
