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Prostate bed motion may cause geographic miss in post‐prostatectomy image‐guided intensity‐modulated radiotherapy
Author(s) -
Bell Linda J,
Cox Jennifer,
Eade Thomas,
Rinks Marianne,
Kneebone Andrew
Publication year - 2013
Publication title -
journal of medical imaging and radiation oncology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.31
H-Index - 43
eISSN - 1754-9485
pISSN - 1754-9477
DOI - 10.1111/1754-9485.12089
Subject(s) - medicine , prostatectomy , prostate , sagittal plane , prostate cancer , radiation therapy , nuclear medicine , anatomy , surgery , cancer
There is little data to guide radiation oncologists on appropriate margin selection in the post‐prostatectomy setting. The aim of this study was to quantify interfraction variation in motion of the prostate bed to determine these margins. Methods The superior and inferior surgical clips in the prostate bed were tracked on pretreatment cone beam CT images ( n = 377) for 40 patients who had received post‐prostatectomy radiotherapy. Prostate bed motion was calculated for the upper and lower segments by measuring the position of surgical clips located close to midline relative to bony anatomy in the axial (translational) and sagittal (tilt) planes. The frequency of potential geographic misses was calculated for either 1 cm or 0.5 cm posterior planning target volume margins. Results The mean magnitude of movement of the prostate bed in the anterior–posterior, superior–inferior and left–right planes, respectively, were as follows: upper portion, 0.50 cm, 0.28 cm, 0.10 cm; lower portion, 0.18 cm, 0.18 cm, 0.08 cm. The random and systematic errors, respectively, of the prostate bed motion in the anterior–posterior, superior–inferior and left–right planes, respectively, were as follows: upper portion, 0.47 cm and 0.50 cm, 0.28 cm and 0.27 cm, 0.11 cm and 0.11 cm; lower portion, 0.17 cm and 0.18 cm, 0.17 cm and 0.19 cm, 0.08 cm and 0.10 cm. Most geographic misses occurred in the upper prostate bed in the anterior–posterior plane. The median prostate bed tilt was 1.8° (range −23.4° to 42.3°). Conclusions Variability was seen in all planes for the movement of both surgical clips. The greatest movement occurred in the anterior–posterior plane in the upper prostate bed, which could cause geographic miss of treatment delivery. The variability in the movement of the superior and inferior clips indicates a prostate bed tilt that would be difficult to correct with standard online matching techniques. This creates a strong argument for using anisotropic planning target volume margins in post‐prostatectomy radiotherapy.