Stereographic Targeting in Prostate Radiotherapy: Speed and Precision by Daily Automatic Positioning Corrections Using Kilovoltage/Megavoltage Image Pairs

Residual Seminal Vesicle Displacement in Marker-Based Image-Guided Radiotherapy for Prostate Cancer and the Impact on Margin Design

“…Then, the segmented markers were jointly registered to the markers in the CBCT scan, based on chamfer matching (16), obtaining translations, and rotations in three dimensions. The accuracy of marker registration, expressed as an average uniform fiducial registration error (FRE), was 0.24 mm, which is in accordance with the FRE found by Mutanga et al (17) The FRE was calculated as the RMS value over all patients of the RMS values over all fractions of the random displacement errors determined in each direction. The FRE is needed to calculate the target registration error (TRE) (see below).…”

Deformation of Prostate and Seminal Vesicles Relative to Intraprostatic Fiducial Markers

“…The corresponding residue displacements, as reported in this study, were added in quadrature to the S and s values of COM displacements remaining after SGT correction (21). The latter contribution consisted of the small residue errors (S #0.5 mm, s #0.8 mm in each direction) directly after on-line correction (8), as well as those caused by intrafraction motion. Kotte et al (22) performed a markerbased study on prostate intrafraction motion in 427 patients.…”

“…The latter displacements depend not only on the CTV shape, but also on the behavior of the seminal vesicle deformation in the presence of prostate rotations. Knowledge of these displacements is clinically relevant because on-line corrections are often limited to translation corrections (8,10). To our knowledge, this is the first study to quantify these rotation deviations in detail.…”

“…A reduction of the CTV-PTV margin can lead to lower toxicity (6). The CTV-PTV margin can be reduced to less than the commonly used 1 cm with image-guided radiotherapy or adaptive radiotherapy (7)(8)(9).…”

“…In our clinic, a fully automated method for fast and accurate daily on-line prostate positioning during external beam radiotherapy was developed for the Synergy system (Elekta, Crawley UK) and clinically implemented (8). This method, Stereographic Targeting (SGT), is based on intraprostatic fiducial markers that are imaged in a crossfire of megavoltage and kilovoltage beams, followed by fully automated image analysis and remotely controlled couch shifts.…”