Deformation of prostate and seminal vesicles relative to intraprostatic fiducial markers.
OBJECTIVE
To quantify the residual geometric uncertainties after on-line corrections with intraprostatic fiducial markers, this study analyzed the deformation of the prostate and, in particular, the seminal vesicles relative to such markers.


METHODS
A planning computed tomography (CT) scan and three repeat CT scans were obtained for 21 prostate cancer patients who had had three to four cylindrical gold markers placed. The prostate and whole seminal vesicles (clinical target volume [CTV]) were delineated on each scan at a slice thickness of 1.5 mm. Rigid body transformations (translation and rotation) mapping the markers onto the planning scan positions were obtained. The translation only (T(only)) or both translation and rotation were applied to the delineated CTVs. Next, the residue CTV surface displacements were determined using nonrigid registration of the delineated contours. For translation and rotation of the CTV, the residues represented deformation; for T(only), the residues stemmed from deformation and rotation. T(only) represented the residues for most currently applied on-line protocols. The patient and population statistics of the CTV surface displacements were calculated. The intraobserver delineation variation was similarly quantified using repeat delineations for all patients and corrected for.


RESULTS
The largest CTV deformations were observed at the anterior and posterior side of the seminal vesicles (population average standard deviation </=3 mm). Prostate deformation was small (standard deviation </=1 mm). The increase in these deviations when neglecting rotation (T(only)) was small.


CONCLUSIONS
Although prostate deformation with respect to implanted fiducial markers was small, the corresponding deformation of the seminal vesicles was considerable. Adding marker-based rotational corrections to on-line translation corrections provided a limited reduction in the estimated planning margins.
van der Wielen
Gerard J
GJ
Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
Mutanga
Theodore F
TF
Incrocci
Luca
L
Kirkels
Wim J
WJ
Vasquez Osorio
Eliana M
EM
Hoogeman
Mischa S
MS
Heijmen
Ben J M
BJ
de Boer
Hans C J
HC
D000465:Algorithms; D015415:Biomarkers; D006801:Humans; D008297:Male; D015588:Observer Variation; D019047:Phantoms, Imaging; D011467:Prostate / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted; D020266:Radiotherapy, Conformal; D012669:Seminal Vesicles / Q000000981:diagnostic imaging* / Q000473:pathology*; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder
D015415:Biomarkers