Endorectal MRI assessment of local relapse after surgery for prostate cancer: A model to define treatment field guidelines for adjuvant radiotherapy in patients at high risk for local failure.
OBJECTIVE
To assess the role of endorectal magnetic resonance imaging (MRI) in defining local relapse after radical prostatectomy for prostate cancer to help to reassess the clinical target volume (CTV) for adjuvant postprostatectomy radiotherapy.


METHODS
Sixty patients undergoing an endorectal MRI before salvage radiotherapy were selected. Spatial coordinates of the relapses were assessed using two reference points: the inferior border of the pubic symphysis (point 1) and the urethro-vesical anastomosis (point 2). Every lesion on MRI was delineated on the planning computed tomography and center of mass coordinates were plotted in two separate diagrams (along the x, y, and z axes) with the urethro-vesical anastomosis as the coordinate origin. An "ideal" CTV was constructed, centered at a point defined by the mathematical means of each of the three coordinates with dimensions defined as twice 2 standard deviations in each of the three axes. The dosimetric impact of the new CTV definition was evaluated in six adjuvantly treated patients.


RESULTS
The ideal CTV center of mass was located at coordinates 0 (x), -5 (y), and -3 (z) mm with SDs of 6 (x), 6 (y), and 9 (z) mm, respectively. The CTV size was 24 (x) x 24 (y) x 36 (z) mm. Significant rectal sparing was observed with the new CTV.


CONCLUSIONS
A CTV with an approximately cylindrical shape (approximately 4 x 3 cm) centered 5 mm posterior and 3 mm inferior to the urethro-vesical anastomosis was defined. Such CTV may reduce the irradiation of normal nontarget tissue in the pelvis potentially improving treatment tolerance.
Miralbell
Raymond
R
Division de Radio-oncologie, Hôpitaux Universitares, Genève, Switzerland. Raymond.Miralbell@hcuge.ch
Vees
Hansjörg
H
Lozano
Joan
J
Khan
Haleem
H
Mollà
Meritxell
M
Hidalgo
Alberto
A
Linero
Dolors
D
Rouzaud
Michel
M
D000328:Adult; D000368:Aged; D017408:Guidelines as Topic; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000097:blood / Q000175:diagnosis* / Q000532:radiotherapy; D017430:Prostate-Specific Antigen / Q000097:blood; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy / Q000601:surgery; D019736:Prostheses and Implants; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D018714:Radiotherapy, Adjuvant / Q000592:standards; D016879:Salvage Therapy / Q000592:standards*; D014057:Tomography, X-Ray Computed
D017430:Prostate-Specific Antigen