title: 3D-segmentation of the 18F-choline PET signal for target volume definition in radiation therapy of the prostate.
abstract: Volumetric assessment of PET signals becomes increasingly relevant for radiotherapy (RT) planning. Here, we investigate the utility of 18F-choline PET signals to serve as a structure for semi-automatic segmentation for forward treatment planning of prostate cancer. 18F-choline PET and CT scans of ten patients with histologically proven prostate cancer without extracapsular growth were acquired using a combined PET/CT scanner. Target volumes were manually delineated on CT images using standard software. Volumes were also obtained from 18F-choline PET images using an asymmetrical segmentation algorithm. PTVs were derived from CT 18F-choline PET based clinical target volumes (CTVs) by automatic expansion and comparative planning was performed. As a read-out for dose given to non-target structures, dose to the rectal wall was assessed. Planning target volumes (PTVs) derived from CT and 18F-choline PET yielded comparable results. Optimal matching of CT and 18F-choline PET derived volumes in the lateral and cranial-caudal directions was obtained using a background-subtracted signal thresholds of 23.0+/-2.6%. In antero-posterior direction, where adaptation compensating for rectal signal overflow was required, optimal matching was achieved with a threshold of 49.5+/-4.6%. 3D-conformal planning with CT or 18F-choline PET resulted in comparable doses to the rectal wall. Choline PET signals of the prostate provide adequate spatial information amendable to standardized asymmetrical region growing algorithms for PET-based target volume definition for external beam RT.
authors.affiliation: Center for Clinical Research, Zurich University Hospital, Zurich, Switzerland. ciernik@iosi.ch
authors.forename: I Frank
authors.initials: IF
authors.lastname: Ciernik
authors.forename: Derek W
authors.initials: DW
authors.lastname: Brown
authors.forename: Daniel
authors.initials: D
authors.lastname: Schmid
authors.forename: Thomas
authors.initials: T
authors.lastname: Hany
authors.forename: Peter
authors.initials: P
authors.lastname: Egli
authors.forename: J Bernard
authors.initials: JB
authors.lastname: Davis
mesh_terms: D002794:Choline / Q000031:analogs & derivatives*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D049268:Positron-Emission Tomography; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*
chemical_list: C516370:fluoromethylcholine; D002794:Choline