Automated functional image-guided radiation treatment planning for rectal cancer.
OBJECTIVE
Computer tomography-based (CT-based) tumor-volume definition is time consuming and is subject to clinical interpretation. CT is not accessible for standardized algorithms for the purpose of treatment-volume planning. We have evaluated the accuracy of target-volume definition based on the positron emission tomography (PET) data from an integrated PET/CT system with 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) for standardized target-volume delineation.


METHODS
Eleven patients with rectal cancer who were undergoing preoperative radiation therapy (RT) were studied. A standardized region-growing algorithm was tested to replace the CT-derived gross tumor volume by the PET-derived gross tumor volume (PET-GTV) or the biologic target volume (BTV). A software tool was developed to automatically delineate the appropriate tumor volume as defined by the FDG signal, the PET-GTV, and the planning target volume (PTV). The PET-derived volumes were compared with the target volumes from CT.


RESULTS
The BTV defined for appropriate GTV assessment was set at a single peak threshold of 40% of the signal of interest. Immediate treatment volume definition based on the choice of a single-tumor volume-derived PET-voxel resulted in a tumor volume that strongly correlated with the CT-derived GTV (r(2) = 0.84; p < 0.01) and the volume as assessed on subsequent anatomic-pathologic analysis (r(2) = 0.77; p < 0.01). In providing sufficient extension margins from the CT-derived GTV and the PET-derived GTV, to PTV, respectively, the correlation of the CT-derived and PET-derived PTV was sufficiently accurate for PTV definition for external-beam therapy (r(2) = 0.96; p < 0.01).


CONCLUSIONS
Automated segmentation of the PET signal from rectal cancer may allow immediate and sufficiently accurate definition of a preliminary working PTV for preoperative RT. If required, correction for anatomic precision and geometric resolution may be applied in a second step. Computed PET-based target-volume definition could be useful for the definition of standardized simultaneous internal-boost volumes for intensity-modulated radiation therapy (IMRT) based on biologic target volumes.
Ciernik
Ilja Frank
IF
Department of Radiation Oncology, Zurich University Hospital, Zurich, Switzerland. ciernik@usz.ch
Huser
Marius
M
Burger
Cyrill
C
Davis
J Bernard
JB
Szekely
Gabor
G
D019788:Fluorodeoxyglucose F18; D006801:Humans; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D014057:Tomography, X-Ray Computed / Q000379:methods*
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18