A prospective study to evaluate the impact of FDG-PET on CT-based radiotherapy treatment planning for oesophageal cancer.
OBJECTIVE
This prospective study sought to determine how the use of combined PET/CT for radiotherapy treatment planning of oesophageal cancer would alter the delineation of tumour volumes compared to CT alone if PET/CT is assumed to more accurately represent true disease extent.


METHODS
All patients underwent FDG-PET/CT scanning in the radiotherapy treatment position. For each patient, two separate gross tumour volumes (GTV) were defined, one based on CT images alone (GTV-CT) and another based on combined PET/CT data (GTV-PET). Corresponding planning target volumes (PTV) were generated, and separate treatment plans were then produced. For each patient, volumetric analysis of GTV-CT, PTV-CT and GTV-PET was performed to quantify the proportion of PET-avid disease that was not included in the GTV and PTV (geographic miss) if CT data alone were used for radiotherapy planning. Assessment of the cranial and caudal extent of the primary oesophageal tumour as defined by CT alone vs PET/CT was also compared.


RESULTS
The addition of PET information altered the clinical stage in 8 of 21 eligible patients enrolled on the study (38%); 4 patients had distant metastatic disease and 4 had unsuspected regional nodal disease. Sixteen patients proceeded to the radiotherapy planning phase of the study and received definitive chemoradiation planned with the PET/CT data set. The GTV based on CT information alone excluded PET-avid disease in 11 patients (69%), and in five patients (31%) this would have resulted in a geographic miss of gross tumour. The discordance between CT and PET/CT was due mainly to differences in defining the longitudinal extent of disease in the oesophagus. The cranial extent of the primary tumour as defined by CT vs PET/CT differed in 75% of cases, while the caudal extent differed in 81%.


CONCLUSIONS
This study demonstrates that if combined PET/CT is used for radiotherapy treatment planning, there may be alterations to the delineation of tumour volumes when compared to CT alone, with the potential to avoid a geographic miss of tumour.
Leong
Trevor
T
Department of Radiation Oncology, Peter MacCallum Cancer Centre, and Department of Medicine, University of Melbourne, Vic., Australia. trevor.leong@petermac.org
Everitt
Craig
C
Yuen
Kally
K
Condron
Sara
S
Hui
Andrew
A
Ngan
Samuel Y K
SY
Pitman
Alexander
A
Lau
Eddie W F
EW
MacManus
Michael
M
Binns
David
D
Ackerly
Trevor
T
Hicks
Rodney J
RJ
D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D049268:Positron-Emission Tomography / Q000379:methods; D011446:Prospective Studies; D011874:Radiometry / Q000379:methods*; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000639:trends*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18