The potential advantages of (18)FDG PET/CT-based target volume delineation in radiotherapy planning of head and neck cancer.
OBJECTIVE
This study investigated two fixed threshold methods to delineate the target volume using (18)FDG PET/CT before and during a course of radical radiotherapy in locally advanced squamous cell carcinoma of the head and neck.


METHODS
Patients were enrolled into the study between March 2006 and May 2008. (18)FDG PET/CT scans were carried out 72h prior to the start of radiotherapy and then at 10, 44 and 66Gy. Functional volumes were delineated according to the SUV Cut Off (SUVCO) (2.5, 3.0, 3.5, and 4.0bwg/ml) and percentage of the SUVmax (30%, 35%, 40%, 45%, and 50%) thresholds. The background (18)FDG uptake and the SUVmax within the volumes were also assessed.


RESULTS
Primary and lymph node volumes for the eight patients significantly reduced with each increase in the delineation threshold (for example 2.5-3.0bwg/ml SUVCO) compared to the baseline threshold at each imaging point. There was a significant reduction in the volume (p⩽0.0001-0.01) after 36Gy compared to the 0Gy by the SUVCO method. There was a negative correlation between the SUVmax within the primary and lymph node volumes and delivered radiation dose (p⩽0.0001-0.011) but no difference in the SUV within the background reference region. The volumes delineated by the PTSUVmax method increased with the increase in the delivered radiation dose after 36Gy because the SUVmax within the region of interest used to define the edge of the volume was equal or less than the background (18)FDG uptake and the software was unable to effectively differentiate between tumour and background uptake.


CONCLUSIONS
The changes in the target volumes delineated by the SUVCO method were less susceptible to background (18)FDG uptake compared to those delineated by the PTSUVmax and may be more helpful in radiotherapy planning. The best method and threshold have still to be determined within institutions, both nationally and internationally.
Moule
Russell N
RN
University College Hospitals NHS Foundation Trust, London, UK. rn.moule@virgin.net
Kayani
Irfan
I
Moinuddin
Syed A
SA
Meer
Khalda
K
Lemon
Catherine
C
Goodchild
Kathleen
K
Saunders
Michele I
MI
D000368:Aged; D004307:Dose-Response Relationship, Radiation; D019788:Fluorodeoxyglucose F18; D006258:Head and Neck Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden
D019788:Fluorodeoxyglucose F18