Incremental clinical value of a dedicated RT planning FDG PET-CT over staging PET-CT in non-small cell lung cancer

Objectives To evaluate whether a FDG PET scan performed for radiotherapy (RT) planning purpose can detect disease progression, compared with the staging FDG PET.

Methods Thirteen patients (pts) underwent a planning PET-CT for curative RT ("RT-PET") within eight weeks (mean: 28.7 ± 12 days, range:7-54 days) of a staging PET-CT ("Stage-PET") for newly diagnosed untreated NSCLC between 10/2007 and 1/2009. All studies were acquired on a Philips GXL PET-CT using the same protocols, except RT-PET is acquired on a RT flat bed insert in a simulated traetment position. The images were interpreted by consensus readings of two NM physicians: location/number, visual grading (0-4: 3 > liver, 4 > brain), max Transverse diameter ("Max D") (the tumour margin is delineated by a SUV threshhold of 2.5) and max SUV of each lesion. Progressive disease (PD) is defined as >10% increase in max D.

Results RT-PET detected PD (primary or nodal) or new metastases in 8 pts (61%) (mean interval: 30.2 ± 14 days, range: 7-54 days). For primary tumour, RT-PET detected PD in 5 pts (12-32% increase in max D and 12-39% increase in max SUV) and RT-CT detected PD in 3 pts (11-21% increase in max D, paired t test: p = 0.19). Stage-PET detected 28 mediastinal or hilar nodes. RT-PET detected PD in 11of these lesions in 4 pts (31%) and CT detected similar progression in 8 lesions in 2 pts. RT-PET detected 10 new lesions (grade 3 or above and/or SUV >2.5) in 3 pts (23%) resulting in upstaging to N3 in 2 pts (supraclavicular and hilar nodes) and M1 in 1 pt (bone).

Conclusions A dedicated RT planning PET-CT has the potential to detect disease progression and impact on RT in a large number of patients.