Addition of 18F-FDG-PET scans to radiotherapy planning of thoracic lymphoma.

BACKGROUND AND PURPOSE: FDG-PET possesses greater sensitivity and accuracy than computed tomography (CT) in detecting diseased lymph nodes. Though the FDG-PET scans are acquired for similar diagnostic reasons as CT, they are not used in the radiotherapy (RT) planning process. Successful tumourcidal dose is usually delivered but large volumes of normal and non-malignant tissues are irradiated due to the nature of lymphoma and also to the subjectivity of the field determining process. This study tries to lessen the subjectivity of the field determining process by the addition of currently acquired PET to the conventional thoracic lymphoma RT. The differences between retrospectively delineated volumes from CT and FDG-PET were compared and the effect of this additional information was evaluated. MATERIALS AND METHODS: Seventeen FDG-PET scans were registered to corresponding CT scans using rigid-body registration with negligible intra-observer variability. Comparisons were made between the volumes, lateral extensions and the most inferior point of the delineated gross tumour volumes (GTVs). RESULTS: For 1/17 patient data, no diseased volumes were delineated and in 6/17, no volumes were delineated on PET and yet in CT, masses up to 367.2 cm3 were outlined. From the 10 positive-CT and PET data, the GTV(PET) were smaller than GTV(CT) in six cases. Greater than 3.0 cm lateral disease extension differences were observed in 4/10 cases. Inferior tumour extents were confirmed in 6/10 cases whereas in 2/10 patients GTV(CT) was greater than 12.0 cm inferior compared to GTV(PET). CONCLUSIONS: FDG-PET data can be introduced to current thoracic lymphoma RT planning protocol with minimal intervention and changes. The subjectivity in the RT planning of thoracic lymphoma would be decreased with the addition of currently acquired FDG-PET data.