Use of combined PET/CT images for radiotherapy planning: initial experiences in lung cancer

The potential role of positron emission tomography (PET) in radiotherapy still requires careful evaluation as it becomes increasingly integrated into the radiotherapy planning process. Diagnosis and subsequent radiotherapy planning based solely upon X-ray CT are known to be less sensitive and specific for disease than PET imaging in non-small cell lung cancer. The CT images may not demonstrate the true extent of intrathoracic disease. To overcome this limitation, the direct use of combined PET/CT image data in the treatment planning process has been investigated. A small pilot study of five patients was carried out at the Royal Victoria Hospital, Belfast, following the installation of a GE Discovery LS PET/CT scanner. The initial aims were to investigate the system and to make preliminary clinical evaluations. The key issues that were addressed included: verification of PET/CT alignment, patient position and reproducibility for imaging and treatment; verification of CT numbers on the PET/CT systems for dose calculation, integrity of data transfer; radiation protection of staff, protocols for target volume delineation, and the implications for physiologically-gated PET and CT acquisitions. This paper reviews our practical experience, and technical problems are described.