Impact of Computed Tomography and 18F-Deoxyglucose-Hybrid Positron Emission Tomography Image Fusion on Conformal Radiotherapy in Non-Small Cell Lung Cancer
Presenter: E. Deniaud-Alexandre.
Presenter's Affiliation: Tenon Hospital, Paris, France
Type of Session: Scientific
- PET scans offer quantitative data regarding the glucose utilization of both tumor and normal tissue.
- PET scans have become commonplace in the staging of non small cell lung cancer (NSCLC)
- Recently, computer software has enabled the fusion of PET images with anatomic CT images, in the hopes of improving the accuracy of staging NSCLC.
- The authors presented retrospective research on the value of fused PET/CT images used during radiation treatment planning.
- Between March 2000 and March 2004, 101 patients with localized NSCLC underwent both PET and CT imaging.
- Images were co-registered using five feducial markers.
- Target volume delineation was initially performed on the CT images, then the corresponding PET data were used as an overlay on to the CT data for further target delineation.
- Mean age was 64.5 years old.
- PET detected 8 patients with previously undetected metastases, and 1 patient with thoracic disease too extensive for radical therapy.
- Amongst the 92 patients treated with curative intent, 5 were planned as pre-operative cases and the other 87 as primary radiotherapy cases (with or without chemotherapy).
- The radiation oncologist’s determination of the gross tumor volume (GTV) increased after PET/CT fusion in 26% of cases, and decreased in 23% of cases.
- For the 81 patients who received >60 Gy, the total lung volume getting > 20 Gy (VL20) increased in 18.5% and decreased in 27% of the patients.
- For the 81 patients who received >60 Gy, the total heart volume getting > 36 Gy (VL36) increased in 10% and decreased in 17% of the patients.
- Multivariate analysis demonstrated that the only factor which was significantly related to modifying the GTV was the presence of atelectasis (p=0.0002).
- Integrated hybrid PET/CT in the treatment position with coregistered images has an impact on radiation treatment planning.
- The impact was major for tumors with atelectasis.
- The impact on treatment outcomes remains to be demonstrated.
- Based on this research, their institution purchased a dedicated PET/CT in January 2005.
The authors presented a retrospective study of 101 patients in an effort to determine how the use of fused PET/CT images would affect radiation treatment planning. This is an interesting piece of research, but their results would be more impressive if they had also calculated how the radiation oncologists would have changed the GTV, VL20, and VL36 after examining a PET scan without the co-registered image fusion. One could speculate that just using a PET scan without co-registration may alter target delineation above CT imaging alone, and this research would be more powerful if we learned how much the fusion process actually gained us above simply examining both scans side by side. The authors are correct in their conclusion that the impact on treatment outcomes remains yet to be determined following the application of this new technology. The advent of dedicated PET/CT scans may improve the accuracy of metabolic imaging, and this has been suggested in a randomized trial. As this modality becomes more commonplace, it will eventually become clear how its use can potentially improve outcomes in this disease.