Comparison of CT and positron emission tomography/CT coregistered images in planning radical radiotherapy in patients with non‐small‐cell lung cancer

Abstract

Imaging with F-18 fluorodeoxyglucose positron emission tomography (PET) significantly improves lung cancer staging, especially when PET and CT information are combined. We describe a method for obtaining CT and PET images at separate acquisitions, which allows coregistration and incorporation of PET information into the radiotherapy (RT) planning process for non-small-cell lung cancer. The influence of PET information on RT planning was analysed for 10 consecutive patients. Computed tomography and PET images were acquired with the patient in an immobilization device, in the treatment position. Using specially written software, PET and CT data were coregistered using fiducial markers and imported into our RT planning system (Cadplan version 6). Treatment plans were prepared with and without access to PET/CT coregistered images and then compared. PET influenced the treatment plan in all cases. In three cases, geographic misses (gross tumour outside planning target volume) would have occurred had PET not been used. In a further three cases, better planning target volume marginal coverage was achieved with PET. In four patients, three with atelectasis, there were significant reductions in V20 (percentage of the total lung volume receiving 20 Gy or more). Use of coregistered PET/CT images significantly altered treatment plans in a majority of cases. This method could be used in routine practice at centres without access to a combined PET/CT scanner .

Quantification of Tumor Volume Changes During Radiotherapy for Non–Small-Cell Lung Cancer

“…In such cases, the GTV can be found to have originally been overestimated or, even, underestimated. This has been demonstrated in studies using positron emission tomography scans to distinguish tumor from atelectasis, often resulting in changes in the CT-generated GTVs (21,22). In cases of overestimation of the GTV, the volumes can be better defined with a repeat scan after a few weeks of treatment, yielding a more favorable normal tissue toxicity profile.…”

Reproducibility of “Intelligent” Contouring of Gross Tumor Volume in Non–Small-Cell Lung Cancer on PET/CT Images Using a Standardized Visual Method

“…The reasons for avoiding purely automated contouring were described in a recent article (22). Our contouring methodology has gradually been refined after the earlier experience with coregistered PET and CT images (23,24) and experience with contouring using CT alone (20). When our CT contouring method was adapted for use with PET/ CT, it became the responsibility of a dual-trained PET physician/diagnostic radiologist to determine which structures were malignant before contouring.…”

18F-Fluorodeoxyglucose Positron Emission Tomography-Based Assessment of Local Failure Patterns in Non–Small-Cell Lung Cancer Treated With Definitive Radiotherapy

“…Information from 18 FDG-PET scans can lead to altered staging and target volumes either by upstaging, because of previously undetected nodal disease, or downstaging, because of atelectasis or previously suspicious nodal disease found to be metabolically insignificant (8,9,(16)(17)(18)(19)(20). The effect of pre-RT 18 FDG-PET data incorporation into treatment planning on the patterns of local failure has been insufficiently investigated.…”