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

¹ Northern Ireland Regional Medical Physics Agency, Musgrave and Clark House, Grosvenor Road, Belfast BT12 6BA, UK, ² Northern Ireland Regional Medical Physics Agency and ³ Clinical Oncology, Belvoir Park Hospital, Belfast BT8 8JR, UK, ⁴ U650 INSERM, LaTIM, Brest, France and ⁵ Department of Radiology, Royal Group of Hospitals, Grosvenor Road, Belfast BT12 6BA, UK

View larger version (94K): [in a new window]   Figure 1. Flat-bed insert on scanner couch.

View larger version (107K): [in a new window]   Figure 2. Patient in treatment position passing through scanner.

View larger version (39K): [in a new window]   Figure 3. PET images in a patient with right hilar cancer illustrating problems with accurate delineation of target volumes based on thresholding of PET images. (A) PET threshold is set at 40% of maximum standard uptake value (SUV) of tumour. (B) PET threshold is set at 30% of maximum SUV. If delineating this tumour using PET alone, different threshold settings would result in different target volumes. Reprinted with permission of the Society of Nuclear Medicine from: Bradley JD, Perez CA, et al. Implementing biologic target volumes in radiation treatment planning for non-small cell lung cancer. J Nucl Med 2004;45:96S–101S.

View larger version (57K): [in a new window]   Figure 4. Wire diagrams showing planning target volume (PTV) delineated from CT (yellow) and from CT + PET (red) for one non-small cell lung cancer patient. Involved paratracheal lymph nodes were detected on PET scan, which were subsequently incorporated into the patient PTV. Reprinted with permission of Elsevier from: Erdi YE, Rosenzweig K, Erdi AK, et al. Radiotherapy treatment planning for patients with non-small cell lung cancer using positron emission tomography (PET). Radiother Oncol 2002;62:51–60.

View larger version (63K): [in a new window]   Figure 5. Problems with accurate delineation of target volumes as a result of differences in the state of respiration between emission and transmission maps (note changes in the tumour in the mediastinum as well as the artefact areas). Left: attenuation correction using a respiration average transmission map with radioactive rod sources. Centre: attenuation correction using a CT map acquired at end inspiration. Right: attenuation correction using a CT map acquired at end expiration or under free breathing. Adapted from: Visvikis D, Costa DC, Croasdale I, et al. CT-based attenuation correction in the calculation of semi-quantitative indices of [18F]FDG uptake in PET. Eur J Nucl Med Mol Imaging. 2003;30:344–53. Reprinted with kind permission of Springer Science and Business Media.

View larger version (35K): [in a new window]   Figure 6. Problems with accurate delineation of target volumes as a result of respiratory motion during emission acquisition. (a) Tumour extent during a respiratory average frame. (b) Tumour extent in a respiratory-gated frame. (c) Planning target volume (PTV) from the gated and non-gated PET frames. Reprinted with permission of the Society of Nuclear Medicine from: Nehmeh S, Erdi Y, Ling CC, et al. Effect of respiratory gating on quantifying PET images of lung cancer. J Nucl Med 2002;43:876–81.

View larger version (19K): [in a new window]   Figure 7. Demonstration of image quality degradation as a function of image statistics between respiration average and respiration-gated frames at the level of the lung. Simulated 22 mm (left lung) and 16 mm (right lung) lesions at different levels of the pulmonary field are included. Respiration average frame: (a) 30M total coincidences and (b) 20M total coincidences. Corresponding respiration-gated frame: (a) 10M, (b) 6M, (c) 4M and (d) 2M total coincidences.

View larger version (128K): [in a new window]   Figure 8. BIOPAC trigger unit and strain gauge.