Incorporating quantitative single photon emission computed tomography into radiation therapy treatment planning for lung cancer: impact of attenuation and scatter correction on the single photon emission computed tomography-weighted mean dose and functional lung segmentation.

PURPOSE: To assess the impact of attenuation and scatter corrections on the calculation of single photon emission computed tomography (SPECT)-weighted mean dose (SWMD) and functional volume segmentation as applied to radiation therapy treatment planning for lung cancer. METHODS AND MATERIALS: Nine patients with lung cancer underwent a SPECT lung perfusion scan. For each scan, four image sets were reconstructed using the ordered subsets expectation maximization method with attenuation and scatter corrections ranging from none to a most comprehensive combination of attenuation corrections and direct scatter modeling. Functional volumes were segmented in each reconstructed image using 10%, 20%, …, 90% of maximum SPECT intensity as a threshold. Systematic effects of SPECT reconstruction methods on treatment planning using functional volume were studied by calculating size and spatial agreements of functional volumes, and V(20) for functional volume from actual treatment plans. The SWMD was calculated for radiation beams with a variety of possible gantry angles and field sizes. RESULTS: Functional volume segmentation is sensitive to the particular method of SPECT reconstruction used. Large variations in functional volumes, as high as >50%, were observed in SPECT images reconstructed with different attenuation/scatter corrections. However, SWMD was less sensitive to the type of scatter corrections. SWMD was consistent within 2% for all reconstructions as long as computed tomography-based attenuation correction was used. CONCLUSION: When using perfusion SPECT images during treatment planning optimization/evaluation, the SWMD may be the preferred figure of merit, as it is less affected by reconstruction technique, compared with threshold-based functional volume segmentation.

Impact of F-18 fluorodeoxyglucose positron emission tomography-computed tomography on oncologic patient management: first 2 years' experience at a single Canadian cancer center.

PURPOSE: The purpose of this study was to assess the influence of positron emission tomography-computed tomography (PET-CT) results on patient management from a single Canadian oncology center during its first 2 years of operation. METHODS: A total of 3,779 consecutive patients, 18 years of age and older, who were referred for PET-CT imaging at the British Columbia Cancer Agency between July 1, 2005 and June 30, 2007, were included in this analysis. Results were tabulated from a standard questionnaire, which was given to referring physicians following completion of their patient's PET-CT study. RESULTS: From July 1, 2005 to June 30, 2007, 3,779 consecutive fluoro-2-deoxyglucose PET-CT examinations were performed in patients aged 18 years or older. A total of 3,429 referring-physician surveys (90.7%) were returned. The results of the PET-CT study resulted in a change in treatment decision in 49.8% of the studies and resulted in improved decision making in 83.2% of the studies. CONCLUSION: This series demonstrated that the results from PET-CT studies performed at a single Canadian oncology center during the first 2 years of its operation altered patient management in 50% of cases and resulted in improved decision making in the majority of cases.

The Role of 18-FDG Positron Emission Tomography (FDG-PET) in Detecting Post- Radiotherapy Loco Regional Relapse/Residual Disease in Nasopharyngeal Cancer.

BACKGROUND: Post-radiotherapy nasopharyngeal changes represent a diagnostic dilemma. Early detection of persistent or recurrent disease may be translated to better cure rate if salvage therapy is implemented. Neither clinical exam nor current radiological anatomical studies (CT/MRI) can differentiate between benign post therapy changes and recurrence. PET scan is a functional study capable of identifying viable tumors as areas of increased radiotracer uptake. METHODS: Fifty-five patients underwent 18-FDG PET scans post radiation therapy for nasopharyngeal carcinoma at King Faisal Specialist Hospital and Research Centre. We compared the 18-FDG PET scan with the clinical, radiological and pathological findings. RESULTS: Clinical examination and CT of the head and neck showed post-treatment abnormality in the nasopharynx in 40 patients. Among these, 28 patients had asymmetry in the CT scan. Three out of the 28 patients had positive PET scan. Out of the 12 patients with positive primary disease in the CT scan, 3 had negative PET scan which was also confirmed by biopsy in 2 patients. Eleven patients had positive PET scan in the primary site; this was pathologically confirmed to be recurrent disease in 5 patients. In 2 patients repeat PET scan was converted to negative. The remaining 4 patients did not have biopsy due to the presence of concurrent distant disease. None of the patients with negative PET scan in the neck exhibit recurrence or persistent neck disease to the day of reporting the study. PET scan showed persistent higher sensitivity, specificity, positive and negative predictive values at both the primary site and the neck region than the CT did. CONCLUSION: PET scan is a useful tool in differentiating between post radiotherapy fibrosis and recurrent nasopharyngeal cancer. KEY WORDS: Nasopharyngeal cancer - FDG/PET - Post therapy changes.

Problems created in attenuation-corrected SPECT images by artifacts in attenuation maps: a simulation study.

UNLABELLED: The importance of accurate attenuation correction, especially for imaging of the thorax region, is widely acknowledged. Appropriate compensation methods have been developed and introduced into clinical practice. Most of these methods use attenuation maps obtained using various transmission scanning systems. However, when maps are inaccurate, the correction procedure may introduce artifacts into the final images that can be difficult to identify and might inadvertently alter diagnosis and study outcome. As a result, attenuation correction is often avoided in clinical practice. Our objective was to examine issues related to the quality of attenuation maps and the effects that map artifacts may have on attenuation-corrected emission images. METHODS: The topics that are investigated include the problem of low transmission counts, cross-talk contributions from the emission isotope, truncation of the transmission data, and methods of map reconstruction and segmentation. Examples of patient studies displaying specific problems guided our investigations, but, because truth in these studies is seldom known, analytic and Monte Carlo-simulated data were used in the analysis. Attenuation maps and final emission images were visually checked for artifacts and for the presence of perfusion defects. In addition, quantitative evaluation of map uniformity, defect visibility, and size variation was performed. RESULTS: The statistical paired-sample t test showed significant (P < 0.05) improvement of relative SD for attenuation maps reconstructed with iterative methods as compared with filtered backprojection and for maps created with higher photon fluxes. When maps with artifacts were used to correct emission data, an increase in myocardial infarct size and creation of false heart defects were observed. CONCLUSION: Our study strongly recommends that at least a visual inspection of the quality of attenuation maps be performed before their use in compensation procedures. To improve image quality, remove artifacts, and increase diagnostic confidence, attenuation maps used in the correction procedure must be accurate and free of artifacts.