Development and validation of a variance model for dynamic PET: uses in fitting kinetic data and optimizing the injected activity.

The precision of biological parameter estimates derived from dynamic PET data can be limited by the number of acquired coincidence events (prompts and randoms). These numbers are affected by the injected activity (A(0)). The benefits of optimizing A(0) were assessed using a new model of data variance which is formulated as a function of A(0). Seven cancer patients underwent dynamic [(15)O]H(2)O PET scans (32 scans) using a Biograph PET-CT scanner (Siemens), with A(0) varied (142-839 MBq). These data were combined with simulations to (1) determine the accuracy of the new variance model, (2) estimate the improvements in parameter estimate precision gained by optimizing A(0), and (3) examine changes in precision for different size regions of interest (ROIs). The new variance model provided a good estimate of the relative variance in dynamic PET data across a wide range of A(0)s and time frames for FBP reconstruction. Patient data showed that relative changes in estimate precision with A(0) were in reasonable agreement with the changes predicted by the model: Pearson's correlation coefficients were 0.73 and 0.62 for perfusion (F) and the volume of distribution (V(T)), respectively. The between-scan variability in the parameter estimates agreed with the estimated precision for small ROIs (<5 mL). An A(0) of 500-700 MBq was near optimal for estimating F and V(T) from abdominal [(15)O]H(2)O scans on this scanner. This optimization improved the precision of parameter estimates for small ROIs (<5 mL), with an injection of 600 MBq reducing the standard error on F by a factor of 1.13 as compared to the injection of 250 MBq, but by the more modest factor of 1.03 as compared to A(0) = 400 MBq.

No relationship between 18F-fluorodeoxyglucose positron emission tomography and expression of Glut-1 and -3 and hexokinase I and II in high-grade glioma.

The purpose of this study was to compare glucose metabolism, measured using 18F-fluorodeoxyglucose positron emission tomography ([18F]FDG-PET), with the expression of Glut-1 and -3 and hexokinase I (Hex I) and II in high-grade glioma. The retrospective study involved 27 patients with WHO classification grade III and IV glioma, with either newly diagnosed or recurrent tumours. Patients underwent dynamic and static [18F]FDG-PET to glucose metabolic rate (MRGlu) and standardised uptake value (SUV), respectively. Tumour biopsies were obtained and stained using immunohistochemistry for the expression of Glut-1, -3, Hex I and II. Relationships between variables were studied using Spearman's rank correlation test. Results showed that the expression of Glut-1, Glut-3, Hex I and Hex II varied between and within the tumour samples. The mean of MRGlu was 0.2 (range 0.09-0.25) micromol/min/ml and that of SUV was 4.2 (range 3.2-5.2). There were no significant relationships among the tumour expression of any of the proteins studied with either MRGlu or SUV (p>0.21 for all). In conclusion, the lack of relationship between the immunohistochemical expression of Glut-1, -3, Hex I or II and glucose metabolism measured using [18F]FDG-PET in patients with high-grade glioma may be due to the tissue heterogeneity and presence of necrosis in high-grade tumours.

The use of CT-MR image registration to define target volumes in pelvic radiotherapy in the presence of bilateral hip replacements.

Increasing numbers of patients with hip replacements are presenting for pelvic radiotherapy, which is usually planned using CT images. Image artefacts caused by the presence of metallic implants tend not to be severe for single hip replacements and allow for adequate definition of target volumes. When bilateral hip replacements are present, the image artefacts can render CT images useless for target definition, particularly for tumours of the prostate and bladder. MR images are not susceptible to such severe artefacts. This note describes a small series of patients with bilateral hip replacements on whom CT-MR image registration has been used to successfully define adequate target volumes.

Effective treatment of anal cancer in the elderly with low-dose chemoradiotherapy.

Chemoradiotherapy (CRT) is accepted as the standard initial treatment for squamous cell anal cancer. However, frail elderly patients cannot always tolerate full-dose CRT. This paper reports the results of a modified regimen for this group of patients. In all, 16 patients with biopsy-proven squamous cell carcinoma of the anal canal or margin and performance status or co-morbidity precluding the use of full-dose CRT were included in this protocol. The median age was 81 (range 77-91). Patients received a dose of 30 Gy to the gross tumour volume plus 3 cm margin in all directions. Concurrent chemotherapy comprised 5-fluorouracil 600 mg m(-2) given over 24 h on days 1-4 of radiotherapy. The treatment was well tolerated. All 16 patients completed treatment as planned. Only one patient experienced any grade 3 toxicity (skin). The local control at a median follow-up of 16 months was 73% (13 out of 16). The overall survival was 69% and disease-specific survival 86%. This is a well-tolerated regimen for elderly/poor performance patients with anal cancer, which can achieve high rates of local control and survival. Longer follow-up will determine whether these encouraging results are maintained.