CT-based quantitative SPECT for the radionuclide (201)Tl: experimental validation and a standardized uptake value for brain tumour patients

We have previously reported on a method for reconstructing quantitative data from (99m)Tc single photon emission computed tomography (SPECT) images based on corrections derived from X-ray computed tomography, producing accurate results in both experimental and clinical studies. This has been extended for use with the radionuclide (201)Tl. Accuracy was evaluated with experimental phantom studies, including corrections for partial volume effects where necessary. The quantitative technique was used to derive standardized uptake values (SUVs) for (201)Tl evaluation of brain tumours. A preliminary study was performed on 26 patients using (201)Tl SPECT scans to assess residual tumour after surgery and then to monitor response to treatment, with a follow-up time of 18 months. Measures of SUV(max) were made following quantitative processing of the data and using a threshold grown volume of interest around the tumour. Phantom studies resulted in the calculation of concentration values consistently within 4% of true values. No continuous relation was found between SUV(max) (post-resection) and patient survival. Choosing an SUV(max) cut-off of 1.5 demonstrated a difference in survival between the 2 groups of patients after surgery. Patients with an SUV(max) <1.5 had a 70% survival rate over the first 10 months, compared with a 47% survival rate for those with SUV(max) >1.5. This difference did not achieve significance, most likely due to the small study numbers. By 18 months follow-up this difference had reduced, with corresponding survival rates of 40% and 27%, respectively. Although this study involves only a small cohort, it has succeeded in demonstrating the possibility of an SUV measure for SPECT to help monitor response to treatment of brain tumours and predict survival.