Objectives: To develop and validate a method for quantitative ²⁰¹Tl SPECT data based on corrections derived from X-ray CT data, and to apply the method in the clinic for quantitative determination of recurrence of brain tumours.

Method: A previously developed method for achieving quantitative SPECT with ^99mTc based on corrections derived from x-ray CT data was extended to apply to ²⁰¹Tl. Experimental validation was performed on a cylindrical phantom by comparing known injected activity and measured concentration to quantitative calculations. Further evaluation was performed on a RSI Striatal Brain Phantom containing three “lesions” with activity to background ratios of 1:1, 1.5:1 and 2:1. The method was subsequently applied to a series of scans from patients with suspected recurrence of brain tumours (principally glioma) to determine an SUV-like measure (Standardised Uptake Value).

Results: The total activity and concentration in the phantom were calculated to within 3% and 1% of the true values, respectively. The calculated values for the concentration of activity in the background and corresponding lesions of the brain phantom (in increasing ratios) were found to be within 2%, 10%, 1% and 2%, respectively, of the true concentrations. Patient studies showed that an initial SUV greater than 1.5 corresponded to a 56% mortality rate in the first 12 months, as opposed to a 14% mortality rate for those with a SUV less than 1.5.

Conclusion: The quantitative technique produces accurate results for the radionuclide ²⁰¹Tl. Initial investigation in clinical brain SPECT suggests correlation between quantitative uptake and survival.