Background: Tl-201 brain imaging has been demonstrated to correlate to tumour grade and type. Tl-201 uptake is often expressed as a ratio relative to normal brain. Using a quantitative SPECT reconstruction algorithm previously reported (1) but now applied to thallium, we can calculate actual thallium uptake (ATU) in kBq/ml and derive an SUV (corrected for weight and dose).

Aim: To determine whether ATU and SUV correlates with standard ratio measurements

Patients and method: A total of 40 scans in 23 patients were obtained. All patients had a scan in the immediate post operative time period. 12 patients had at least 1 further scan. Uptake was measured using “PETVOI” software and an ATU and SUV calculated for each patient. Follow-up was obtained out to 12-31 months or until death.

Results: Of the 23 patients studied, 10 are still alive. There was a high correlation between ratio values and both the ATU and SUV (p<0.0001). The mean baseline SUV for the survivors is 1.8 (range 1-3.5) vs 3.0 (range 1-7.8) for the non-survivors (NS). Where the initial ATU was < 1.5kBq/ml, 7/8 survived >12 months (88%). Where the initial ATU was > 1.5kBq/ml, only 5/15 survived >12 months (33%) p=0.072.

Conclusion: The ATU and SUV highly correlate with standard ratio values. A high value of these indices is associated with poorer outcomes.

(1)K Willowson, DL Bailey and C Baldock (2008) Quantitative SPECT reconstructions using CT-derived corrections Phys Med Biol 53:3099-3112