Monitoring and Predicting Response to Peptide Receptor Radionuclide Therapy: A Quantitative SPECT-CT Based Analysis

ABSTRACT

A standard imaging protocol for monitoring and predicting the response to Peptide Receptor Radionuclide Therapy (PRRT) has not been established yet. The aim of this study was to evaluate the response to PRRT by quantitative SPECT-CT and assess the value of SPECT-CT over routine planar scintigraphy in predicting the outcome of PRRT.

32 patients with neuroendocrine tumour, who underwent SPECT-CT imaging after the first and second course of radiolabelled DOTATOC were retrospectively analysed. The response to therapy was defined by decrease in tumour volume in CT. The uptake in planar scintigraphy was evaluated by visual assessment based on a 5-point scoring scale. From SPECT images, ratios of maximum and mean values of tumour uptake to normal liver uptake were calculated. The value of SPECT-CT over planar scintigraphy in predicting therapy response was assessed by Receiver Operating Characteristic (ROC) analysis.

Evaluation of 77 target lesions (in 32 patients) by SPECT-CT imaging, showed that the mean uptake ratio decreased from a median value of 5.66 (range 0.5 to 32.37) to 3.85 (range 0.95 to 15.75), with an overall 26 % decrease (P < 0.001). The maximum uptake ratio decreased from a median value of 7.98 (0.97 to 54.21) to 5.59 (1.95 to 29.71), with an overall 30 % decrease (P<0.002). On evaluation of 67 measurable lesions by CT (in 23 patients), the tumour volume decreased from a median value of 58.5 cm₃ (14.1 to 411.7) to 38.3 cm₃ (9.9 to 428.4) with an overall 35 % decrease (P = 0.001). The area under the ROC curve was 0.733 (95 % Confidence Interval: 0.203, 0.819) for SPECT-CT and 0.551 (95 % Confidence Interval: 0.485, 0.981) for planar scintigraphy.

Evaluation of 77 target lesions (in 32 patients) by SPECT-CT imaging, showed that the mean uptake ratio decreased from a median value of 5.66 (range 0.5 to 32.37) to 3.85 (range 0.95 to 15.75), with an overall 26 % decrease (P < 0.001). The maximum uptake ratio decreased from a median value of 7.98 (0.97 to 54.21) to 5.59 (1.95 to 29.71), with an overall 30 % decrease (P<0.002). On evaluation of 67 measurable lesions by CT (in 23 patients), the tumour volume decreased from a median value of 58.5 cm₃ (14.1 to 411.7) to 38.3 cm₃ (9.9 to 428.4) with an overall 35 % decrease (P = 0.001). The area under the ROC curve was 0.733 (95 % Confidence Interval: 0.203, 0.819) for SPECT-CT and 0.551 (95 % Confidence Interval: 0.485, 0.981) for planar scintigraphy.