In somatostatin receptor-targeted therapy, renal toxicity is an expected side effect, and therefore pretherapeutic dosimetry based on a measured kinetics is preferable. In contrast, a convenient one single-time-point scan might also reveal relevant information on expected dose to organs. However, very early time points might not reflect the true retention by the renal cortex and therefore be of limited value to predict dose for the long-lived 177Lu.
PATIENTS AND METHODS:
Dosimetry with 111In-octreotide was performed in 24 patients, and the number of disintegrations (ND) were calculated for 177Lu. Uptake values for each time point were correlated with ND.
The fitting algorithm was best with biexponential equations in 18 patients. Mean biologic half-life of the alpha component was 6 hours (+/-12 hours) and for the beta component 82 hours (+/-38 hours). For the early time points, correlation with ND was generally poor. For later time points, correlation increased markedly after 4 hours (4 hours: r = 0.83, 72 hours: r = 0.93) and were also capable of predicting dosimetry to some extent.
In conclusion, thorough quantification of the 4 hours single-time-point scans seems to be enough to predict the expected renal dose for radionuclide therapies to some degree.