Effective half-life of In-111 DTPA in the CSF from whole-body Ommayogram/Cisternogram correlates with CSF leakage and blockade

Introduction: Evaluation of cerebrospinal fluid (CSF) patency is an important consideration for intrathecal therapy of patients with leptomeningeal metastasis (LM). Cisternogram is an important imaging tool to confirm of CSF leakage from subarachnoid space (SAS). In-111 DTPA is the sole FDA-approved radiopharmaceutical to image the subarachnoid space (SAS) in Cisternogram (injection via lumbar SAS) or Omayogram (ventricular injection via Omaya reservoir). This study is to study the temporal profile of In-111 DTPA in the SAA abd to correlate imaging findings in Cisternograms and Omayogram in patients with CSF flow blockade and CSF leakage.

Methods: An IRB-approved restrospective study was conducted to review consecutive cisternograms and Ommayograms from 1996 to 2005 performed with dual-head cameras. Typically, a dose of 0.5 mCi of In-111 DTPA was injected via lumbar puncture or via an implanted Ommaya reservoir over the right frontal scalp. Whole-body imaging was obtained at 4 time-points with simultaneous anterior and posterior cameras using 2 photopeaks of In-111 from the vertex down to the thighs at 0.5-2, 3-5, 18-20 and 22-26 hours. Additional static and SPECT imaging were performed. Whole-body images and static images were reviewed by 2 board-certified nuclear physicians to determine on absence of CSF block and CSF leakage. Whole-body geometric-mean (GM) images were obtained from conjugated anterior and posterior images for each time-point to account for uneven attenuation of exiting photons. The effective half-life Te of In-111 DTPA in the entire CSF / SAS was calculated from the time-activity curves of the GM serial images. Correlation was made for Te with CSF block (confirmed by MRI), CSF leak(confirmed from pledget counts and imaging), parenchymal injection in contrast to Te from patients without leak nor block.

Results: A total of 374 studies with 4-time points from BIAD dual camera were collected. From 64 patient studies without CSF leak, CSF block nor asymmetric distribution (e.g., decreased tracer over the right cerebral convexity), the average Te is 14.4 +/- 3.7 hours. Patients with confirmed CSF block have elevated Te ( above 20) while patients with CSF leakage or parenchymal extravazasion had lowered Te (below 10). Asymmetric tracer distribution over the convexity (likely related to recency of Ommaya reservior implantation). An exploratory evaluation revealed that the overal survival (OS) was not correlated to Te. While OS was shorter in patients with LM (compared with those without LM) but not different between the presence or absence of asymmetric tracer distribtution. The use of diamox also prolonged Te in patients compared to before diamox.

Conclusions: The effective half-life (Te) of In-111 DTPA from whole-body cisternogram and Ommayogram provides useful dignostic values for evaluation of CSF flow, CSF leakage and extravazation.