¹⁵³Sm-EDTMP Appears to Accumulate Only Trivially Within Peritoneal Ascites

CASE REPORT

This patient was referred for treatment with ¹⁵³Sm-EDTMP by her oncologist. During initial consultation with the nuclear medicine physician on a Friday, the patient disclosed that she had an indwelling peritoneal catheter that was used for intermittent drainage of accumulated peritoneal ascites. Around the time of treatment with ¹⁵³Sm-EDTMP, the patient's home health nurse accessed the catheter twice per week (on Tuesdays and Fridays), draining 1–2 L of ascitic fluid each time. Review of imaging studies, laboratory data, and the patient's symptomatology indicated that the patient was an appropriate candidate for ¹⁵³Sm-EDTMP therapy, and the decision was made to proceed with treatment the following week. Drainage of peritoneal fluid was performed on a Tuesday afternoon. ¹⁵³Sm-EDTMP in a treatment dose of 2.62 GBq (70.7 mCi) was administered intravenously the next day (i.e., on Wednesday afternoon). After injection of the treatment dose, the small amount of residual ¹⁵³Sm-EDTMP left in the syringe was washed with saline and 5 mL of this total volume was transferred to a test tube to serve as a standard for subsequent analysis.

On Friday morning (i.e., approximately 44 h after ¹⁵³Sm-EDTMP injection), 1.71 L of peritoneal fluid were drained (using standard, universal precautions) via the patient's indwelling catheter. This fluid was then transported (in a manner compliant with state and federal regulations) to the nuclear medicine laboratory at our medical center for analysis and disposal at approximately 49 h after initial ¹⁵³Sm-EDTMP injection. The ¹⁵³Sm-EDTMP standard was diluted to an activity of 81.4 kBq (2.2 μCi) in a 5-mL volume; this dilution was performed to avoid dead-time loss in the well counter due to a high counting rate, which may invalidate results. After the drained peritoneal fluid was transferred into a large graduated cylinder to measure its total volume, a 5-mL sample was injected into a capped test tube. The sample and the ¹⁵³Sm-EDTMP standard (both in a 5-mL volume) were then assayed in a well counter. After a background count was acquired, activity in each sample was measured (each sample was counted in a well counter for 60 s × 3 iterations). Counts were corrected for background activity and averaged via arithmetic mean.

Study data are summarized in Table 1. Mean background-corrected activity in the 5-mL peritoneal fluid sample was 8,298 cpm, and mean background-corrected activity in the 5-mL/81.4-kBq standard ¹⁵³Sm-EDTMP sample was 1,828,333 cpm. The ratio of activity in the peritoneal fluid to that of the standard was 0.454%, thus representing an activity of 369.26 Bq (9.98 nCi) in the 5-mL sample. This represents a total of 126.17 kBq (3.41 μCi) in the entire 1.71-L volume of peritoneal fluid on Friday, or 263.07 kBq (7.11 μCi) in the entire 1.71-L volume of peritoneal fluid if decay-corrected back to the time of the ¹⁵³Sm-EDTMP injection. Thus, the ratio of total activity in the peritoneal fluid relative to the injected ¹⁵³Sm-EDTMP dose was approximately 0.01%.