166Ho-DOTMP radiation-absorbed dose estimation for skeletal targeted radiotherapy

Area of Science:

• Nuclear Medicine
• Radiopharmaceutical Therapy
• Pharmacokinetics

Background:

• 166Ho-DOTMP is a bone-seeking radiopharmaceutical used for treating multiple myeloma.
• Accurate dosimetry is crucial for optimizing therapeutic efficacy and minimizing toxicity.

Purpose of the Study:

• To evaluate the pharmacokinetics and radiation-absorbed dose of 166Ho-DOTMP in patients with multiple myeloma.
• To compare different methods for estimating organ doses, particularly for the kidneys.

Main Methods:

• Whole-body retention was assessed using gamma-camera or uptake probe in 12 patients after 166Ho-DOTMP administration.
• Radiation-absorbed doses were estimated using MIRD methodology, including residence times and S values.
• Kidney dose was estimated using region-of-interest (ROI) and whole-body clearance methods; bladder dose was estimated using a dynamic bladder model.

Main Results:

• Gamma-camera methods proved more reliable than uptake probes for whole-body counting.
• Skeletal uptake ranged from 19% to 39% (mean 28%).
• Kidney dose estimates varied significantly between methods (1.6-4 Gy vs. 8.3-17.3 Gy), with neither deemed fully reliable. Bladder and bone surface doses were 10-20 Gy and 39-57 Gy, respectively.

Conclusions:

• Gamma-camera whole-body counting is suitable for assessing 166Ho-DOTMP clearance and estimating organ doses, excluding the kidneys.
• Quantitative gamma-camera imaging requires scatter subtraction due to 166Ho's emissions.
• Further evaluation is needed to refine kidney dose estimation methods for 166Ho-DOTMP therapy.