Personalized radiation dosimetry for PRRT-how many scans are really required?

Area of Science:

• Nuclear Medicine
• Radiotherapy Physics
• Oncology

Background:

• Peptide receptor radiotherapy (PRRT) is a key treatment for metastatic neuroendocrine tumors (NETs).
• Personalized dosimetry is crucial for optimizing PRRT outcomes by balancing tumor dose and normal organ toxicity.
• Accurate absorbed dose calculation relies on time-activity concentration curves (TACCs) derived from SPECT/CT imaging.

Purpose of the Study:

• To investigate the impact of TACC data points and numerical integration methods on absorbed dose calculations in ¹⁷⁷Lu-DOTATATE PRRT.
• To determine the minimum number of post-treatment SPECT/CT scans required for reliable dosimetry in NET patients.

Main Methods:

• Retrospective analysis of SPECT/CT scans from 30 patients undergoing ¹⁷⁷Lu-DOTATATE PRRT.
• Calculation of absorbed dose and effective half-life using varying numbers of time points (2, 3, or 4) in the TACC.
• Comparison of different numerical integration methods (mono-exponential fit, trapezoidal rule) against a standard combined method.

Main Results:

• Absorbed dose estimates using only 3 scans (24h, 4-5 days, 1 week) showed minimal differences (<2.5%) compared to the standard 4-scan method.
• Using only 2 scans (24h and 1 week) also yielded relatively small differences (<3.5%).
• The early 4-hour scan point in a 4-point mono-exponential fit could introduce significant errors.

Conclusions:

• Accurate dosimetry for ¹⁷⁷Lu-DOTATATE PRRT may be achievable with scans at 24 hours, 72 hours, and 1 week post-treatment.
• Reducing the number of scans, potentially omitting the 72-hour scan, could streamline dosimetry, though with increased uncertainty.
• Further validation in larger patient cohorts is necessary to confirm these findings.