A quality-control method for SPECT-based dosimetry in targeted radionuclide therapy.

Area of Science:

• Medical Physics
• Nuclear Medicine
• Radiotherapy

Background:

• Accurate dosimetry is crucial for targeted radionuclide therapy, but standard methods and uncertainty evaluations are lacking.
• Current imaging techniques like SPECT have limitations in spatial resolution for precise absorbed-dose distribution determination.

Purpose of the Study:

• To present an experimental dosimetry method using polymer gel dosimeters and MRI for direct measurement of absorbed-dose distributions.
• To compare absorbed-dose mapping from MRI with traditional SPECT imaging in a phantom study.

Main Methods:

• A phantom with a nonuniform I-131 distribution was prepared in polymer gel.
• Absorbed-dose distributions were determined using T(2) MRI and sequential SPECT imaging.
• MRI data were quantified using calibration vials, and SPECT data utilized the MIRD schema.

Main Results:

• MRI provided direct absorbed-dose distribution mapping, showing good agreement with SPECT (correlation coefficient 0.96) after PSF convolution.
• SPECT imaging misrepresented the absorbed-dose distribution due to its lower spatial resolution, causing shifts in maximum dose localization.
• The MRI-based method demonstrated superior spatial resolution compared to SPECT.

Conclusions:

• Polymer gel dosimetry with MRI offers a direct and accurate method for absorbed-dose distribution determination in targeted radionuclide therapy.
• This technique can serve as an independent benchmark for patient-specific dosimetry and quality control, addressing current dosimetry uncertainties.