Patient-specific dosimetry in radionuclide therapy.

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiotherapy

Background:

• Internal dosimetry is crucial for effective palliative treatment of bone and liver lesions.
• Current methods using planar imaging data have limitations, including lack of attenuation and scatter corrections, and organ overlay.
• Accurate absorbed dose calculation is essential for optimizing patient treatment and minimizing toxicity.

Purpose of the Study:

• To compare individualized palliative treatment absorbed doses calculated by planar imaging data versus Monte Carlo simulation.
• To evaluate the accuracy of absorbed dose estimations in bone metastases and liver lesions.
• To propose advanced methods for patient-specific dosimetry.

Main Methods:

• Utilized Medical Internal Radiation Dose (MIRD) schema for absorbed dose estimation.
• Employed Monte Carlo (MC) simulation to calculate radiopharmaceutical volume distributions and absorbed doses in lesions and critical organs.
• Compared results from planar data calculations with MC simulations in two in vivo cases.

Main Results:

• Planar data calculations showed an overall error of approximately 7% compared to Monte Carlo simulations.
• Monte Carlo simulation provided more accurate absorbed dose calculations, accounting for complex geometries and inhomogeneities.
• Patient-specific 3D dosimetric calculations using SPECT/CT were proposed for enhanced accuracy.

Conclusions:

• Individualized planar data calculations, while common, are less accurate than Monte Carlo simulations due to inherent limitations.
• Monte Carlo simulation, particularly with patient-specific 3D imaging (SPECT/CT), offers a more precise approach to internal dosimetry.
• The use of dose-volume histograms is recommended for evaluating dose distributions in heterogeneous cases.