Dose calculation for permanent prostate implants incorporating spatially anisotropic linearly time-resolving edema

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry

Background:

• Permanent prostate implants are used for brachytherapy.
• Prostatic edema (swelling) can affect radiation dose distribution.
• Accurate dosimetry is crucial for effective treatment and minimizing side effects.

Purpose of the Study:

• To develop a dose calculation method for permanent prostate implants that accounts for clinically relevant edema.
• To quantify the preimplant dosimetry error caused by edema using this new method.

Main Methods:

• Developed a model for spatially anisotropic, time-resolving prostatic edema based on MRI data.
• Extended the TG-43 dose calculation formalism to incorporate the edema model.
• Calculated preimplant dosimetry error for 125I, 103Pd, and 131Cs seeds under various edema conditions.

Main Results:

• The developed method indicated underdosage in the calculation volume, dependent on seed and calculation point positions.
• Dosimetry errors increased with greater edema magnitude and duration.
• For average edema, mean errors were 8.3% for 131Cs, 7.5% for 103Pd, and 2.2% for 125I seeds.

Conclusions:

• A novel dose calculation method for permanent prostate implants incorporating anisotropic, time-resolving edema was established.
• This method provides different dosimetry error values compared to isotropic edema models.
• The method is applicable for calculating dosimetry corrections when edema can be estimated or measured.