Dosimetric penumbra effects in catheter-based intravascular brachytherapy using a centered photon or beta line source

Area of Science:

• Medical Physics
• Radiation Oncology
• Cardiovascular Interventions

Background:

• Catheter-based intravascular brachytherapy uses linear sources (photon or beta emitters) to treat blood vessels.
• Dose distribution and gradient are critical factors influenced by radionuclide type and source geometry.
• Understanding dose fall-off at source edges is essential for effective treatment planning and minimizing side effects.

Purpose of the Study:

• To investigate and quantify the dose fall-off at the longitudinal edges of linear brachytherapy sources.
• To compare the edge effects of various photon and beta emitters used in intravascular brachytherapy.
• To analyze the impact of radial depth and source length on dose uniformity and margin length.

Main Methods:

• Calculated dose distributions in cylindrical blood vessels for radionuclides: 192Ir, 125I, 103Pd (photon), and 188Re, 32P, 90Y/Sr (beta).
• Modeled sources as lines and computed dose rates using Monte Carlo simulations for radiation transport.
• Defined and calculated Longitudinal Dose Uniformity (LDU), Effective Coverage Length (ECL), and Margin Length (ML) to characterize edge effects.

Main Results:

• Beta emitters demonstrated superior longitudinal dose uniformity and coverage compared to photon emitters.
• Typical Margin Lengths (ML) were 2-3 mm for beta emitters and 4-6 mm for photon emitters.
• ML increased with radial depth and source length, particularly pronounced for photon emitters.

Conclusions:

• A novel formalism effectively quantifies dose uniformity and edge effects in intravascular brachytherapy.
• Beta emitters provide more favorable dose fall-off characteristics at source edges than photon emitters.
• Margin length is a critical parameter influenced by emitter type, radial depth, and source length, requiring careful consideration in treatment planning.