Multi-species prostate implant treatment plans incorporating 192Ir and 125I using a Greedy Heuristic based 3D...

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Medicine

Background:

• Interstitial brachytherapy aims for uniform dose delivery while sparing organs at risk.
• Minimizing radioactive sources and implantation needles is crucial for patient safety and treatment efficiency.
• Current prostate brachytherapy often utilizes single-isotope seeds, primarily Iodine-125 (125I).

Purpose of the Study:

• To investigate the efficacy of a multi-species source arrangement using both Iridium-192 (192Ir) and Iodine-125 (125I) seeds for interstitial prostate brachytherapy.
• To evaluate the impact of mixing 192Ir seeds with 125I seeds on dose distribution, organ sparing, and treatment parameters.
• To assess the influence of different 192Ir seed activities on treatment uniformity and efficiency.

Main Methods:

• A Greedy Heuristic optimization algorithm utilizing an "adjoint ratio" was employed to rank source positions.
• Three treatment cases were simulated: Case I (125I alone), Case II (0.12 mCi 192Ir + 125I), and Case III (0.25 mCi 192Ir + 125I).
• Dose exposure to the urethra, central prostate, rectum, and normal tissues was analyzed, alongside the number of seeds and needles required.

Main Results:

• Both multi-species cases (II and III) demonstrated reduced radiation exposure to the urethra and central prostate compared to the base case (I).
• Case III showed a greater increase in rectal and normal tissue exposure than Case II, attributed to the slower dose falloff of 192Ir.
• Multi-species implants significantly decreased the total number of seeds and needles, with Case III requiring fewer than Case II.
• Increasing the number of 0.12 mCi 192Ir seeds in multi-species implants led to improved dose uniformity.
• Acceptable treatment plans with enhanced uniformity were achieved for various prostate sizes using 0.12 mCi 192Ir and 0.4 mCi 125I seeds.

Conclusions:

• The combination of 192Ir and 125I seeds in interstitial prostate brachytherapy offers advantages in dose uniformity and reduction of implant material.
• Careful selection of 192Ir seed activity and number is essential to balance improved uniformity with potential increases in dose to surrounding normal tissues.
• Multi-species brachytherapy presents a viable strategy for optimizing prostate cancer treatment, particularly for achieving better dose conformity and efficiency.