Modification of prostate implants based on postimplant treatment margin assessment

Area of Science:

• Medical Physics
• Radiation Oncology
• Urology

Background:

• Prostate brachytherapy is a common treatment for localized prostate cancer.
• Achieving optimal dose distribution and coverage is crucial for treatment efficacy.
• Uniform treatment margins (TMs) are essential for ensuring adequate dose delivery to the entire prostate gland.

Purpose of the Study:

• To quantify the additional radioactive source placement required to achieve uniform 5 mm treatment margins (TMs) after standard prostate brachytherapy implantation.
• To evaluate the impact of achieving uniform TMs on dosimetric parameters.

Main Methods:

• Ten patients undergoing Iodine-125 (I-125) brachytherapy for prostate cancer were studied.
• Postimplant dosimetry was performed using CT scans within 2 hours of implantation.
• Treatment margins were measured, and additional sources were manually added to achieve a minimum 5 mm TM around the prostate periphery.

Main Results:

• Standard implantation techniques did not uniformly achieve 5 mm TMs.
• An average of 17% additional sources were required to achieve minimum 5 mm TMs.
• Achieving uniform TMs increased the median V100 from 96% to 100% and the median D90 from 116% to 160% of prescription dose.
• Additional sources increased the prostate volume receiving >200% of prescription dose (V200) and the average urethral point dose.

Conclusions:

• Current standard brachytherapy techniques are insufficient for uniformly achieving 5 mm treatment margins.
• Reappraisal of implant techniques or integration of intraoperative dosimetry with the ability to add sources is necessary.
• Optimizing TMs may require adjustments to current implantation protocols.