Regional treatment margins for prostate brachytherapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Urologic Oncology

Background:

• Accurate dosimetry is crucial for effective prostate cancer treatment with (125)I seed implants.
• Understanding postimplant dose distribution variations is essential for optimizing treatment outcomes.

Purpose of the Study:

• To quantify the treatment margin (TM) around the prostate receiving 100% of the prescribed dose.
• To analyze regional postimplant dosimetry within the prostate for (125)I seed implants.

Main Methods:

• Created an average target volume (ATV) from postoperative MRI contours of 40 patients.
• Fused MRI with postoperative CT for dosimetry, measuring TM at 16 points across prostate regions (base, midgland, apex).
• Assessed dose to 90% of ATV (D90) and % of ATV receiving prescribed dose (V100) for the whole prostate and its four quadrants.

Main Results:

• Mean TM varied significantly: -8.88 to 3.68 mm (base), 1.12 to 10.42 mm (midgland), and 6.27 to 18.25 mm (apex).
• Mean D90 values for quadrants were: anterior-superior (135.8 Gy), posterior-superior (162.8 Gy), anterior-inferior (191.0 Gy), and posterior-inferior (194.6 Gy).
• The anterior base was identified as the most underdosed region.

Conclusions:

• Postoperative treatment margins around the prostate are variable despite uniform preoperative planning.
• The anterior prostate base is significantly underdosed, while lateral regions of the midgland and apex receive ample dose.
• Dosimetric parameters were lowest in the anterior-inferior quadrant, indicating potential areas for improved dose coverage.