Multisector prostate dosimetric quality: analysis of a large community database.

Purpose: To evaluate multi-institutional prostate brachytherapy dosimetric quality using multisector analysis.

Methods And Materials: In the database, 4547 patients underwent brachytherapy (3094 for (125)I, 1437 for (103)Pd, and 16 for (131)Cs). The original prostate postimplant dosimetry was reported using the maximum dose covering 90% of the prostate volume (D90) and the percentage of the prostate volume covered by the prescription dose (V100). Retrospectively, the dosimetry of all implants was recalculated after segmenting the prostate into 12 sectors (anterior, left and right lateral and posterior, about the center of gravity, and subdivided lengthwise into three-base, midgland, and apex). The dosimetric quality of each sector and combinations of sectors was compared across radionuclides.

Results: For each radionuclide, there was no significant difference between monotherapy and boost in terms of V100 or D90. When classified as excellent (V100 ≥ 90%), standard (V100 ≥ 80%), or minimal (V100 < 80%), 33.0%, 4.6%, and 10.5% of all base, midgland, and apical sectors, respectively, were of minimal quality. Specifically, 59.2% of the anterior base and 30.3% of the posterior base sectors were minimal. At the anterior midgland and apex, 22% and 19% of sectors were minimal. Excellent quality was observed in more than 90% of lateral and posterior midgland sectors and in >70% of lateral and posterior sectors. When stratified by (103)Pd vs. (125)I, sector analysis did not result in clinically significant dosimetric differences.

Conclusions: Coverage of base sectors was inferior to midgland and apical sectors, and coverage of anterior sectors was notably inferior to lateral and posterior sectors. Further critique of brachytherapy planning and intraoperative technique is necessary for brachytherapists to minimize these dosimetric differences.