Prostate Brachytherapy: Comparison of Dose Distribution with Different 125I Source Designs

David C. Beyer, MD ; Fred Puente, CMD ; Kevin L. Rogers, MS ; Erdal M. Gurgoze, PhD

1 From Arizona Oncology Services, 8994 E Desert Cove Ave, Suite 100, Scottsdale, AZ 85260. From the 2000 RSNA scientific assembly. Received December 13, 2000; revision requested February 3, 2001; revision received April 9; accepted May 1.

PURPOSE: To evaluate the interchangeability of various commercially available iodine 125 (125I) sources and to assess the dosimetric effect of a change in source.

MATERIALS AND METHODS: A modified peripherally loading prostate brachytherapy plan to deliver 145 Gy was devised by using a model 125I source, which until recently was the only available 125I source. A dose-volume histogram was generated. By using the available radial dose functions and anisotropy distributions for eight other currently commercially available sources, the same implant placement was planned and dose-volume histogram distributions tabulated. This exercise was performed for 15-, 45-, and 60-cm3 glands. No implants were placed, and no physical radiation measurements were made. Dose calculations were theoretic: They were generated by using a widely available treatment planning system.

RESULTS: There was little difference in dose distribution to the volume receiving 100% of the prescribed dose (<6%); only one source showed a difference greater than 2%. Large differences, up to −40% to +60%, were seen in the volume of tissue encompassed within internal high-dose regions receiving 150% or 200% of the prescribed dose. These findings held true, irrespective of gland size, within a clinically relevant range (15–60 cm3) and for a uniformly loaded radionuclide distribution.

CONCLUSION: Reviewing only peripheral dose at or near the prescription dose of 145 Gy revealed little difference in doses for various source designs. Marked differences in high-dose regions were seen and may affect the dose received by internal sites. Effects of these changes on cure and/or complications remain speculative.