Advantages of using high activity 125I seeds in temporary interstitial breast implants

There has been considerable interest in the use of high activity 125I sources as a substitute for 192Ir seeds for removable implants of the breast and prostate. 125I seeds with an initial activity of approximately 5 mCi per seed, loaded in special afterloading nylon catheters, are used to improve dose distribution in the tumor volume and minimize dose to the adjacent critical organs and normal tissues. Seed spacing in strands is adjusted to maintain a dose rate of 40-60 cGy per hour at a distance of 5 mm from the plane of the implant. Implants custom loaded with 125I sources achieve superior isodose distribution compared to implants loaded with standard 192Ir seed strands. High activity 125I seeds also offer the advantage of reduced exposure to radiation oncology staff, nurses, and visitors leading to better patient care. Due to reduced exposure to personnel, the accuracy of the actual implant geometry can be verified by taking a localization film with actual 125I sources placed in the tumor bed.