Is an 192Ir permanent seed implant feasible for prostate brachytherapy?

(125)I permanent seed brachytherapy for prostate cancer produces good clinical outcomes and limits radiation exposure to medical staff and patients' families. However, (125)I seeds cost thousands of dollars per implant. An encapsulated (192)Ir permanent seed possibly could cost less than 10 dollars. Could inexpensive permanent (192)Ir seeds be used for prostate implants?

We review the radiobiology of permanent implants, calculate the (192)Ir permanent seed air kerma strength (activity) required, simulate (125)I and (192)Ir seed implants and mixtures thereof, calculate exposure rates near simulated (192)Ir prostate patients, calculate potential radiation exposure to medical staff and family members, review patient release regulations, and analyze the potential cost benefits of using (192)Ir permanent seed implants.

Low air kerma strength (<0.4 microGy m(2)/h/seed) [activity < 0.1-mCi/seed; <0.0558 mg Ra eq/seed] permanent (192)Ir seed implants yield more uniform prostate doses than (125)I seed implants and acceptable urethra, bladder, and rectal doses. The (192)Ir 73.83-day half-life allows mixing (192)Ir seeds and (125)I seeds.

We believe medical staff could safely implant 40 microGy m(2)/h [10-mCi; 5.58 mg Ra eq] (192)Ir per case. Occupancy factors (1/8, 1/16) could acceptably limit families' exposures. Seed costs could be reduced markedly. With adequate protection of medical staff and proper instructions to patients post-implant, low air kerma strength (<0.4 microGy m(2)/h/seed) [activity <0.1-mCi/seed; <0.0558 mg Ra eq/seed] (192)Ir permanent seed implants are feasible in large patients, with mixed ((125)I, (92)Ir) seed implants feasible for modest size patients. Such implants could be useful in populous countries (China, India, Brazil) and for others who find (125)I seed implants too expensive to perform.