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

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

Purpose: ¹²⁵I permanent seed brachytherapy for prostate cancer produces good clinical outcomes and limits radiation exposure to medical staff and patients' families. However, ¹²⁵I seeds cost thousands of dollars per implant. An encapsulated ¹⁹²Ir permanent seed possibly could cost less than $10. Could inexpensive permanent ¹⁹²Ir seeds be used for prostate implants? Methods and Materials: We review the radiobiology of permanent implants, calculate the ¹⁹²Ir permanent seed air kerma strength (activity) required, simulate ¹²⁵I and ¹⁹²Ir seed implants and mixtures thereof, calculate exposure rates near simulated ¹⁹²Ir prostate patients, calculate potential radiation exposure to medical staff and family members, review patient release regulations, and analyze the potential cost benefits of using ¹⁹²Ir permanent seed implants. Results: Low air kerma strength (<0.4 μGy m²/h/seed) activity < 0.1-mCi/seed; <0.0558 mg Ra eq/seed] permanent ¹⁹²Ir seed implants yield more uniform prostate doses than ¹²⁵I seed implants and acceptable urethra, bladder, and rectal doses. The ¹⁹²Ir 73.83-day half-life allows mixing ¹⁹²Ir seeds and ¹²⁵I seeds. Conclusions: We believe medical staff could safely implant 40 μGy m²/h 10-mCi; 5.58 mg Ra eq] ¹⁹²Ir 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 μGy m²/h/seed) activity <0.1-mCi/seed; <0.0558 mg Ra eq/seed] ¹⁹²Ir permanent seed implants are feasible in large patients, with mixed (¹²⁵I, ⁹²Ir) seed implants feasible for modest size patients. Such implants could be useful in populous countries (China, India, Brazil) and for others who find ¹²⁵I seed implants too expensive to perform.