Abstract
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 m
2/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 m
2/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 m
2/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.