The effects of permanent I-125 interstitial implantation on cortical bone

From 1973 to 1980, 1,427 cancer patients were treated by the Brachytherapy Service, Radiation Oncology Department of Memorial Sloan-Kettering Cancer Center (MSKCC) with I-125 permanent interstitial implantation. Concern has been expressed with regard to the possible toxic effects of the low average photon energy (28 kev) of I-125 on bone, secondary to its increased absorption in these tissues because of the photoelectric effect. In an attempt to address this concern with respect to cortical bone, we reviewed pertinent data on those patients whose site of implant was at close proximity to osseous tissue in the pelvic, chest wall and head and neck regions. The review included 74 sites in 58 patients having no prior history or clinical evidence of any pathologic or metabolic bony disorder. Long term (greater than 1 year) follow-up was available in over 50% of the cases, with 10 patients followed more than 4 years. Local control rate for the 74 implanted sites was 93%. The implanted activity ranged from 1.6 to 48.8 mCi and the implanted volume from 0.5 to 152 cm3. At this follow-up range, there appears to be no excessive osseous toxicity either clinically or radiologically with I-125 permanent implantation.