Long-term complications with prostate implants: Iodine-125 vs. palladium-103

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Abstract
The linear quadratic model predicts that the normal tissue biologically effective dose (BED) will be lower with palladium‐103 (Pd‐103) vs. iodine‐125 (I‐125) for the currently prescribed minimum tumor doses (MTD) used for I‐125 (160 Gy) and Pd‐103 (115 Gy) prostate cancer brachytherapy. The predicted BEDs for I‐125 and Pd‐103 suggest that the long‐term complication rates should be lower with Pd‐103 vs. I‐125 in clinical practice. A review of 123 early stage T1c and T2 prostate cancer patients implanted at Yale University with I‐125 (82 patients) or Pd‐103 (41 patients) reveals a significantly lower overall complication rate with Pd‐103 (0%) vs. I‐125 (13%). Most important, the grade III–IV complication rate for Pd‐103 was 0% vs. 6% for I‐125. The 3‐year actuarial probability of remaining free of a long‐term complication was 100% for Pd‐103 vs. 82% for I‐125 (P < 0.01). A review of the literature for 992 patients implanted with I‐125 vs. 540 patients implanted with Pd‐103 shows a consistently higher complication rate for I‐125 vs. Pd‐103. Assuming that the MTD for Pd‐103 may be increased to produce an equivalent late‐reacting normal tissue BED to that for I‐125, then the radiobiology model predicts the log10 cell kill for Pd‐103 implant will be greater than that of an I‐125 implant for all tumor doubling times (high‐grade tumors and low‐grade tumors). The implications of these findings are discussed in terms of future research directions for prostate implants. Radiat. Oncol. Invest. 7:278–288, 1999.

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