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Optimal placement of radioisotopes for permanent prostate implants.

PURPOSE
To determine which of four loading techniques most efficiently yields the prescribed dose to the prostate volume while limiting dose to the central urethral volume.


MATERIALS AND METHODS
The four techniques included (a) equal activity and equal spacing with nomogram, (b) differential loading, (c) peripheral loading, and (d) spiked loading of the lobes. They were evaluated with regard to target coverage urethra dose, tolerance to error, and complexity of procedure.


RESULTS
All ideal plans delivered the prescribed dose of 160 Gy to 99% of the prostate volume. With prostate-volume expansion and source-placement errors, all strategies indicated that at least 71% of the target volume received the prescribed dose and greater than 92% of the target volume received 120 Gy.


CONCLUSION
With source-placement errors and glandular swelling, peripheral loading yields the best target coverage while limiting dose to the central urethral volume.