When prostate cancer spreads, it grows microscopic extensions – a good analogy is the palm of your hand representing the tumor, and your fingers representing the “spiders” or extra-capsular extensions of the cancer. Within just a few weeks of receiving radiation treatment, those extensions begin to retreat back into the tumor.
We have learned that by targeting the tumor and its extensions first with DART, with or without hormones, the seeding procedure is more effective and serves as a boost, while not leaving the migrating cells in the regions outside of the prostate untreated. The surrounding field is sterilized by the daily radiation and cancers are rendered non-viable when external beam is used upfront.
Additionally, when seeds are placed in the prostate, they may cause scattering of the external radiation when it collides and is displaced by the seeds, with the possibility of irradiating healthy surrounding tissue. The available published literature using seeds before radiation has reported higher rates of rectal injury. Finally, we are concerned that placing seeds first in intermediate to high-grade cancers may even spread cancer into the blood stream, resulting in clinical failure at other sites within the body. This has been documented in contemporary brachytherapy literature.
For additional information on this topic, you may consult these two publications:
Zeitlin SL, Sherman J, Raboy A, Lederman G, Albert P. High dose combination radiotherapy for the treatment of localized prostate cancer. J Urol 1998; 160:91-96.
Patel J, Worthen R, Abadir R, Weaver DJ, Weinstein S, Ross G. Late results of combined Iodine-125 and external beam radiotherapy in carcinoma of prostate. Urol 1990; 36:27-30.