Seed Implant Produces Optimal Dosing
Traditionally, patients at the Dattoli Cancer Center are treated with several weeks of DART prior to interstitial brachytherapy using Palladium-103 (Pd-103). This dose level typically covers not only the prostate, but also potentially surrounding target tissues (including, but not limited to, seminal vesicles, periprostatic lymph nodes, obturator lymph nodes, internal iliac lymph nodes, and even common iliac and para-aortic nodes per individual case as indicated).
The initial radiation dose was chosen because early physics and radiobiologic evaluations performed by physicists at Memorial Sloan Kettering (MSKCC), especially Dr. Lowell Anderson, suggested that this dose given along with an attenuated dose of palladium-103 of 8000-9000cGy would not exceed rectal, urethral or bladder tolerances. Bear in mind that in the latter 1980’s, no one knew the correct doses when combining EBRT with Pd-103. At that time, the Pd-103 isotope was relatively new and Dr. Anderson was instrumental in characterizing the physical parameters and laid the groundwork for clinical models.
Dr. Dattoli worked closely with Dr. Anderson and other physicists at MSKCC and adopted these dose parameters. The dose, however, is insufficient in most cases to eradicate microscopic, and especially potentially macroscopic cancer cells, at a distance from the prostate gland. For this reason, following the implant procedure, our physics/dosimetry staff then generates precise isodose curves emanating from the seed implant (both inside and outside the gland).
The dose projected by the seeds to a given distance from the prostate can then be precisely calculated up to the point of near complete decay of the palladium 103 at the three month mark post seeding. For this reason, most patients return approximately three months after seeding (at the point of near decay of the isotope) to receive additional “touch up” DART treatments to peripheral target tissue sites while blocking the prostate, bladder, rectum, and proximal penile tissues.
The individualization of the dose is multifactorial including but not limited to taking into account the size of the gland, stage, size of tumor(-s), location of tumor(-s), volume of tumors, immunohistochemical parameters, Gleason score, PSA, PAP, prior TURP/TUIP, etc. The optimal dose to target points at distance from the gland, and the subsequent physics analysis will determine the number of treatments necessary to achieve the desired dose. It is to be noted that this methodology has been in place since the early 1990’s, although, and is now more liberally utilized with DART in view of the safety associated with dose escalation using this latest modality.