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REAL-TIME BRACHYTHERAPY


In the early 1990's Dr Stock, working with his urologic collegue Dr Nelson Stone developed a real-time technique for performing uotrasound guided brachytherapy. Tthis technique relies on real-time transrectal state of the art ultrasound to guide needle and seed placement. Dr Stock,  Dr Stone,  as well has Dr Stock's  students have taught this technique to physicians throughout the United States, Europe and Asia.  It is the technique most commonly used in Europe, Africa  and Japan.  Below is an expert from a review article witten by Dr Stock which describes the technique.

(taken from Stock RG, Stone NN. Current topics in the treatment of prostate cancer with low-dose-rate brachytherapy. Urol Clin North Am. 2010 Feb;37(1):83-96,

THE DEVELOPMENT OF A REAL-TIME ULTRASOUND-GUIDED IMPLANT TECHNIQUE

The advent of transrectal ultrasound-guided brachytherapy was first reported by Holm and Gammelgaard1 in Denmark in 1981. These investigators described the use of transrectal ultrasound to help guide needle and seed placement in the treatment of localized prostate cancer using iodine 125 (125I) radioactive seeds.2 In the last 26 years, there have been many significant advances in low-dose-rate brachytherapy techniques, all derived from this initial approach.

Real-Time Brachytherapy Continued

 

This article outlines the real-time method of ultrasound-guided implantation developed at Mount Sinai Hospital, New York, in 1990.3 The original technique was based on the concept that a preplan of seed placement could never be exactly duplicated in the operating room because of changes in the shape of the prostate and its position relative to the bladder and rectum. Instead, a technique was developed to take into account prostate mobility and use the imaging capabilities of transrectal real-time ultrasound. Using ultrasound, the physician could monitor the position of the prostate during the operation and the seeds could be placed based on the live image of the gland. To further simplify the planning aspect, a lookup table was developed. The amount of radioactivity to implant was derived from the original Memorial Sloan Kettering Cancer Center (MSKCC) nomogram for 125I volume implants.

This nomogram allowed calculation of the amount of radioactivity to implant based on the volume measured to deliver a matched peripheral dose of 160 Gy.4 The basic concept behind the technique is simple and consists of 2 phases. The first phase is called the peripheral phase and involves insertion of needles into the largest transverse diameter of the gland approximately 1 cm apart. Approximately 75% of the radioactivity that is implanted is placed within the prostate via these needles. The seeds are distributed evenly throughout these needles, although needles traversing longer lengths of prostate tend to deposit 1 or 2 more seeds than shorter-length needles. The exact position of the needles and seed deposition is monitored by longitudinal live ultrasound imaging. The second phase involves the placement of interior needles (usually 58 needles) in such a way that the needles cover the apex and base of the gland. The remaining 25% of the activity is implanted through these needles. In the original technique, usually 3 to 4 seeds were deposited per needle. The exact placement of seeds via these needles is also monitored with longitudinal ultrasound imaging. The final version of the Mount Sinai Hospital lookup table for activity per volume to be implanted was developed by using a quality insurance program that was based on monthly examination and review of the computed tomography (CT)-based postimplant dosimetric analyses of all implants. This quality improvement program led to an overall increase in the activity implanted per volume compared with the original MSKCC nomogram. In addition, improvements in ultrasound technology led to better visualization and more accurate placement of sources.5 The final amount of activity implanted per volume used in the Mount Sinai lookup table was found, in a paper by Bice and colleagues,6 to be consistent with other preplanning implant centers. The next development in the technique of realtime ultrasound-guided seed implantation was the implementation of an intraoperative computer planning system. This system allowed for realtime capture of ultrasound prostate images. These prostate images could be captured with needles in place. This feature enabled the physician to recreate the actual implant in 3 dimensions on the computer. The program then allowed for interactive monitoring of delivered dose based on needle and seed deposition positions. In addition, it allowed for fine-tuning of needle positions and overall activity implanted. In a study by Stone and colleagues7 intraoperative ultrasound dosimetry findings were compared with 1-month CT-based postimplant results. Although small differences existed between the intraoperative and CT dosimetry results, these data suggested that this intraoperative implant dosimetric representation system provided a close match to the actual delivered doses (7). It supported the concept that intraoperative dosimetry could be used to modify the implant during surgery to achieve more consistent dosimetry results.

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