Treatment techniques

3.3.1. Preplanned transperineal implantation techniques

First of all, TRUS imaging is obtained before planned procedure to assess the prostate volume. A computerized plan is generated from the ultrasound images, producing isodose distributions and the ideal location of seeds within the gland to deliver the prescription dose to the prostate. Several days to weeks later, the implantation procedure is performed. Needles are then placed under ultrasonographic guidance through a perineal template according to the coordinates determined by the preplan. Radioactive seeds are individually deposited in the needle with the aid of an applicator or with preloaded seeds on a semirigid strand containing the preplanned number of seeds. In the latter case, this is accomplished by stabilizing the needle obturator that holds the seed column in a fixed position while the needle is withdrawn slowly, depositing a row or series of seeds within the gland.

In general most brachytherapists use a modified peripheral loading technique for permanent interstitial implantation. This approach can reduce the urethral doses more than a homogenous loading technique. The portion of the urethra receiving 150% dose (UV150) should be limited [52]. Likewise, the volume of the rectum (RV100) receiving the prescription dose ideally should be < 1 cc [53].

3.3.2. Intraoperative planning techniques

Intraoperative planning takes advantage of the opportunity of using real-time measurements of the prostate during the procedure while preplanning is often preformed several weeks before implantation, frequently under different conditions than the actual operative procedure. Subtle changes in the position of the ultrasound probe as well as the distortion of the prostate associated with needle placement and subsequent edema can result in profound changes in the shape of the gland compared with the preplanned prostatic contour.

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