tissue toxicity. Evidence continues to accumulate demonstrating the importance of dose escalation in prostate cancer. In order to deliver an acceptable dose via EBRT, patients may undergo several weeks of treatment, whereas brachytherapy can be completed during an outpatient procedure or a short hospitalization. Finally, the position of the prostate and surrounding critical organs may be difficult to reproduce daily during a protracted course of treatment, which may lead to an increased dose to normal tissues or a decreased dose to the prostate. Potential disadvantages to brachytherapy compared to external beam radiotherapy are that it may take longer to develop brachytherapy skills, is at least minimally invasive with a higher risk of urinary retention, and requires anesthesia. Compared to surgery, the risk of bowel changes and toxicity may be greater with brachytherapy.
TABLE 34.1 PATIENT SELECTION FACTORS
risk of severe lower urinary tract symptoms (LUTS) and acute urinary obstruction following brachytherapy (16). Similarly, large prostates have been shown to be at increased risk for urinary retention (17), although the absolute risk may still be low depending on the technique used (18). Patients with a history of prior TURP may be at increased risk for significant toxicity, including incontinence, if LDR brachytherapy is used (19,20), especially if the residual TURP deficit is large. This risk may be less with HDR brachytherapy (20a).
TABLE 34.2 CHARACTERISTICS OF THE MOST COMMONLY USED PERMANENT SOURCES
TABLE 34.3 TYPICALLY PRESCRIBED MINIMUM PERIPHERAL DOSES FOR 125I AND 103PD
volume determined at TRUS done for the initial biopsy. The patient is then brought to the OR and placed in the dorsal lithotomy position. TRUS is used to localize the bladder, urethra, prostate, seminal vesicles, and anterior rectal wall in three-dimensional space, and these data are recorded in the intraoperative treatment planning software (Fig. 34.4). An initial intraoperative plan is then developed based on a prostate volume-to-activity nomogram developed at MSSM. Needles are placed in the periphery of the prostate at approximately 1-cm intervals (Fig. 34.5). Once the needles are placed, images are reacquired to account for changes in size, shape, and position of the prostate that occurs with the inflammation induced
by multiple needle placement (Fig. 34.6). The plan is optimized for actual position of the needles and for any changes in shape of the prostate due to needle placement. Longitudinal views on the TRUS are used to observe placement of the seeds into the prostate according to the intraoperative plan (Fig. 34.7). Seeds are most often placed using a Mick applicator. Typically 75% of the required activity is placed in the periphery of the gland, while 25% is placed in the interior of the gland. Then needles are placed in the central portion of the gland and the Mick applicator is then used to place the remaining 25% of the required activity in the gland according to the intraoperative plan. The majority of the inner seeds are placed at the apex and base of the gland in order to “cap” the prostate. Using modern treatment planning software and TRUS, the actual seed location can be documented as the seeds are placed and the intraoperative plan can better reflect reality, allowing for dosimetric inadequacies to be detected and corrected during the procedure.
FIGURE 34.4 Ultrasound imaging of the prostate, urethra, seminal vesicles, and rectum in the intraoperative treatment planning system before needle placement. This data set is used to create the “preplan” in the OR.
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