High-dose-rate Brachytherapy of Prostate Cancer

US Oncological Disease, 2007;1(2):98-102 DOI: http://doi.org/10.17925/OHR.2007.00.2.98
Citation US Oncological Disease, 2007;1(2):98-102 DOI: http://doi.org/10.17925/OHR.2007.00.2.98

Measurement of blood levels of prostate-specific antigen (PSA) and greater awareness have led to the detection of prostate cancer at an earlier and potentially more curable stage. As certain kinds of prostate cancer progress very slowly, some patients choose to undergo clinical observation (‘watchful waiting’) rather than active treatment. Alternatively, surgery and radiation therapy (RT) are the only curative treatment options. Hormone therapy (androgen deprivation) is another intervention used to enhance curative treatment or treat recurrent disease. RT can be administered in various ways, including external beam (EB), brachytherapy (the placement of a radiation source directly into a tumor), or a combination of both methods. Brachytherapy effectively targets the prostate and minimizes the dose to adjacent organs such as the bladder and rectum, because the dose decreases very rapidly as the distance from the radiation source increases.

There are two types of prostate brachytherapy: high-dose-rate (HDR) and permanent-seed. HDR brachytherapy is a precision technology for the placement of a brachytherapy source that employs robotic technology to temporarily deliver a high-intensity radiation source into the prostate and surrounding tissue. HDR is applicable to virtually all stages of localized prostate and many other types of cancer. It may be given as the only treatment (HDR monotherapy) for early disease or used in combination with external RT for locally advanced or higher-stage cancer. This article will describe HDR brachytherapy for prostate cancer.

High-dose-rate Brachytherapy
HDR describes more than the rate at which the radiation dose is given; it also offers a new dimension to brachytherapy. A single high-intensity radiation source located at the end of a wire is robotically inserted into thin brachytherapy catheters (close-ended straws) that have been temporarily inserted into the prostate. Instead of having a large number of uniformstrength permanent seeds, HDR applies a single radiation source that is time- and position-controlled during the treatment process. The longer the source stays in a particular location, the greater the effective radiation dose. Thus, HDR offers an infinite variety of source strengths at each of the hundreds of locations within the implant.

Along with the millimeter precision of source insertion, HDR provides the best opportunity to shape and control the distribution of the radiation. Delivery of treatment takes only about 20 minutes and occurs in a series of applications given over several hours or days. The radiobiology of prostate cancer favors large doses of radiation per session, thus HDR is well-suited for the control of prostate cancer. Due to the short duration of therapy, HDR has the benefit of a correspondingly short period of acute side effects.

The temporary HDR brachytherapy catheters act as stable scaffolding to permit precise and reproducible placement of the radiation source within and around the prostate gland. Consequently, there is a high degree of dose uniformity within the gland and excellent coverage of disease just beyond the edge of the prostate. Importantly, unlike with permanentseed brachytherapy, the dose of radiation is known before treatment and can be adjusted and individually tailored. There is no radiation exposure to medical personnel or families and seed migration to other organs cannot occur. Organ motion, of great concern in EBRT, is not a problem with HDR as the applicator is fixed to the target. Rectal doses are predictably low with HDR brachytherapy compared with EBRT.

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