brachtherapy details

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More details on Brachytherapy

External beam radiation therapy produces survival rates that are at least equal to those observed with radical prostatectomy, with complication rates are generally reduced compared to radical prostatectomy. The incidence of complications is further reduced by conformal radiotherapy, indicating the advantage of conformal treatment volumes. Brachytherapy provides intrinsically conformal radiotherapy for two reasons: first, there is no irradiation of normal tissue between the patient's surface and the treatment volume; and second, by optimizing the seed placement, the treatment volume can be made to closely approximate the target volume. The short treatment times involved for both temporary and permanent implants make this treatment especially attractive for active patients.

Brachytherapy is a form of radiation therapy in which physicians implant radioactive pellets or seeds into the prostate gland in order to kill prostate cancer cells. The term "brachytherapy" was coined by Forsell in 1931. It is derived from the Greek word brachio, meaning short, and refers to "treatment with a radioisotope at a short distance". This method is also called "Radioactive Seed Implantation" or "Internal Radiation Therapy"

Most radiation treatments are delivered with teletherapy, in which the source of radiation is distant form the target; in brachytherapy, the source is placed in or near the target. Because the radioactive sources used in Brachytherapy deposit all of their absorbed dose within a few millimeters of the source, the sources can be arranged so the radiation dose delivered to adjacent normal tissues is minimized, and the dose delivered to the target volume itself is maximized.

Early brachytherapy treatments involving manual placement of the seeds, which exposed the practitioner to high radiation doses, have been superseded by afterloading techniques, in which a hollow needle or applicator is placed in the target. The radioactive source is then positioned through this channel. The occupational exposures encountered in this manual afterloading have been further reduced with the introduction of remote afterloading, which uses a mechanical device to load the source by remote control. Remote afterloading, which uses sources of high activity, has allowed the introduction of high dose rate and pulsed dose rate brachytherapy, which would otherwise give prohibitively large radiation doses to hospital personnel.

Although the use of radium to treat prostate cancer was reported in 1913, interest in brachytherapy remained low due to the radiation exposure to operating room staff. The introduction, in the early 1960s, of megavoltage linear accelerators capable of producing improved teletherapy dose distributions slowed the development of brachytherapy. Shortly thereafter, however, the development of afterloading techniques renewed interest in brachytherapy. By the mid-1980s, a number of radioactive implantation procedures for prostate carcinoma had been described in the literature.

Retropubic implantation of the prostate, which produced poor dose uniformity, has been replaced by transperineal implantation because the development of transrectal ultrasound (US) Transperineal implants can be used alone or in combination with EBRT in the treatment of prostate cancer. Complication rates with brachytherapy are minimal, and are more likely to occur in patients who have undergone transurethral resection of the prostate (TURP). Otherwise, patients who undergo transperineal implantation show excellent quality of life.

Permanent Implants

Diagram of transperineal permanent brachytherapy

In a permanent implant, the radioactive sources are permanently implanted into the tumor and allowed to decay. Hence, neither the dose nor the dose distribution can be changed after the initial insertion. It is, however, a simple procedure, and some of them can be done on an out-patient basis. Other advantages of the permanent implant are that, in deep-seated tumors, it is safer because of the lower risk of infection and that a second operation for its removal is not required. Permanent implantations are performed with relatively short half-life radiosotopes like iodine-125, palladium-103, or gold-198.

Removable (Temporary) Implants

In a removable implant, the radioactive material is temporarily implanted into or close to the tumor and is removed once the desired radiation dose has been delivered. Therefore, there is better control of the total dose and the dose distribution. Removable implants are more time consuming. Their principle indication is the treatment of accessible tumors where the aim is cure, or at least long-term palliation.

HDR remote afterloader