Prostate Brachytherapy

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This image has an empty alt attribute; its file name is IMG_0010-1-e1550751225717.jpg — Dr Lyn Oliver AM PhD

Dr Lyn Oliver AM PhD
Retired Medical Physicist

Definition of Brachytherapy

(http://medical-dictionary.thefreedictionary.com/brachytherapy)

Brachytherapy is radiation therapy using a radioactive source placed either within the body or a cavity, on the bodysurface, or a short distance from the surface.

Prostate brachytherapy is a specialised technique used for special prostate cancer patients referred for radiation therapy. Your medical specialist will advise you on this option.

The technique uses ‘sealed” radioactive sources. The term ‘sealed” means that the radioactive substance is either biologically inert or is encased in a metal container which is biologically inert. The sealed radioactive source can be interstitially implanted, inserted into a body cavity or placed onto the surface of the skin for cancer treatment. Once the sealed radioactive source is removed, no residual radioactivity remains in the patient.

Figure 1. Needles are inserted into the prostate with guidance by the ultrasound probe placed in the rectum. The technique is virtually the same for inserting a radioactive source of either iridium-192 or iodine-125.

Many brachytherapy techniques are no longer used. But the use of brachytherapy techniques for gynaecological cancer for women and prostate cancer for men, is still a very valuable method of treatment.

This article describes the use of radioactive iodine-125 and iridium-192 as brachytherapy techniques for prostate cancer.

Low Dose Rate (LDR) Brachytherapy

Radioactive iodine-125 seeds

Radioactive iodine-125 seeds (Figure 2.) can be permanently implanted to irradiate the prostate cancer. This technique is restricted to a protocol for early prostate cancer stage with a specific pathology grade limit.

Figure 2. Radioactive I-125 seeds used for prostate cancer implant.

The seeds remain permanently implanted in the prostate and the radioactivity emitted from these small radioactive seeds slowly decays to a negligible amount. As the dose rate gradually decreases over a long time (years), the radiation stops cell division and kills the prostate cancer cells.

The implanted seeds emit very low energy radiation which irradiates the tumour locally but is not a hazard to the patient or public after the seeds are implanted. The seeds remain permanently in the patient. The medical physicist has expertise in radiation protection and will provide written instructions on this that describe the safety aspects for the patient, relatives and public, including long-term undertaker procedures at the time of death.

Some things to note:

Since there are only a relatively small number of these prostate cancer cases, not all radiation therapy centres offer the iodine-125 seed option.
The I-125 seed implant technique requires a high level of skill by a team of medical specialists – the radiation oncologist, urologist and medical physicist who prescribe, implant the I-125 seeds and calculate the treatment method, respectively. All three specialists must receive skilled training at another recognised I-125 seed brachytherapy centre before offering a local service.
There must also be a sufficient number of I-125 prostate implant cases to maintain the requisite specialist skills and have sufficient records to analyse treatment outcome and quality of care. Urologists wishing to establish a robotic surgery technique follow a similar treatment standard of practice.
The Urology surgeon manually implants the iodine-125 seeds into the prostate according to a calculated plan. The number and distribution of I-125 seeds implanted into the prostate varies depending on the prostate and tumour size and shape. The urethra passes through the centre of the prostate. To avoid unnecessary irradiation causing urethritis after surgery, the I-125 seeds must not be implanted too close to the urethra.

Figure 3. a graphic diagram of the anatomy showing the needles passing through the grid guide and into the prostate.

Figure 3. shows a graphic diagram of the patient’s anatomy with the needles passing through the grid guide and into the prostate.The ultrasound probe is inserted into the rectum (located posteriorly to the prostate).

Figure 4. X-ray image of the implanted I-125 seeds and the surrounding anatomy.

Figure 4. is an enlarged X-ray image of the same anatomical arrangement as Figure 3.

Figure 5. The ultrasound probe inserted into the patient’s rectum provides a dynamic image of the needles being inserted into the prostate and the surrounding anatomy.

The ultrasound probe is inserted into the patient’s rectum to provide a dynamic image of the needles being implanted into the prostate (Figure 5.). This helps the surgeon to see that the seeds are accurately inserted according to the treatment plan. The surrounding anatomy is also visible in the image.

Figure 6. Pelvic X-ray image showing all the I-125 seeds implanted into the prostate.

Figure 6. shows a 2-dimensional Xray image taken of the patient’s pelvic area. There can be as many as 100 or so I-125 seeds implanted. The seeds tend to migrate or twist slightly after the needle is removed leaving the seeds behind in the prostate tissue (Figure 6.).

Figure 7. CT Scan of the patient after the I-125 seed operation.

After the I-125 seed implant operation is finished, the patient must have a CT scan. This is so that the medical physicist can calculate by computer what the true dose distribution is. The ‘final’ implant is normally not an exact replica of the initial ‘ideal’ seed distribution. Some of the needles may be slightly different to what was intended and, as shown in Figure 6., some of the seeds can move or skew slightly.
The most recent I-125 seed brachytherapy equipment calculates the dose distribution as the surgeon inserts the seeds in the needles (see the video below). This enables the surgeon to take corrective action if the dose is not as originally planned.

Patients recover quickly after surgery and are normally discharged to go home within 48 hours after the operation.

High Dose Rate (HDR) Brachytherapy

Radioactive iridium-192

The technique for inserting the needles with the help of ultrasound imaging is virtually the same as for an Iodine-125 implant method. But instead of implanting the I-125 seeds permanently, a radioactive iridium-192 source (Ir-192) is remotely inserted into each needle sequentially to temporarily irradiate the prostate cancer tissue.
Ir-192 is a much higher activity radioactive source than the I-125 seeds. The Ir-192 is attached on the end of a cable and driven remotely out of a shielded high-dose-rate (HDR) treatment unit, passed through connecting tubes and the needle inserted in the prostate. The Ir-192 irradiates the prostate for a calculated time (within minutes).
At the end of the treatment time, the Ir-192 source is automatically withdrawn back out of first needle to the HDR unit and changes to the next catheter- needle until the planned treatment is completed.
At the completion of the operation, the patient return to the ward for recovery and can be discharged within 48 hours.
There’s no residual radioactivity left in the patient after the treatment.

Radiation Therapy and Brachytherapy Complications

Modern external beam radiation therapy and brachytherapy techniques have significantly reduced the incidence of bladder and rectal complications.

As is the case for external beam radiation therapy, brachytherapy techniques do not cause erectile dysfunction immediately but sexual deterioration will eventually occur earlier than normal.

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Ablation Devices

Most patients choose surgery or radiation therapy but some may consider ablation type techniques. There are prostate cancer treatment procedures of cryosurgery, high-intensity focal ultrasound, photodynamic therapy, radiofrequency ablation and laser-induced interstitial thermotherapy. The most recent ablation technique developed is called electroporation. There will be an update in the next article reporting on a current World trial using an electroporation NanoKnife device to treat prostate cancer patients.