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Understanding Brachytherapy

History of HDR Brachytherapy

To understand the High Dose Rate (HDR) brachytherapy  system, one needs to know about the Low Dose Rate (LDR) brachytherapy system in order to compare the two.

LDR, once the only type of brachytherapy available, has limitations:

  • Limited ability to shape or conform the radiation to fit the tumor. In the case of permanent seeds, once they are inserted into the tissue, nothing can be done to change their position, or the amount of radiation they will emit.
  • LDR treatment times are long.  LDR gynecologic cases require a two day hospital stay where the woman must remain in bed as motionless as possible, in order to minimize movement of the applicator inside her which contains the radioactive sources.  Permanent seeds, used to treat prostate cancer, require weeks and months to deliver the prescribed dose, during which time they can shift around inside the prostate or migrate entirely out of the prostate to end up in the bladder, urethra, rectum, pelvic cavity and lungs. Any movement of the LDR applicator or seeds results in uncertain doses to the tumor and nearby structures. 
  • Because the patient is radioactive, radiation protection precautions have to be observed so that exposure to others is kept to a minimum.

It was because of these limitations the high dose rate technology was developed.

The HDR system uses a single, tiny, (1mm x 3 mm) highly radioactive source of Iridium-192 that is laser welded to the end of a thin, flexible stainless steel cable. The source is housed in a device called an afterloader. The computer-guided afterloader directs the source into the treatment catheters or applicator that has been placed in the patient by the brachytherapy physicians. The source travels through each catheter in 5mm steps, called "dwell" positions. The distribution of radiation and dose is determined by the dwell positions the source stops at and the length of time it dwells there. This ability to vary the dwell times is like having an unlimited choice of source strengths. This level of dose control is possible only with HDR.

A major advantage of HDR is that we know what the final doses will be before any radiation treatment is given. Because the patient and implant position is the same as when the treatment plan was devised, the doses are accurate.

Nucletron Corp. microSelctron HDR afterloader.

Fig 1: Nucletron Corporation's microSelectron HDR afterloader Due to high radioactivity of the Iridium-192 source, the treatment time is in minutes so there is little opportunity for the implant to move and deposit radiation dose where it's wasn't intended. HDR dose accuracy is measured in millimeters.

Because the afterloader controls the radiation source, radiation exposure to the physicians, hospital staff and family members is eliminated. After the HDR treatment the source retracts into the afterloader. The patient is no longer radioactive. That is why HDR brachytherapy implants are called temporary implants.
HDR brachytherapy treatment courses can be form 3 to 10 treatments, depending on the type of cancer being treated. There are many factors that the physician considers in determining the radiation dose and how many treatments an implant should receive.

 

Typical HDR Procedures

Step 1: Implant placement

The UCLA physicians decide which type of implant the patient requires, based on location, tumor extent and other factors. The three types are:

  1. Intracavitary Implant: an applicator is inserted into a body cavity to reach the tumor. Intracavitary implants are performed in the Brachytherapy Suite in the UCLA clinic on an out-patient basis. Local anesthesia and/or conscious sedation is all that is required.
  2. Intraluminal Implant: the catheters are inserted into a "tube" structure such as the bronchus, esophagus, or bile duct. These are treated the same as intracavitary implants on an outpatient basis.
  3. Interstitial implant: are more complex. The implants are done in the operating room with the patient under local, general or spinal anesthesia. Interstitial catheters are inserted through the body tissue to encompass the tumor. In the case of prostate and gynecologic cases, a rubber template is sutured to the outside skin to hold the treatment catheters in position. In breast and head and neck cases, the treatment catheters are held in position on the skin by plastic buttons where the catheters enter and exit the skin.

Step 2: Simulation

after the implant has been placed, either CT or special x-ray films are taken by the radiation therapists to determine the exact location of the implant in the body and the relationship to adjacent organs. The therapists' expertise in taking these films assures that the implant and nearby organs are visualized clearly. The physician reviews these films and makes final adjustments to the implant if necessary.

Step 3: Dosimetry

The CT images or films are given to the dosimetrist to enter into the treatment planning computer. The computer does the initial calculation but it is the dosimetrist who "fine tunes" or customizes the radiation doses to conform to the target volume while minimizing the doses to the nearby normal tissues. After the treatment plan has been approved by the physician, the computer transfers the treatment plan instructions to the HDR remote afterloader.

Step 4: Treatment

The patient is moved into the brachytherapy treatment room. The ends of the applicator or treatment catheters that protrude outside the body are connected to "transfer" tubes which are then connected to the afterloader. The programmed instructions tell the afterloader where to direct the source and how long the source will stay in each dwell position. The patient is alone in the treatment room while the treatment is being given, but the therapists and nurses are continually monitoring the patient through an intercom and closed circuit TV monitors. The entire treatment process takes about 30-90 minutes depending on the size and complexity of the implant and the activity of the source. When the treatment is completed, the radiation source is retracted back into the HDR afterloader. There in no radiation left behind in the patient.

Step 5: Implant Removal

After the treatment(s) have been given, the implant is removed. Intracavitary and intraluminal applicators are simple to remove and the patient goes home soon after removal. With interstitial implants, sutures holding the template and/or catheters in place are clipped and the implant is gently removed. Some minor bleeding usually occurs, which is quickly stopped by applying direct pressure to the implant site with gauze pads. Post- implant skin care instructions are given by the nurses before the patient leaves the UCLA clinic or hospital. A date for a follow-up appointment will also be given.

Step 6: Follow-up

It is important that the patient keep us informed as to their recovery, any side effects, PSA results, etc. We pride ourselves on thorough patient follow-up, which is how we assess the efficacy of our HDR treatments and provides us with the data necessary in order to report our results in the medical literature.

Click here to visit our Brachytherapy FAQs section.

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