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High Dose Rate (HDR) Brachytherapy
IMRT, without question, is a safer way of delivering external beams than older beam methods - but for prostate cancer, brachytherapy gives an even higher and more precise radiation dose, and brachytherapy does it from the ‘inside out’ where external radiation has to penetrate from the outside as it goes in.
There are two versions of brachytherapy available:
- permanent seed implants
- temporary implants
Some cancers will do fine with the slower delivery and more restricted doses of Low Dose Rate (LDR) or permanent seed brachytherapy. Others will benefit from the rapid radiation delivery and greater safety margin of High Dose Rate (HDR) temporary brachytherapy.
Gamma West Cancer Services is the only clinic in the Intermountain West (and one of just a few in the nation) to offer both LDR permanent seed brachytherapy, and HDR temporary brachytherapy. We perform over 500 of these implants per year making us one of the biggest brachytherapy clinics in the country. HDR seems to be less familiar to many Urologists (and patients) than permanent seeds, yet is a treatment used much more often than permanent seeds in those clinics where both are available.
About LDR Permanent Seed Brachytherapy
LDR permanent seed brachytherapy is appropriate for those patients with early, favorable disease only. We use the following criteria to define favorable disease: Gleason score (the grade of tumor aggressiveness) of 6 or less, PSA of 10 or less and not rapidly doubling, a small or preferably no tumor nodule, and minimal involvement in the biopsy needles. The Partin Tables show that patients with these favorable features have disease that is likely organ confined. Permanent seeds are a great treatment for disease confined to the prostate, but seeds are inadequate for a cancer with higher risk features that may be out of the prostate, even if it’s extending out of the prostate just a few millimeters.
Reasons why permanent seeds will not be very effective when treating higher risk tumors.
- The radiation emitting from LDR seeds is extremely confined, and will not reach much beyond the prostate to cover cancer extending through the prostate’s capsule or up into the seminal vesicles, both of which are very real possibilities in the medium and higher risk patient.
- Permanent seeds do not have the ability to deliver the radiation quickly. If a tumor is felt to be faster growing (high Gleason score or rapidly rising PSA), the low dose rate permanent seeds will not kill it very well because the seeds release the radiation much too slowly. In other words, the tumors growth rate exceeds the rate that it’s being killed because the seeds can’t release the radiation quickly enough. Moreover, seeds are permanent in the prostate where they remain radioactive for nearly one year. Patients who struggle with their urination (AUA urine symptom score around 20 or greater) will have longer lasting and more severe urinary problems after seeds than they will after the temporary or HDR implants, which will usually cause urinary problems for only a few weeks. On top of all that, patients getting permanent seeds have to follow radiation precautions for two months, and in an environment as family oriented as the Intermountain West, many men find it difficult to not hold grandchildren during this time.
Despite saying all this, we absolutely do believe in permanent seed brachytherapy as a highly effective treatment for early prostate cancer. I have pointed out some of seeds shortcomings, but seeds have some advantages as well, such as no need for external beam radiation, and that it is an outpatient procedure. Nevertheless, there is a large group of prostate cancer patients for whom HDR brachytherapy is more appropriate.
The HDR radioactive source is thousands of times more active than a permanent seed. HDR implants treat a wider area around the prostate than seeds, including the seminal vesicles and much of the peri-prostatic fat, so the “safety margin” of the treatment is greater. HDR brachytherapy delivers a very high radiation dose in a very short period of time which is especially important for those tumors that we feel may be faster growing (i.e. higher Gleason scores, or rapidly increasing PSA’s). Urinary side effects are relatively short and no radiation precautions need to be followed because HDR is a temporary implant.
With HDR implants, we place the needles in the prostate and seminal vesicles, and then plan the treatment based on actual needle location. Permanent seed planning is done on a computer model a few weeks before the implant, and then we attempt to reproduce that plan in the operating room. However, with permanent seeds, the needles often don’t end up in the exact pre-planned location, and the permanent seeds sometimes migrate along the needle tracts away from their ideal position. With HDR brachytherapy, the radiation source (which is about the same size as a permanent seed, only much more radioactive) is securely attached onto the end of a thin, flexible wire cable. Powerful computers precisely control the movement of this cable with a tolerance of less than 1mm. This cable is then inserted into a series of hollow implant needles that are placed into and around the prostate gland. The HDR treatment is delivered as the radioactive source moves to different positions within each needle.
The placement of the implant needles is done in the operating room under a spinal anesthetic. It takes less than one hour to place the needles. Three times in the next 24 hours a short 15 minute treatment is given through the needles in the Gamma West clinic: the first is in the afternoon on the day the needles are placed, the second is first thing the following morning, and the third and final treatment will be 6 hours later, just after lunch. The needles are then removed, the catheter in the bladder is taken out, and the patient is sent home.
HDR technology allows nearly endless possibilities for dose customization by adjusting the position within the needles the source travels to, and by adjusting the time spent at each of the source treatment positions. We plan the HDR treatments with CT images obtained just after the needles are placed. The implant needles and relevant anatomy (bladder, urethra, rectum, seminal vesicles, and prostate) are reconstructed from the CT images in 3-D on our treatment planning computers. We know with great accuracy what dose is actually being delivered to the rectum, bladder, and urethra, as we ensure that lethal doses are given to the prostate, seminal vesicles, and peri-prostatic areas. The HDR brachytherapy approach has become the preferred treatment for patients with higher PSA’s, higher Gleason scores, and stage T2, T3 and even T4 disease (the most advanced stage) because of its ability to treat beyond the prostate as outlined above. The superior outcomes with HDR, the low risk of complications, the advantage of not being radioactive after the implant, and the real-time interactive planning define a new standard for treatment of high-risk prostate cancer.
Robert Stephenson M.D., Professor and Jon M. Huntsman Chair of Urological Oncology at the Huntsman Cancer Institute compared quality of life in our seed patients (who had favorable disease) to our HDR patients (who had high-risk disease). QOL scores were superior with HDR, despite the fact that their disease was worse and their treatment more aggressive, primarily because the urinary side effects were less and of shorter duration. Another unexpected finding was the exceptional biochemical cure rates in the HDR group which nearly equaled that of the permanent seed group who had much more favorable disease. Partly because of this data, the use of HDR has now become a very attractive treatment option for those with early favorable disease as well.
HDR implants are done one of two ways:
- As a boost of radiation after being treated first with 5-weeks of external beams.
- As the sole form of radiation – which we call HDR Monotherapy. In other words, all the radiation is given with HDR brachytherapy.
Which of the HDR options to treat with depends on how far beyond the prostate the cancer may have spread. The version where 5-weeks of external radiation are given first is the broadest and most comprehensive treatment available for prostate cancer. The 5-weeks of external beam radiation treatments are directed to the majority of the pelvis in order to also encompass the pelvic lymph nodes. This dose of 4500 cGy is well tolerated, and is nearly always sufficient by itself to eradicate microscopic cancer that may have escaped beyond the prostate into these areas. However, the prostate, seminal vesicles, and peri-prostatic fat, which harbor the bulk of the disease, need to be treated to much higher radiation doses to achieve the greatest possibility of cure. 4500 cGy will kill microscopic disease only, and is not sufficient for bulky or measurable disease. This further dose escalation is done with HDR Brachytherapy. The implant delivers this very high dose (higher than can be given with any version of external beams) with little additional radiation going to the bladder or rectum.
For low-risk and some medium-risk patients, the likelihood of cancer in the lymph nodes is negligible, and they can be treated with HDR brachytherapy alone. We call this “HDR Monotherapy.” This treatment protocol delivers a full complete radiation dose over two separate implants, each approximately 1-4 weeks apart. HDR Monotherapy has all of the advantages of HDR listed above, and avoids the external radiation. Not every patient will be eligible for this treatment, however. We won’t offer HDR Monotherapy to the very high-risk patients feeling that they will have a very important benefit to the 5-weeks of external radiation. As mentioned above, 5-weeks of external radiation gives a dose sufficient, in most cases, to eradicate microscopic disease that may be at a significant distance from the prostate, such as out in the lymph nodes. HDR Monotherapy will not give any meaningful dose as far out as the lymph nodes, but will adequately treat the prostate, seminal vesicles, and peri-prostatic tissues.
When HDR implants alone are used, two implants are required approximately 1 to 4 weeks apart from each other. One implant gives the radiation dose that the external beams would have given, and the other implant gives the rest of the needed radiation dose.
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