Urological Associates | Brachytherapy

RADIATION SEED IMPLANTS FOR THE TREATMENT OF PROSTATE CANCER

It has been estimated that the lifetime risk for a man in Western society of developing microscopic prostate cancer is around 30%, 10% of which will develop into potentially dangerous cancer.

The challenge, therefore, is to accurately distinguish these dangerous cancers from those considered insignificant. Although strides have been made in prognosis through evaluation of tumor stage, grade and volume, DNA analysis and molecular markers, the call to accurately predict important cancers has not been completely answered. In this setting, the decision to choose and undergo treatment is, at times, confusing and difficult for the uninformed patient. Today, a minimally invasive effective treatment alternative, called prostatic interstitial radiation seed implantation, or brachytherapy, exists and is appropriate for many early stage, low to moderate grade prostate cancers.

Improvements in the way radiation is delivered to the prostate is considerably changing the treatment of clinically localized (organ confined) prostate cancer, expanding patient's options and, perhaps, narrowing the indications for radical surgical removal of the prostate. This form of radiation therapy provides an alternative to watchful waiting and radical surgical removal of the prostate for organ-confined disease and may render a definitive "cure". While enormous strides continue to be made in external beam radiotherapy, no modality has benefited more from technological advances than radiation seed implantation. Transrectal ultrasound, or TRUS, and computed tomography, or CT imaging techniques, improved forms of seeds, and computerized dose calculations for accurate radiation dosing have revived and reined an old technique.

Previously, radiation seeds were implanted through an open abdominal incision into the prostate when organ confined cancer was suspected. This technique was abandoned due to high local recurrence and metastatic recurrence rates. These failures were due in large part to under dosing whole areas of cancer due to poor geographic placement and distribution of seeds. With modern brachytherapy, seeds are delivered through a needle placed into the perineum, with no incision, using either CT pre-planning and/or ultrasound guidance. This significantly reduces distribution errors.

It appears, from information gathered over an eight to nine year period, that seed implantation reduces death rates from prostate cancer and improves local disease control better than external beam radiotherapy and nearly as well as surgical removal of the prostate for certain types of cancer.

Interstitial seed implantation is carried out as a same day or overnight procedure, usually under a general anesthetic. An ultrasound probe is placed in the rectum and is used to guide needle placement of radiation seeds into the prostate. The needles are placed through a template grid completing a three-dimensionally preplanned distribution of seeds and dose.

Using transverse ultrasound images the needles are advanced into the gland until seed distribution is optimized in each plane' - through the gland. Seeds are then deposited under ultrasound as needles are withdrawn. CT scans are performed post-operatively to evaluate for any areas of under dosing. Usually, the bladder catheter is taken out the same day or left in overnight. This is, therefore, a truly minimally invasive approach.

It is important, in deciding upon treatment with seed implantation, to select only a patient for whom this technique would be appropriate. Candidates for the interstitial implantation of seeds have clinically localized disease, adequate life expectancy to make a cure worthwhile, no colorectal disease, no recent TURP (transurethral resection of the prostate), and absence of lower urinary disease. Complication rates have been reduced from between 5 and 20% in the surgical implantation approach, to less than 5% with the incisionless needle placement, and are superior to complication rates .of external beam therapy. Some patients, however, do experience acute problems of urination, including urgency and frequency during the seeds' active life. This typically lasts a few days to a couple of weeks. Only 10% of these cases require treatment with medication or temporary bladder catheterization Potential late complications include urinary incontinence in less than 1% of patients (although there is a 12% incontinence if seeds are placed after TURP), a 4% incidence of urethral stricture and a 2% chance of proctitis (rectal irritation and diarrhea).

The primary dilemma in prostate cancer management continues to be uncertainty in differentiating those cancers confined to the prostate, and those which have spread (and are therefore not amenable to this form of treatment). At present, seed implantation has no proven effect on disease outside the prostate. In prostate confined disease, the results of modern seed implantation has been encouraging, especially when compared to outcomes of the old, retropubic implantation technique. In general, encouraging results have been seen at 5 years, with success rates for stages T1 and T2 of around 96% and 89% respectively. Post-treatment biopsy results at five years were equally encouraging with 87% disease free after modern seed placement. Seeds are not, however, appropriate for all cancers, whether organ confined or not. This further emphasizes the need for careful patient selection.

Still, despite short term success, long term data and randomized head to head trials against the traditional organ-confined treatments, surgical removal of the prostate and external beam radiotherapy, are not yet available. In comparable external beam series, seeds seem to have better disease free survival statistics than external beam recipients. Caution must be used in endorsing seed implantation in all cancer scenarios, since history has shown a late propensity for recurrence of cancer after all forms of radiotherapy. Presently, despite its potential complications, the surgical treatment option offers more assured "cure" potential for accurately staged (T1 or T2) disease.

From a urologist's perspective the decision whether and how to best treat prostate cancer is dependent on three factors: disease extent or stage, patient age, and general health (factoring in other ongoing illness). No one fact simplifies this complicated decision making process. To reiterate, one third of men have small foci of prostate cancer but only 10% will develop into clinically significant disease. However, 80 to 90% of cancers detected by elevated PSA (prostate specific antigen) are clinically important and warrant treatment in men with a 10 year or greater life expectancy. So, when is it necessary to treat prostate cancer? For now, this is best answered by a urologist informing patients about research results based on stage and grade of the cancer. The patient must weigh the negative side effects of treatment options against the likelihood of success. Given this degree of uncertainty, there is clearly a place for a minimally invasive treatment option with minimal side effects for cancers which are of questionable significance.

Radiation seed implant not only fulfills this need, it may eventually replace surgical removal of the prostate as the curative "gold standard" for clinically confined, low moderate grade prostate cancer. This is the current trend. Only time will answer whether the short term successes of seed implantation are followed by long term cures.

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