Promising Prostate Cancer Treatment Should Be Considered Experimental
(PHILADELPHIA)— Despite the growing desire by radiation oncologist to use high-dose brachytherapy alone to treat prostate cancer, the treatment should be considered experimental at this point, say researchers at Thomas Jefferson University's Kimmel Cancer Center.
In the Volume 14, Issue 1 of the journal Expert Review of Anticancer Therapy, the scientists say that as promising as high-dose brachytherapy appears to be, there is not enough evidence yet to support its use as mono-therapy — a stand-alone treatment — for prostate cancer.
"We don't fully know how effective high-dose brachytherapy alone is, and we don't fully know the toxicity that is associated with its use," says the study's lead investigator, radiation oncologist Nicholas G. Zaorsky, MD.
High-dose brachytherapy is now only used as a "boost" to external beam radiation in treatment of prostate cancer — that is, high-dose rate brachytherapy is not used alone.
Low-dose brachytherapy is also a common treatment option for low- and intermediate-risk prostate cancer patients, but high-dose brachytherapy differs in significant ways, Dr. Zaorsky says.
During a high-dose brachytherapy procedure, a computer-guided system automatically deploys and retracts a single small radioactive source along the implant needle at specific positions in the prostate. This radioactive source stops for a certain amount of time at each position in the prostate. According to Dr. Zaorsky, the accurate, high dose of radiation delivered from the radioactive source, is, in theory, very effective at killing prostate cancer cells, and has very little spill-over to nearby healthy tissues, which is associated with side-effects.
In high-dose rate brachytherapy "boost," external beam radiation therapy is used to deliver additional radiation. The external beam radiation is delivered to the prostate and surrounding tissues and lymph nodes, which may potentially harbor disease that has spread outside of the prostate. "However, if we are fairly certain that cancer is confined to the prostate, then the use of boost therapy may not be necessary — high-dose rate brachytherapy alone may be enough," says Dr. Zaorsky.
In comparison, in low-dose rate brachytherapy, radioactive seeds are permanently implanted into the prostate. While the use of low-dose rate brachytherapy seeds has been shown to be an effective treatment option for many prostate cancer patients, seeds do not deliver a high dose of radiation in a short period of time, and the dose may spill-over to healthy organs, which is associated with generally minor or moderate side effects that resolve over time, Dr. Zaorsky says.
"High-dose rate brachytherapy alone appears to be a very promising treatment for certain prostate cancer patients," says Adam Dicker, MD, PhD, Professor and Chairman of radiation oncology, Thomas Jefferson University Hospital.
"Still, only two prospective studies using high-dose brachytherapy alone have been published, and to date, we have little information about long term outcomes or long-term toxicity," he says. "There could be recurrence of the cancer or cancer spread over time, or complications such as progressive scarring of the urethra that occur years after therapy.
"There are many treatment options available for prostate cancer right now. High-dose brachytherapy alone is promising and in the coming years there will be more phase II and phase III studies that will clearly define for whom this treatment option could be used," says Dr. Zaorsky. "We just have to follow it longer."
Jefferson currently offers high dose-rate boost brachytherapy as part of its comprehensive prostate cancer service.
Researchers who participated in this study were Laura A. Doyle, MS; Mark D. Hurwitz, MD; Adam P. Dicker, MD; and Robert B. Den, MD.
This work supported in part by the Kimmel Cancer Center's NCI Cancer Center Support Grant P30 CA56036, as well as by Young Investigator Awards from the Prostate Cancer Foundation to Dr. Robert B. Den, the senior author of the study.
Dr. Zaorsky conducted this research while at the Kimmel Cancer Center. He is currently at the Fox Chase Cancer Center in Philadelphia.
The authors declare no conflicts of interest.